Class 10 Solutions Acids,Bases And Salts

1.Complete and balance the following chemical equations :
(a) Zn (s) + HCl (aq) ——- >
(b) Na2C03 (s) + HCl (aq) ———>
(c) NaHC03 (s) + HCl (aq) ——–>
(d) NaOH (aq) + HCl (aq) ———>
(e) CuO(s) + HCl (aq) ———->

Solution :

2.Fill in the blanks in the following sentences :
(a) Acids have a…………….. taste and they turn…………… litmus to……………….
(b) Substances do not show their acidic properties without……………….
(c) Acids produce…………… ions on dissolving in water.
(d) Those substances whose smell (or odour) changes in acidic or basic solutions are called
(e) Onion and vanilla extract are…………..
Solution :
(a) Sour; blue; bed.
(b) Water.
(c) Hydrogen.
(d) Olfactory.
(e) Olfactory.

3.(a) What is an indicator ? Name three common indicators.
(b) Name the acid-base indicator extracted from lichen.
(c) What colour does the turmeric paper turn when put in an alkaline solution ?
Solution :
(a) An indicator is a ‘dye’ that changes colour when it is put in an acid or a base. The three most common indicators are: Litmus, Methyl orange and Phenolphthalein.
(b) Litmus.
(c) Red.

4.What is an olfactory indicator ? Name two olfactory indicators. What is the effect of adding sodium hydroxide solution to these olfactory indicators ?
Solution :
Those substances
whose smell (or odour) changes in acidic or basic solutions are called olfactory indicators. Onion and vanilla extracts are olfactory indicators. When a basic solution like sodium hydroxide solution is added to a cloth
strip treated with onions (or onion extract), then the onion smell cannot be detected.

5.(a) What happens when an acid reacts with a metal ? Give chemical equation of the reaction involved.
(b) Which gas is usually liberated when an acid reacts with a metal ? How will you test for the presence of this gas ?
Solution :
(a) When an acid reacts with a metal, then a salt and hydrogen gas are formed.

(b) Hydrogen gas is liberated when an acid reacts with a metal. When reaction between an acid and a metal occurs, we observe formation of gas bubbles. When these gas bubbles are passed through soap solution, gas filled soap bubbles rise into the air. When a burning candle is brought near a gas-filled soap bubble, the gas present in the soap-bubble burns with a ‘pop’ sound. Only hydrogen gas burns making a ‘pop’ sound. This shows that hydrogen gas is evolved in the process.

6.While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid ?
Solution :
When a concentrated acid is added to water for preparing a dilute acid, then the heat is evolved gradually and easily absorbed by the large amount of water (to which the acid is being added) however if water is added to concentrated acid, then large amount of heat is evolved at once. This heat changes some of the water to steam explosively which can splash the acid on our face or clothes and causeacid burns. Even the glass container may break due to the excessive heating.

7.What happens when an acid reacts with a metal hydrogencarbonate ? Write equation of the reaction which takes place.
Solution :
When an acid reacts with a metal hydrogen carbonate, then a salt, carbon dioxide gas and water are formed.