Acids Bases and Salts - Text

Acids Bases and Salts

Class X Chapter 2

You have learnt in your previous classes that the sour and bitter tastes of food are due to acids and bases, respectively, present in them. If someone in the family is suffering from a problem of acidity after overeating, which of the following would you suggest as a remedy– lemon juice, vinegar or baking soda solution? Why everything tastes so differently? Why lemon is tangy and mango is sweet? This is because of different percentage of acids, bases, and salts in their chemical composition.

We all have heard the terms acids, bases and salts and often used them in your daily life; complained about the acidic nature of food components, used soap and ammonia for cleaning or heard about salt being created from seawater. Gaining a thorough understanding of Acids, Bases, and Salts class 10 is essential for understanding basic chemistry and extremely important.

Acids, Bases, and Salts are the main chemical compounds that exist in our surroundings. Acids, Bases, and Salts are compounds that occur naturally and can also be created artificially. They are found in various substances including our food. Vinegar or acetic acid is used as a food preservative. Citrus fruits have citric acid and etc.

Other than food they also have a wide variety of uses such as in various industries, manufacturing plants, processing plants, laboratories, and others. In this article, we will learn about Acids, Bases, and Salts, their properties, types, uses, and others in detail. The image given below shows acid and base which when reacting form salt.

In this video we learn about the definition, characteristics and properties of acids, bases and salts. Let’s learn how these can be characterized, understanding the concepts by Arrhenius, Bronsted-Lowry and Lewis etc.

Earlier, acids, bases, and salts were characterized by the experimental testing of their aqueous solutions. An acid is defined as a substance whose water solution tastes sour, turns blue litmus red and neutralizes bases. A substance is called base if its aqueous solution tastes bitter, turns red litmus blue or neutralizes acids. Salt is a neutral substance whose aqueous solution does not affect litmus. According to Faraday: acids, bases, and salts are termed as electrolytes. Further, Liebig proposed that acids are compounds which contain hydrogen that can be replaced by metals.

Acids: Acids are those that when dissolved in water, give hydrogen ion or we can write hydronium ion (H3O+) This hydronium ion is formed due to the combination of hydrogen ion produced by acid with water molecule. Acidity is a characteristic property of acids. Acidic substances are usually very sour. In fact, the word ‘acid’ and ‘acidity’ are derived from the Latin word ‘acidus’ which means sour. If you dip a blue litmus paper into an acid, it will turn red while a red litmus paper will not change colour. Acids also liberate dihydrogen when they react with some metals.

What are Acids?

Acids are a type of chemical substance that is characterized by their ability to donate hydrogen ions (H+) when dissolved in water. Acids can be found naturally in many foods and beverages, including citrus fruits, vinegar, and fermented products, and they are also used in various industrial processes. Here are some key points about acids:

Acids can be classified into two categories: organic acids, which are derived from living organisms, and inorganic acids, which are derived from non-living sources. Acids have a sour taste and can cause a tingling or burning sensation on the tongue or skin. The strength of an acid is determined by its pH value, which ranges from 0 to 14. Acids with a pH less than 7 are considered to be acidic, while those with a pH greater than 7 are basic or alkaline.

Acids can react with bases to form salts and water in a process called neutralization. Acids are used in a variety of industrial applications, such as the production of fertilizers, dyes, and pharmaceuticals. Some acids can be harmful or corrosive to living tissue, such as hydrochloric acid, which is found in the stomach and is necessary for digestion, but can cause severe burns if it comes into contact with the skin.

Acids are also used in various chemical reactions, such as in the production of polymers and plastics, as well as in the cleaning and sterilization of medical equipment.

Example of acids are:

hydrochloric acid (HCl)

sulphuric acid (H2SO4)

nitric acid (HNO3)

phosphoric acid (H3PO4)

carbonic acid (H2CO3)

Classification of Acids: we have different classification based on different factors so let’s sum up and make ourselves familiar with it. Depending upon source from which they are obtained: Organic acids & Inorganic acids

Organic Acids are obtained from plants and animals or we can say they are present in organic matter.

Inorganic Acids are those that are obtained from minerals present in earth. These are quite reactive in nature. Example we have are: nitric acid, sulphuric acid, etc.

Physical Properties of Acids

Acids are chemical substances that have unique physical and chemical properties. Here are some of the physical properties of acids:Acids have a sour taste: Most acids have a distinctly sour taste, such as lemon juice and vinegar.

Acids change the color of indicators: Acids change the color of certain indicators, such as litmus paper, which turns red in the presence of an acid.

Acids are corrosive: Many acids are corrosive and can cause damage to living tissue or corrode metal and other materials.

Acids have a low pH: The pH scale measures the acidity or alkalinity of a solution, with a pH of 7 being neutral, and lower pH values indicating greater acidity. Acids typically have a pH of less than 7.

Acids react with bases to form salts and water: When an acid reacts with a base, the two substances neutralize each other, forming a salt and water.

Acids have a higher boiling point than water: Acids generally have a higher boiling point than water, which means that they require more energy to boil than water.

