Acids, Bases And Salts

1 M HCl has a higher concentration of H⁺ ions than 1 M CH₃COOH because HCl is a strong acid then CH₃COOH hence 1M HCL produces more amount of H⁺ ions than that produced by 1 M CH₃COOH.

1 M HCl solution have a higher concentration of H⁺ ions than 1 M CH₃COOH solution because HCl is a strong acid than CH₃COOH. Hence the H in HCl is able to dissociate very quickly from its formula unit mass and gets liberated in the form of H⁺ very quickly leading to a rapid increase in the H⁺ concentration but CH₃COOH is a weak acid and the H present in it is not able to dissociate quickly and completely from its formula unit mass in the form of H⁺ ionswhich leads to a slow increase in the H⁺ ion concentration and a low concentration of H⁺ ions in the solution.

The common name of the compound CaOCl₂ is bleaching powder. It is used as a bleaching agent for bleaching cotton, linen, wood pulp, clothes, as an oxidizing agent in chemical industry and for disinfecting drinking water.

Dry slaked lime [Ca(OH)₂] on treatment with chlorine yields bleaching powder.

The chemical equation representing its formation is: -

Ca(OH)₂ + Cl₂→ CaOCl₂ + H₂O

The sodium compound which is used for softening hard water is called sodium carbonate which is most commonly known as washing soda. It is prepared by heating baking soda and then recrystallizing the product so obtained to get washing soda.

a. Marble is chemically composed of calcium carbonate (CaCO₃). According to the question, the student dropped few pieces of marble in dilute HCl contained in a test tube. We know that acids react with calcium carbonate to form or give the corresponding salt, carbon dioxide and water. Hence, when we pass the carbon dioxide gas through lime water a white precipitate would be observed to form in the test tube containing the lime water.

b. The balanced chemical equation for the above change when we pass the carbon dioxide gas through lime water is : -

Ca(OH)₂(aq) + CO₂(g) → CaCO₃(s) + H₂O(l)

The colour of FeSO₄.7H₂O crystals is light green. Upon heating the crystals of FeSO₄.7H₂O losses water of crystallization and becomes white in colour,

Balanced chemical equation for the change is: -

2FeSO₄ Fe₂O₃ + SO₂ + SO₃

a. The acid present in tomato is oxalic acid.

b. The acid present in vinegar is acetic acid.

c. The acid present in tamarind is tartaric acid.

a. The bases which are soluble in water are called alkali.

Sodium hydroxide is a base which is soluble in water and hence it is an alkali.

b. A compound is said to be acidic in character if it is able to generate H⁺ ions in aqueous solutions. HCl, HNO₃, etc. show acidic characters in aqueous solutions because they are able to generate H⁺ ions in aqueous solutions while solutions of compounds like alcohol and glucose do not show acidic character because they are not able to generate H⁺ ions in aqueous solutions

a. The chemical name and formula of the white coloured powder which is used by doctors for supporting fractured bones is : -

Chemical name – Calcium sulphate hemihydrate

Formula - CaSO₄.H₂O

b. When this white powder is mixed with water a hard-solid mass is obtained. The balanced chemical equation for the change is : -

CaSO₄.H₂O + 1 H₂O CaSO₄.2H₂O

Chlorine gas reacts with lime water to form bleaching powder which is used as a bleaching agent in chemical industry.

Hence, the species X is Chlorine gas and the species Y is Bleaching powder with formula -CaOCl₂.

The chemical equation of the reactions involved is : -

Ca(OH)₂ + Cl₂→ CaOCl₂ + H₂O

a. The compound which is prepared from gypsum which has the property of hardening when mixed with proper quantity of water is called plaster of Paris having the formula - CaSO₄.H₂O.

b. The chemical equation for the preparation of plaster of Paris is : -

CaSO₄.2H₂O CaSO₄.H₂O

Plaster of Paris is prepared by heating gypsum at 373K.

c. One of the important use of plaster of Paris is that it is used by doctors as a plaster for supporting fractured bones in the right position

i. When hydrochloric acid reacts with sodium carbonate the following reactions takes place : -

Na₂CO₃(s) + 2HCl (aq) → 2NaCl(s) + H₂O (l) + CO₂ (g)

Hence, when an acid reacts with a metal carbonate the corresponding salt is formed along with the evolution of carbon dioxide gas and the formation of water.

ii. When hydrochloric acid reacts with sodium hydrogen carbonate the following reactions takes place : -

NaHCO₃(s) + HCl (aq) → NaCl(s) + H₂O (l) + CO₂ (g)

Hence, when an acid reacts with a metal hydrogen carbonate the corresponding salt is formed along with the evolution of carbon dioxide gas and the formation of water.

iii. When dilute hydrochloric acid reacts with copper oxide the following reactions takes place : -

CuO(s) + 2HCl (aq) → 2CuCl₂(s) + H₂O (l)

Hence, when an acid reacts with a metal oxide the corresponding salt is formed along with the formation of water.

This reaction could be seen as similar to the reaction between an acid and a base. So, metallic oxides are treated as basic in nature.

b. According to the theory on a pH scale, a more acidic substance is assigned a lower value. Normally substances with pH less than 7 are considered as acidic and those with pH greater than 7 are considered as basic with acidic strength increasing as we move towards 1 from 7 and the basic strength increases as we move toward 14 from 7. The more the acidic a substance is the more the hydrogen ions concentration will be.

Hence, in the given solutions, solution A has more hydrogen ions concentration as it is having the least pH value out of the three.

