1. ACID, BASES AND SALTS
1 A white powder is added while baking breads and cakes to make them soft and fluffy.
Write the name of the powder? Name the main ingredients in it? Write the equation for the
chemical reaction takes place when the powder is heated during baking?
Ans. White powder is Baking powder. The main ingredients are sodium hydrogen
carbonate (sodium bicarbonate) and tartaric acid.
The chemical reaction is
2NaHCO3-----Heat----------- Na2CO3 + CO2+ H2O
CO2 released makes the bread and cakes soft and fluffy.
Q2. While diluting an acid, why is it recommended that the acid should be added to water and
not water to the acid?
Ans. When water is added to acid ,the reaction is highly exothermic. So
(a) the acid may splash (b)it may cause burns and (c) even the bottle/container can break. To avoid
this is it recommended that the acid should be added to water.
Q3 Fresh milk has pH of 6. How do you think the pH will change as it turns into curd?
Explain your answer.
Ans. When milk is turned in to curd then its pH value will decrease. This is due to the
formation of lactic acid. The increase in acidic character is nothing but decrease in pH value.
The curd is acidic as the microbes initiate the formation of lactic acid.
4. Dry pellets of a base ‘X’ when kept in open absorbs moisture and turns sticky. The
compound is also formed by chlor-alkali process. Write chemical name and formula of ‘X’.
Describe chlor-alkali process with a balanced chemical equation.
Ans. ‘X’ is Sodium hydroxide (NaOH)
When sodium chloride solution (brine solution) is electrolysed, sodium hydroxide solution is formed
along with the liberation of chlorine and hydrogen gas. This process is called chlor-alkali process.
2NaCl + 2H2O----------------- 2NaOH + Cl2 + H2
5. A white coloured powder is used by doctors for supporting fractured bones. (a) Write
chemical name and formula of the powder. (b) When this white powder is mixed with water a
hard solid mass is obtained. Name the compound and Write balanced chemical equation for
it.
Ans. a) Calcium Sulphate Hemihydrate {also known as Plaster of Paris}
CaSO4 ·1/2 H 2 O (b) Gypsum
2. (b) Ca SO4 . ½ H2 O + 11
/2 H2 O → Ca SO4 . 2 H2O
6.What is meant by pH value of a solution? What happens to pH value of
a) An acid (HCl) solution, when it is diluted with water.
b) An alkali (NaOH) solution ,when it is diluted with water.
Ans. The acidity or alkalinity of a solution is expressed in terms of pH.
a) When the solution of an acid is diluted by mixing more water in it, the
concentration of hydrogen ions (H+–
ions) per unit volume decreases .
b) When the solution of a base is diluted by mixing more water in it, the
concentration of hydroxide ions (OH–
ions) per unit volume decreases.
7. What is washing soda?State its two important properties and two important
uses.
Ans. Washing sodais Sodium carbonate decahydrate.
Properties :--1. When freshly prepared, it is a transparent crystalline solid.
2. On exposure to air, it decomposes to form monohydrate which
is a white powder.
Uses:--1. It is used in laundry.
2. It is used to remove the permanent hardness of water.
8. A calcium compound having an odourof chlorine is used to remove
yellowness
of white cloths in laundries
a) Name this compound
b) Write its chemical formula and chemical name
c) Write the chemical equation involved in its preparation.
Ans. a) Bleaching powder
b) Calcium oxy chloride - CaOCl2
c) Ca(OH)2 + Cl2----------------- CaOCl2 + H2O
9. Generally hydrogen gas is prepared by the action of dilute sulphuric acid and
zinc granules. A student used
3. a) Zinc dust in place of zinc granules b) Dilute HCl in place of dilute H2SO4.
What changes he will observe?
Ans. a) The reaction will be comparatively faster and hydrogen gas will evolve
with great speed. Because zinc dust has more surface area than granules.
b) Zinc metal displaces the hydrogen to form hydrogen gas and zinc chloride, a
salt. Zinc reacts quickly with the acid to form bubbles of hydrogen.
10. Classify the following into weak acid, strong acid, weak base, and strong
base.
i) H2SO4 ii)HNO3 iii)CH3COOH iv) NaOH v)KOH vi) NH4OH
Ans :
Weak acids -- CH3COOH
Strong acids -- H2SO4 , HNO3
Strong base -- NaOH , KOH
Weak base -- NH4OH