Acids are good conductors of electricity: In a solution, acids can conduct electricity because they contain charged particles known as ions.

Acid is a compound which yields hydrogen ion (H+), when dissolved in water. HCl + H2O → H+ + Cl- Acid is sour to the taste and it is corrosive in nature. The pH of acids is less than 7. All acids react with metal to release hydrogen gas. For example, zinc metal reacts with hydrochloric acid to form zinc chloride and hydrogen gas.

Zn + 2HCl → ZnCl₂ + H₂

When acids react with limestone (CaCO₃), it produces carbon dioxide. For example,HCl reacts with limestone to produce carbonic acid and calcium chloride. CaCO₃ + 2HCl → CaCl₂ + CO₂ + H₂O

Acids are classified into organic and inorganic acids. The best example of organic acid is acetic acid CH₃COOH, and inorganic acids are those which are produced from minerals; for example, sulphuric acid H₂SO₄, and hydrochloric acid, etc. Acid usually converts blue litmus paper to red litmus paper. Acids have a tendency to quickly corrode the metal surfaces.

On the Basis of Number of Hydrogen Ion, Acids can be classified as:

Monoprotic Acid – They can produce one mole of H+H^{+} ions per mole of acid, ex - HCL.

Diprotic Acid – They can produce two moles of H+H^{+} ions per mole of acid, ex - H2SO4H_{2}SO_{4}

Triprotic Acid – They produce three moles of H+H^{+} ions per mole of acid, ex - H3PO4H_{3}PO_{4} On the Basis of Strengths to Donate Hydrogen Ions,

Acids can be Classified as:

Strong Acids: These acids get completely (100%) ionized in the aqueous solutions. Thus, at equilibrium, the concentration of acid molecules becomes very less and concentration of hydrogen ion reaches to the maximum; for example, HCl,HNO3,HClO4

Weak Acids: These acids are only partially ionized in solution at equilibrium state. At equilibrium state, molecules of acid are present in a considerable amount and the concentration of hydrogen ion is less, for example, HF,CH3COOH

Chemical Properties of Acid

Acid has various chemical properties few of the following chemical properties of acids include,

Reaction of acids with metal: When an acid reacts with a metal, it produces hydrogen gas and the corresponding salt. Metal + Acid → Salt + Hydrogen. Example: When hydrochloride acid combines with zinc metal, it produces hydrogen gas and zinc chloride. Zn + 2HCl → ZnCl2 + H2

Reaction of acids with metal carbonate: When acids react with metal carbonates, they produce carbon dioxide gas and salts as well as water.

Metal carbonate + Acid → Salt + Carbon dioxide + Water. Example: When hydrochloric acid combines with sodium carbonate, it produces carbon dioxide gas, sodium chloride, and water. Na2CO3 + 2HCl → 2NaCl + H2O + CO2

Reaction of acid with hydrogen carbonates (bicarbonates): When acids react with metal hydrogen carbonates, they produce carbon dioxide gas, salt, and water. Acid + Metal hydrogen carbonate → Salt + Carbon dioxide + Water Example: Sulfuric acid gives sodium sulfate, Carbon dioxide gas and water when it reacts with sodium bicarbonate.2NaHCO3 + H2SO4 → NaCl + CO2 + H2O

Types of Acids

Acids are classified into different categories, the classification of acids is discussed below in the article. On the basis of their Occurrence acid are subdivided into two categories; Natural Acid & Mineral Acids

Natural Acid: Natural acids, often known as organic acids, are acids derived from natural sources. For example Methanoic acid (HCOOH), Acetic acid (CH3COOH), Oxalic acid (C2H2O4), etc.

Mineral Acids: Mineral acids are acids that are created from minerals. Inorganic acids, man-made acids, and synthetic acids are all examples of Mineral Acids. For example Hydrochloric acid (HCl), Sulphuric acid (H2SO4), Nitric acid (HNO3), Carbonic acid (H2CO3), Phosphoric acid (H3PO4), etc.

Uses of Acids: Acids have various uses some of the important uses of acid are,

Hydrochloric Acid: Hydrochloric acid is used in different industries for heating applications. This acid is applied to remove deposits from the inside of the boiler. It is also used to clean silverware and sinks.

Sulphuric Acid: Sulphuric acid is used to manufacture paints, dyes, drugs, and fertilizers. In batteries, sulfuric acid is commonly utilized. This acid is typically found in the batteries used to start vehicle motors. Sulfuric and nitric acid is used in the industrial production of dyes, explosives, paints, and fertilizers.

Nitric Acid Goldsmiths use nitric acids to clean gold and silver ornaments. Nitric acid is also used for manufacturing fertilizers. Orange and lemon juice contain a significant amount of citric acid. It can also be used for food preservation.