The nature of each solution is: -

Solution A – acidic

Solution B – basic

Solution C – basic

Given that the metal compound ‘X’ reacts with dil.H₂SO₄ to produce effervescence and the gas evolved extinguishes a burning candle. Now, since the gas evolved extinguishes the candle it must be carbon dioxide. It is also given that one of the compounds formed is calcium sulphate, hence the metal compound X is calcium carbonate.

Hence, the reaction between calcium carbonate and dil.H₂SO₄ is as follows: -

CaCO₃ + H₂SO₄→ CaSO₄ + CO₂ + H₂O

i. Name of one antacid is Magnesium

Hydroxide (Milk of magnesia).

During indigestion, our stomach produces too much acid and this causes irritation. Hence, when we take a base it neutralises the effect of the excess acid and relieves us from the irritation and indigestion.

ii. Quicklime or calcium carbonate is basic in nature. Hence, the nature of the soil must be acidic.

Plants grow well in the pH range of 6 – 8. So, when the soil becomes acidic in nature the farmers add bases like quicklime or calcium carbonate to neutralise the excess acid and maintain the pH.

a. If in the place of zinc granules, same amount of zinc dust is taken in the test tube then the rate of the reaction will increase and the reaction will take place more quickly. This is because the surface area per unit volume of powder is more than that of the zinc granules and hence the powder will provide more surface area for the reaction to take place.

b. If in place of dilute sulphuric acid, we use dilute hydrochloric acid then the reaction will take place as usual because in both the cases we are mixing a strong acid with a metal.

c. If in place of zinc, copper turnings are taken then also the reaction will proceed in a similar way and would lead to the evolution of hydrogen gas as here we are only replacing one metal with another metal in the reactant side of the reaction. In this case, also we are mixing a strong acid with a metal.

d. If sodium hydroxide is taken in place of dilute sulphuric acid and the tube is heated then the metal will react with the base to form the corresponding salt and will evolve hydrogen gas as per the following reaction:-

Zn + 2NaOH → Na₂ZnO₂ + H₂

a. The common salt that we use in your food is obtained by the combination of base - sodium hydroxide (NaOH) and the acid - hydrochloric acid (HCl).

The formula for the common salt that we use in your food is NaCl and its name is sodium chloride.

It is obtained from seawater.

b. When the seas of bygone ages dried-up beds of rock salt were being formed. Rock salts are the deposits of solid salts.

The colour of rock salt is brown. It is brown in colour due to the impurities present in it.

c. When electricity is passed through brine it decomposes to form sodium hydroxide along with the evolution of chlorine gas at anode and hydrogen gas at cathode. Sodium hydroxide solution is also formed near the cathode.

The chemical equation for the above decomposition is: -

2NaCl (aq) +2H₂O (l) 2NaOH (aq) + Cl₂ (g) + H₂ (g)

(a) The compound of calcium which is a yellowish white powder and is used for disinfecting drinking water is CaOCl₂ commonly known as bleaching powder.

Its chemical name is – Calcium oxychloride

Formula - CaOCl₂

Ca(OH)₂ + Cl₂→ CaOCl₂ + H₂O

Two other uses of the compound are:-

1. It is used as an oxidising agent in many chemical industries.

2. It is used for bleaching cotton and linen in the textile industry, wood pulp bleaching and for bleaching washed clothes in the laundry.

(b) The balanced chemical equation of chlor-alkali process is : -

2NaCl (aq) +2H₂O (l) → 2NaOH (aq) + Cl₂ (g) + H₂ (g)

a) Crystals of a substance which changed their colour on heating in a closed test tube but regained it after sometime when they were allowed to cool down are copper sulphate or more specifically hydrated copper sulphate.

Its formula is – CuSO₄.5H₂O

The phenomena involved is due to the presence of molecules of water of crystallization in the molecule. Water of crystallization is the fixed number of water molecules that are present in one formula unit of a salt. When we heat the crystals of hydrated copper sulphate this water is removed and the salt turns white. But when it is allowed to cool down in open air then it regains its lost water of crystallization and hence regains its colour also.

b) The compound whose one formula unit is associated with 10 water molecules is sodium carbonate (Na₂CO₃. 10H₂O) commonly known as washing soda.

It is prepared by heating baking soda and then recrystallizing the product so obtained.

The equations related to the above reaction is: -

2NaHCO₃ Na₂CO₃ + H₂O + CO₂

Na₂CO₃ + 10H₂O → Na₂CO₃. 10H₂O

Two uses of washing soda are: -

1. It is used in glass, soap and paper industries

2. It is used for removing permanent hardness of water.

a. Sulfuric acid, sulphurous acids are formed by sulphur dioxide in presence of air.

b. Nitric acid is formed by nitrogen dioxide in presence of air.

c. Plants, agricultural crops and trees require an optimum pH for their survival. Due to acid rain, the pH balance of the soil is disturbed and the soil becomes more acidic. This acidic nature of the soil is very much harmful to the healthy growth of plants, agricultural crops and trees. In this way, acid rain is harmful to agriculture, trees and plants.

d. We can prevent acid rain by controlling pollution, by controlling the rate of consumption and burning of fossil fuels such as coal and petroleum oil, by controlling automobile combustion, reducing the burning of wastes, filtering out particulate matters emitted from the industries, using cleaner fuels like CNG in the automobiles and start using renewable sources of energy like solar energy, wind energy, tidal energy etc for electricity generation.

e. Hritik possesses the value of social responsibility. He is very much concerned for his environment and the health of the society as a whole.