Acetic Acid: Acetic acid can be used as a cleaning agent to clean windows, utensils, floors, etc. Acetic acid is an effective ingredient to enhance the flavor of food items. Acetic acid helps in the removal of stains from woodwork and carpets. Vinegar is a diluted solution of acetic acid that has a variety of uses in the home. It’s mostly utilized in the food industry as a preservative. Acetic acid is used as a preservative in packaged foods such as sauces, ketchup, pickles, etc. Many soft drinks contain phosphoric acid as the main ingredient.

Bases

If we talk about bases, according to Arrhenius, they are those that when dissolved in water give hydroxide ion (OH-). Example: Calcium hydroxide Ca(OH)2 Magnesium hydroxide Mg(OH)2.

Bases turn red litmus paper blue while the blue litmus paper stays blue. They taste bitter and also feel soapy. Some other common examples of bases include sodium bicarbonate that is used in cooking and household bleach.

What are Bases?

Bases are chemical compounds that react chemically with acids, they produce salts and hydroxide ions (OH–) in water. For example Potassium hydroxide (caustic potash or KOH), Calcium hydroxide (Ca(OH)2), Sodium hydroxide (caustic soda or NaOH) etc.

Properties of Bases: Bases are compounds that yield hydroxide ion (OH−), when it is dissolved in water. Bases are bitter in taste and are corrosive in nature. They usually feel slippery and very soapy. Bases are good conductors of electricity and usually show a pH value of more than 7. Bases react with oils and grease to form molecules of soap. Bases convert red litmus paper to blue litmus paper. Bases also have the tendency to corrode the surface of metals.

Strength of Bases-Strong Bases: That completely dissociates in water to give hydroxide ions. These bases totally dissociates and leave no dissociated molecule of base. These are the bases which are completely ionized in water to produce hydroxide ions, e.g., Hydroxides of all reactive metals.

Weak Bases: That do not completely dissociates in water to give hydroxide ions.These are the bases which are partially ionized and the equilibrium lies mostly towards the reactants side, e.g., Calcium hydroxide etc.

Physical Properties of Base

Bases have specific physical properties and they can easily be distinguished by their physical properties. Some physical properties of bases are: Base has a bitter taste. Bases are soapy to touch. Base change red litmus to blue. Aquous solution of base conducts electricity.

Chemical Properties of Base

Bases have various chemical properties few of the following chemical properties of bases are,

Reaction of Base with Metals: When alkali (base) reacts with metal, salt and hydrogen gas is produced. Alkali + Metal → Salt + Hydrogen

Example: When sodium hydroxide interacts with aluminium metal, sodium aluminate and hydrogen gas are generated. 2NaOH + 2Al + 2H2O → 2NaAlO2 + 2H2

Reaction of Non-Metallic Oxides with Base: Salt and water are formed when non-metallic oxides react with a base. Non-metallic oxide + Base → Salt + Water. Example: When calcium hydroxide reacts with carbon dioxide calcium carbonate is formed along with water. Ca(OH)2 + CO2 → CaCO3 + H2O

Action of Alkalis/Base with Ammonium Salts: Ammonia is produced when alkalis react with ammonium salts. Alkali + Ammonium salt →Salt +Water + Ammonia. Example: When calcium hydroxide reacts with ammonium chloride, calcium chloride, water, and ammonia are produced. Ca(OH)2 + NH4Cl → CaCl2 + H2O + NH3

Types of Bases

Acidity, concentration, and degree of ionization are three variables that can be used to classify bases. Based on Acidity: The number of hydroxyl ions presents determines acidity in bases. Based on acidity, bases are classified into three categories: Monoacidic, Diacidic & Triacidic

Monoacidic: Mono-acidic bases are those that contain only one hydroxyl ion and interact with only one hydrogen ion. Mono-acidic bases include NaOH, KOH, and others.

Diacidic: Diacidic base is a base with two hydroxyl ions that interact with two hydrogen ions. Ca(OH)2, Mg(OH)2, and other di-acidic bases are examples.

Triacidic: Triacidic base is a type of base that comprises three hydroxyl ions and three hydrogen ions. Triacidic bases include Al(OH)3, Fe(OH)2, and others.

Based on their Concentration

Based on their concentration in an aqueous solution, bases are divided into two categories: Concentrated & Diluted

Concentrated: The concentration of base in these types of bases is higher in the solution. Concentrated NaOH solution, for example.

Diluted: These types of bases have a lower concentration of base in their aqueous solution. For instance, dilute NaOH, dilute KOH, and so on.

Based on their Degree of Ionization

The degree of ionization of bases in solution can be used to classify them. It’s also known as foundation strength. When dissolved in water, it produces a certain quantity of hydroxyl ions. The degree of ionization distinguishes two types of bases. Strong Base &Weak Base

Strong Base: A strong base is one that dissociates entirely or to a large extent in water. For example, NaOH, KOH, and strong bases.

Weak Base: A weak base is one that does not dissolve entirely or only dissociates to a very little level. For example, NH4OH, and others are weak bases.

Uses of Bases

Base has various uses some of the important uses of the base are,

Calcium Hydroxide: Calcium hydroxide is used to neutralize acidity in the soil. Calcium hydroxide is a vital ingredient in mortar and whitewash It is an essential component of the Bordeaux mixture, which is used to protect agricultural crops from pests. Calcium hydroxide is also used to prepare dry mixes for painting. •Bleaching powder is made from Ca(OH)2, commonly known as calcium hydroxide or slaked lime.

Sodium Hydroxide: Sodium hydroxide is used in the production of detergents, textiles, and paper. Sodium hydroxide is used in households for unblocking drains. Sodium hydroxide is used in the making of paper and soap. Sodium hydroxide (NaOH) is also utilized in the production of rayon.

Ammonium Hydroxide: Ammonium hydroxide is used as a reagent in laboratories. Ammonium hydroxide is also used to manufacture plastic, dye, rayon, etc. In laboratories, ammonium hydroxide is a critical reagent. Slaked lime can be used to neutralize any excess acidity in soils.

Magnesium hydroxide, popularly known as milk of magnesia, is a laxative that is extensively used. It is also used as an antacid since it decreases excess acidity in the human stomach.

Alkali: Bases that are easily dissolved in water are called Alkali, in other words, water-soluble bases are called Alkali. For example, NaOH is an alkali as it dissolves in water forming Na+ and OH– ions.

Difference between Alkali and Base

The difference between Alkali and Base can easily be understood with the help of the table given below,

Addition of Acids or Bases to Water: The process of dissolving an acid or a base in water is highly exothermic. As this reaction usually generates a lot of heat, so there must be exclusive care taken while mixing the concentrated acids with water, especially when nitric acid or sulphuric acid is mixed with water.

Rules: The acid must be added slowly to the water with continuous and constant stirring, otherwise it can cause the mixture to splash out which in turn causes burns.

The glass container may also break due to excessive heating which can cause damage. When an acid or base is mixed with water, it results in dilution. It decreases the concentration of ions per unit volume thereby easily dissipating the effect of heat.

Ionization and Dissociation

Dissociation is the separation of ions from an ionic crystal when a solid ionic compound dissolves in water. On the other hand, ionization is the process where a neutral molecule breaks into charged ions when dissolved in a solution. The extent of ionization depends on the strength of the bonds between ions and the extent of solvation of ions.

The three most important modern concepts of acids and bases are:

Arrhenius Concept

According to Arrhenius concept, Substances which produce H+ ions when dissolved in water are called acids while those which ionize in water to produce OH– ions are called bases.HA → H+ + A– (Acid)

BOH → B+ + OH– (Base)

Arrhenius proposed that acid-base reactions are characterized by acids if they dissociate in aqueous solution to form hydrogen ions (H+) and bases if they form hydroxide (OH–) ions in aqueous solution.

Arrhenius’s Theory of Acid and Base

What is acid, what is base, and what is the difference between acid and base? these questions are nightmares to chemists in the early 15 and 16 centuries. To solve these questions a chemist name Arrhenius came up with a theory called Arrhenius theory. According to Arrhenius’s theory, a substance that gives H+ ion in its aqueous solution is called acid whereas the substance that ionizes OH– ion in the aqueous solution is called a Base.HCl(aquaous solution) ⇌ H+ + Cl–

NaOH(aquaous solution) ⇌ Na+ + OH–

Limitations of Arrhenius Concept

The presence of water is absolutely necessary for acids and bases. Dry HCl can’t act as an acid. HCl acts as an acid in water only and not any other solvent. The concept does not explain the acidic and basic character of substances in non-aqueous solvents. The neutralization process is only possible for reactions which can occur in aqueous solutions, although reactions involving salt formation can occur in the absence of a solvent. The acidic character of some salts such as AlCl3 in aqueous solution can’t be explained. An extended as well as artificial explanation is needed to define the basic nature of NH3.

Bronsted-Lowry Concept

Bronsted and Lowry in 1923 independently proposed a more general definition of acids and bases. According to them, an acid is defined as any hydrogen-containing material (molecule, anion or cation) which can donate a proton to other substance and a Base is any substance(molecule, cation or anion) that can accept a proton from any other substance. Therefore, acids are proton donor whereas bases are proton acceptor.

Conjugate Acid-Base Pairs

Consider a reaction

Acid1 + Base2 → Acid2 + Base1

H2O + HCl ⇔ H3O+ + Cl–

In this reaction, HCl donates a proton to H2O and is, therefore an acid. Water, on the other hand, accepts a proton from HCl, and is, therefore, a base. In the reverse reaction which at equilibrium proceeds at the same rate as the forward reaction, the H3O+ ions donate a proton to Cl– ion, hence H3O+, an ion is an acid. Cl– ion, because it accepts a proton fromH3O+ ion, is a base. Acid-base pairs in which the members of reaction can be formed from each other by the gain or loss of protons are called conjugate acid-base pairs.

Limitations of Bronsted Lowry Concept

Bronsted Lowry could not explain the reaction occurring in the non-protonic solvent like COCl3, SO2, N2O4, etc. It cannot explain the reactions between acidic oxides like etc and the basic oxides like etc which can easily take place in the absence of solvent as well e.g. (No proton transfer) Substances like BF3, AlCl3 etc, do not contain hydrogen which means they can’t donate a proton, still they behave as acids.

Bronsted-Lowry Theory of Acid and Base

Bronsted-Lowry Theory also provides an explanation of acid and base, according to this theory, acid is an H+ ion or a proton donor and it forms its conjugate base whereas the base is a substance that accepts an H+ ion or a proton to form conjugate acid.

Lewis Concept

According to Lewis theory of acid-base reactions, bases donate pairs of electrons and acids accept pairs of electrons. Thus, it can be said that a Lewis acid is electron-pair acceptor.

The advantage of the Lewis theory is that complements the model of oxidation-reduction reactions. Oxidation-reduction reactions take place on a transfer of electrons from one atom to another, with a net change in the oxidation number of one or more atoms.

The Lewis theory further suggested that acids react with bases and share a pair of electrons but there is no change in the oxidation numbers of any atoms. Either an electron is transferred from one atom to another, or the atoms come together to share a pair of electrons. Al(OH)3 + 3H+ → Al3+ + 3H2O (Aluminium hydroxide is acting as a base) Al(OH)3 + OH– → Al(OH)4- (Aluminium hydroxide is acting as an acid).

These reactions are showing clearly: When Aluminium hydroxide accepts protons, it acts as a base. When it accepts electrons, it acts as an acid. This Lewis acid-base theory also explains why non-metal oxides such as carbon dioxide dissolve in H2O to form acids, such as carbonic acid H2CO3.CO2(g) + H2O(l) → H2CO3(aq)

Limitations of Lewis Concept

Lewis concept gave a generalized idea including all coordination reactions and compounds. This is not true always. An idea about the relative strength of acids and bases is not provided by Lewis concept. Lewis concept is not in line with the acid-base reaction concept. Lewis concept has not discussed the behaviour of protonic acids like HCl.

Properties of Acids, Bases and Salts

Acids, bases and salts affect chemistry as well as our day to day life. They can be easily identified by their taste; that is acids taste sour and bases taste bitter and salts themselves have salty taste.

Acids are usually found in many substances including various food items but their presence in many fruits is very prominent, for example: Apart from these, there are some acids which are widely used in the laboratory, like hydrochloric acid, sulphuric acid and nitric acid.

Usually bases are found in household cleaners only to clean grease from the windows and the floors and it is also found in soaps, toothpaste, egg whites, dish washing liquids and household ammonia.

Our body contains some very common acids in the stomach like the dilute hydrochloric acid, which causes food indigestion. When the contents of our stomach become too acidic, we usually get indigestion and a burning sensation in our stomach.

Acids and bases also regulate some metabolic activities in the human body through the process of equilibrium. Bee stings are acidic in nature while the wasp stings are alkaline in nature. All acids when reacted with metals generate hydrogen gas. Hydrogen is usually common to all acids. Acid + Metal = Salt + Hydrogen. Example: OH– + H+ ⇌ H2O

Similarly, strong bases have a higher concentration of OH– ions per unit volume in their aqueous solution whereas weaker bases have a lower concentration of OH– ions per unit volume in their aqueous solution. An example of a strong base is KOH and an example of a weak acid is CaO. The strength of Acids and Bases can easily be measured using a pH scale.

PH Scale

pH stands for Potential of Hydrogen and is defined as the logarithm of H+ ion concentration. The pH value of any substance or solution indicates whether it is acidic, neutral, or alkaline.

The term pH was first introduced by Soren Peter (Biochemist), in 1909. To determine the strength of acids and bases, we use a universal indicator that shows different colours at different concentrations of hydrogen ions in a solution. The value of pH is generally used to quantitatively determine the strength of acid and base.The equation used for calculating the pH: pH = -log [H+]

What is pH value?

To find the pH value of a component we use a pH scale. The pH scale has values from 0 to 14, where 0 indicates very acidic, and 14 indicates very alkaline. 7 is the centre of the scale if any solution has a pH value of 7, it means that the solution is neutral in nature. The values less than 7 indicated that the solution is acidic and values more than 7 indicate that the solution is alkaline.For more detail on pH read,

pH is used to measure the basicity and acidity of a solution. The amount of hydrogen ion concentration in a solution determines its pH. Mathematically, it is given by a formula, pH=-log[H+] The pH scale is used to measure the relative acidity and alkalinity of solutions. The neutral value pH depends on temperature it can be lower than 7 if the temperature increases above25°C.

pH Indicator

An indicator that determines whether a solution is acid or basic is known as a pH indicator. Generally, the indicator causes the colour of the solution or paper to change depending on the pH value. There are different types of indicators some are solid and some are liquid in nature. But, the most common indicators are found in the form of strips of paper, known as the Litmus paper. It changes its colour to red when added to an acidic solution and gives a blue colour when tested with a basic solution. Also, there are various other ways to make indicators at home.

Indicator

Indicators are chemical compounds which help to indicate the presence of acid or base in a chemical reaction. They possess different colours in acidic solutions and different colours in basic solutions. Indicators are made naturally by plants and animals or artificially by humans. The image shows a litmus test of acids and bases.

An indicator indicating the pH

The range of 0 to 7 indicates an acidic solution. The range of 7 to 14 indicates the basic solution. 7 is a neutral solution.

Types of Indicators

There are various types of indicators used for various purposes some of which are,

Natural Indicators: Indicators derived from plants, animals or any living organism are natural indicators. Examples, Red Cabbage, Litmus paper and others.

Synthetic Indicators: Indicators made artificially in laboratories and factories are synthetic indicators. Examples, are Phenopthelien, Methyl orange, and others.

Olfactory Indicators: Substances that have different smells in acidic or basic mediums are called Olfactory Indicators. Example onions, olives and others.

Importance Of pH in Everyday Life

Digestive System: In the human body, all the physiological reactions take place at the pH of 7 – 7.8. Hydrochloric acid is secreted as food enters the stomach(turns the pH of the stomach between 1 and 3) because of overeating or various reasons excess of HCl (hydrochloric acid) is released. The excess of HCl in the stomach causes indigestion which produces pain and irritation (pH level of the stomach decreases). To cure indigestion, we can take bases called antacids (anti-acid). Antacids are a group of mild bases. Being basic in nature, they react with excess acid in the stomach and neutralise it. (which have no toxic effects on our body) Common antacids used for curing indigestion due to acidity are:-

Milk of Magnesia (Magnesium hydroxide) Mg(OH)2(s) + 2HCl(aq) → 2H2O(l) + MgCl2(aq) Baking Soda (Sodium hydrogen carbonate) NaHCO₃ + HCl ➝ NaCl + CO₂ + H₂O

Tooth Decay

When we eat food, the bacteria present in our mouths break down the sugar to form acids. The acid lowers the pH in the mouth making it acidic. When the pH of the mouth falls below 5.5, our tooth starts decaying. Tooth Decay happens because the acid becomes strong enough to attack the enamel (of our teeth) and corrode it. The best way to prevent tooth decay is to clean the mouth thoroughly after eating food. Many kinds of toothpaste contain bases to neutralise mouth acid (The pH of toothpaste being about 8.0). So using toothpaste for cleaning the teeth can neutralise the excess acid in the mouth.

Plants and Animals are Sensitive to pH changes

Most of the plants grow best when the pH of the soil is close to 7. If the soil is too acidic (low pH), then it is treated with:- Quicklime (Calcium Oxide). Slaked lime (Calcium Hydroxide). Chalk (Calcium Carbonate).

If the soil is too alkaline then it can be reduced by adding Manure or Compost (decaying organic matter) which contains acidic materials. The pH also plays an important role in the survival of animals, including human beings. The aquatic animals can survive in water bodies within a narrow range of pH change. The high acidity of water bodies can kill aquatic animals. Calcium Carbonate is often added to acidic lake water to neutralise the acid that comes from acid rain.

Self Defiance by Animals and Plants through Chemical Warfare: When a honey bee stings a person, it injects Formic Acid into the skin. By rubbing a mild baking soda neutralises the acidic liquid injected by a bee sting. When a wasp stings, it injects an alkaline liquid (Methanoic Acid(HCOOH)) into the skin causing burning pain. By rubbing mild acid vinegar on the stung area gives relief. When a person touches the leaves of a nettle plant, the stinging hair of nettle leaves injects Methanoic Acid into the skin. It can be neutralized by rubbing Baking Soda or Dock Plant which grows beside the nettle plant and is basic in nature.

HCOOH + NaHCO3 ⟶ HCOONa + CO2 + H2O

Lemon juice to clean copper vessels A dull green coloured film forms on a copper vessel when it is exposed to damp air over an extended period of time. Copper hydroxide (Cu(OH)2) and copper carbonate (CuCO3) are combined to form this greenish layer. The reaction is, 2Cu + H2O + CO2 + O2 ⟶ Cu(OH)2 + CuCO3

Because these goods are basic in nature, acidic substances such as lemon or tamarind juice are required to clean them. These sour compounds are chosen for cleaning since they are good at cleaning copper vessels.

Acids and Bases React with Metals?

When acids react with metal, they release hydrogen gas and create a compound called Salt. Acid + Metal = Hydrogen gas + Salt

When base reacts with metal, they release hydrogen gas and produce salt. When sodium hydroxide reacts with zinc metal then it releases hydrogen gas and gives sodium zincate. 2NaOH(aq) + Zn(s) → Na2ZnO2 (s) + H2 (g) (Sodium zincate)

Metal Hydrogen carbonates react with Acids:

We now move on to understand the reaction of metal carbonates and hydrogen carbonates with acids in acids, bases and salts class 10. All Metal Carbonates and Metal Hydrogen Carbonates react with Acids to produce its corresponding salt, carbon dioxide and water. Metal carbonate/Metal hydrogen carbonate + Acid = Salt + Carbon dioxide + Water For instance, when Sodium Carbonate is mixed with Hydrochloric Acid, it produces Sodium Chloride + Carbon dioxide + Water. Na2CO3 (S) + 2HCl(aq) → 2NaCl(aq) + CO2 (g) + H2O(I)

React With Each Other: When an acid reacts with a base, they tend to nullify each other’s effects. This is called a neutralisation reaction because both substances have a neutralising effect on each other. A reaction between an acid and base results in the production of salt and water. Acid + Base = Salt and Water.For instance, when sodium hydroxide is diluted with hydrochloric acid then it gives sodium chloride and water. NaOH + HCl = NaCl + H2O

Metallic Oxides React With Acids: When metal oxide (also called basic oxides) reacts with acids, they nullify each other and give rise to its corresponding salt and water. For instance, if copper oxide is diluted with hydrochloric acid, the solution turns bluish-green in colour and results in the formation of copper(II) chloride along with water: CuO + 2HCI = CuCI2 + H2O

Non-Metallic Oxides react with Bases: we look at the reaction of non metallic oxides with bases. Non- metallic oxides are acidic in nature which means that when a base reacts with non-metal oxide, it nullifies the effect and produces salt and water. When calcium hydroxide (base) reacts with carbon dioxide (non-metallic oxide), it produces salt and water.

Salts:

Apart from sodium chloride, other common salts are sodium nitrate, barium sulfate etc. Sodium chloride or common salt is a product of the reaction between the hydrochloric acid (acid) and sodium hydroxide (base). Solid sodium chloride is made of a cluster of positively charged sodium ions and negatively charged chloride ions held together by electrostatic forces.

Electrostatic forces between opposite charges are inversely proportional to the dielectric constant of the medium. In other words, we can say that a compound that has acidity in its nature and a compound that has basicity as its nature, may yield salts when combined together.

he universal solvent, water, has a dielectric constant of 80. Therefore, when sodium chloride is dissolved in water, the dielectric constant of water reduces the electrostatic force, allowing the ions to move freely in the solution. They are also well-separated due to hydration with water molecules.

What are Salts?

When an acid and a base react to neutralize one another, they generate sales, which are ionic substances. Salts do not have an electrical charge. Salts come in a variety of forms, the most common of which is sodium chloride. Table salt and common salt are both terms for sodium chloride. Sodium chloride is used to make dishes taste better.

Physical Properties of Salt

Salts have various physical properties and some of following physical properties of salts are,

In nature, the bulk of the salts is crystalline. Salts that are transparent or opaque are available. The bulk of salts is soluble in water. Salt solutions, in their molten state, also transmit electricity. The flavour of salt can be salty, sour, sweet, bitter, or umami (savoury). There is no odour to neutral salts. Salts that are colourless or coloured are available. Because it contains ions, salt water is an excellent conductor of electricity. Electrostatic attraction holds the ions together, and a chemical bond is established between them.

Salts are formed by the combination of acid and base through the neutralization reaction. The acidic and basic nature of salts usually depends on the acid and base from which the salt evolved in a neutralization reaction.

Example:NaOH+HCl→NaCl+H2O HCl + NH4OH → NH4Cl + H2 CH3COOH + NaOH → CH3COONa + H CH3COOH + NH4OH → CH3COO NH4+ H2O The most well-known or common salt is sodium chloride or table salt which is formed by the combination of a strong base sodium hydroxide and strong acid hydrochloric acid. HCl(aq)+NaOH(aq)→NaCl(aq)+H2O(l)

Other examples include Epsom salt (MgSO4) which is used in bath salts, ammonium nitrate (NH4NO3) is used as fertilizer, and baking soda (NaHCO3) is used in cooking. The pH of a solution of salt also depends on the strength of acids and bases which are combined in the neutralization reaction.

Types of Salts

Salts are categorised into various categories some of the important categories are given below: Acidic Salt, Basic or Alkali Salt, Neutral Salts

Acidic Salt: A partial neutralisation of a diprotic or polyprotic acid produces an acidic salt. These salts contain H+ cations or strong cations in their aqueous solution. The ionizable H+ makes up the majority of the ions. Some examples of acidic salts are NaHSO4­, KH2PO4 etc. These salts are formed by the neutralization of strong acids and weak bases.

Ammonium Chloride: Ammonium chloride is formed when hydrochloric acid (a strong acid) interacts with ammonium hydroxide (a weak base). NH4OH + HCl → NH4Cl + H2O

Ammonium Sulphate: Ammonium sulphate is formed when ammonium hydroxide (a weak base) reacts with sulphuric acid (a strong acid). 2NH4OH + H2SO4 → (NH4)2SO4 + 2H2O

Basic or Alkali Salt: A basic salt is formed when a strong base reacts with a weak acid to partially neutralise it. When they are hydrolyzed, they decompose into a basic solution. This is because when a basic salt is hydrolyzed, it produces the conjugate base of a weak acid in the solution. e.g. Sodium Carbonate (Na2CO3), Sodium Acetate (CH3COONa)

Sodium Carbonate: Sodium carbonate is formed when sodium hydroxide (a strong base) reacts with carbonic acid (a weak acid) H2CO3 + 2NaOH → Na2CO3 + H2O

Sodium Acetate: Sodium acetate is formed when a strongly basic, sodium hydroxide (a strong base), reacts with acetic acid (a weak acid) CH3COOH + NaOH → CH3COONa + H2O

Neutral Salts

Salts generated by the reaction of a strong acid with a strong base are neutral in nature. The pH of these salts is 7, which is considered neutral. Potassium Chloride, Sodium Chloride, and others are examples of neutral salts.

Sodium Chloride (NaCl): Sodium Chloride is formed when hydrochloric acid (a strong acid) mixes with sodium hydroxide (a strong base). NaOH + HCl → NaCl + H2O

Sodium Sulphate (Na2SO4): It’s made when sulphuric acid combines with sodium hydroxide (a strong basic) ( a strong acid). 2NaOH + H2SO4 → Na2SO4 + 2H2O

Salts can also be categorised into other categories which include, Mixed Salts & Double Salt

Double Salt: Salts with more than one cation or anion are known as double salts. They’re created by mixing two different salts that crystallised in the same ionic lattice. e.g. Potassium Sodium Tartrate (KNaC4H4O6.4H2O) also known as Rochelle salt.

Mixed Salts: Salts which are produced by mixing two salts, which generally share a common cation or anion, are called mixed salt. e..g. Bleaching Powder CaOCl2.

Formation of Acidic, Basic, and Neutral Salts

The causes of the formation of Acidic, Basic, and Neutral Salts are discussed below,

When a strong acid reacts with a weak base, the base is unable to completely neutralise the acid. As a result, a salt that is acidic forms.

When a strong base is combined with a weak acid, the acid is unable to completely neutralise it. As a result, you get a simple salt.

When an equal-strength acid and base react, they totally neutralise each other. A neutral salt is formed as a result of this process.

Some Common Salts

Salts are chemical compounds that are formed as a result of a neutralization reaction between acids and bases. When we hear salt we only think about common salt which is Sodium chloride that we eat in our daily life but there are several other salts also which are widely useful. Here in this article, we will learn about some common salt that is widely used. Baking Soda or Sodium Bicarbonate. Washing Soda or Sodium Carbonate. Bleaching Powder or Calcium Hypochlorite

Baking Soda

Baking soda also called Sodium Hydrogen Carbonate, is a chemical compound whose chemical formula is NaHCO3. Baking soda has a sodium cation (Na+) and a bicarbonate anion (HCO3–). Sodium bicarbonate is a white, crystalline powder and as the name suggests is used for baking.

Chemical Name: Sodium hydrogen carbonate

Chemical Formula: NaHCO3

Preparation: Baking soda can be prepared with the help of the reaction given below. NaCl(aq) + NH3(g) + CO2(g) + H2O(l) → NaHCO3(aq) + NH4Cl(aq)

Uses: A few of the uses of Baking Soda are, It is used as an antacid in case of acidity. It is used for baking purposes. It is used as a water softener.

Washing Soda

Washing soda also called Sodium Carbonate, is a chemical compound whose chemical formula is Na2CO3. Washing soda has two sodium cations (Na+) and a carbonate anion (CO32-). Sodium carbonate is a white, crystalline powder and as the name suggests is used for washing purposes.

Chemical Name: Sodium Carbonate

Chemical Formula: Na2CO3

Uses: A few of the uses of Washing Soda are,

It is used in the glass, soap and paper industries. It is used as washing powder.

Bleaching Powder

Bleaching Powder also called Calcium Hypochlorite, is a chemical compound whose chemical formula is CaOCl2. Bleaching Powder is used for bleaching purposes. In its aqueous solution bleaching powder releases chlorine which is responsible for the bleaching action.

Chemical Name: Calcium Hypochlorite

Chemical Formula: CaOCl2

Preparation: Bleaching Powder can be prepared with the help of the reaction given below.

Ca(OH)2(aq) + Cl2(g) → CaOCl2(aq) + H2O(l)

Uses: A few of the uses of Bleaching Powder are, It is used for bleaching the laundry. It is used as an oxidizer in many industries. It is used as a disinfectant to clean water

Crystals of Salts

Some salts combining with water form crystals and these water molecules which are required to form crystals are called water of crystallisation. Some examples of crystal salts are Table salt (sodium chloride crystals), Sugar (sucrose crystals).

Plaster of Paris

Plaster of Paris is a widely used chemical compound is used for various purposes such as sculpting materials, gauze bandages, building and furnishing houses and others. Plaster of Paris is hydrated calcium sulphate obtained by calcining gypsum. It is a white powdery chemical compound.Chemical Name: Calcium Sulphate Hemi Hydrate.

Chemical Formula: CaSO4. ½ H2O

Preparation of Plaster of Paris: Plaster of Paris can easily be prepared with the help of the equation given below, CaSO4.2H2O (s) (heating at 100°C ) —> CaSO4. ½ H2O + 3/2 H