VERY SHORT ANSWER -Class 10 – Science -Chemistry -chapter 2- Acids, Bases and Salt

VERY SHORT ANSWER -Class 10 – Science -Chemistry -chapter 2- Acids, Bases and Salt

Q1. Three acidic solutions A, B and C have pH = 0, 3 and 5 respectively. a. Which solution has the highest concentration of H+ ions? b. Which solution has the lowest concentration of H+ ions? 

Ans :  a. The solution with pH = 0 has highest concentration of H+ ions.

 b. The solution with pH = 5 has lowest concentration of H+ ions.

Q2. 15 mL of water and 10 mL of sulphuric acid are to be mixed in a beaker
(i) State the method that should be followed with reason.
(ii)What is this process called?
Ans:
(i) The acid is to be added slowly in water to prevent the mixture to be splashed. The
reaction is highly exothermic; therefore, constant cooling should be done.
(ii)The process is called dilution.

Q3. Explain how antacid works.
Ans. Hyperacidity is caused by excess of hydrochloric acid in stomach. Antacid is basic in nature. It neutralizes excess of acid and gives relief from pain caused by hyperacidity.

Q4. A compound ‘X’ of sodium is commonly used in Kitchen for making crispy pakoras. It is also used for curing acidity in the stomach.
Identify ‘X’. What is its chemical formula? State the reaction that takes place when it is heated during cooking.

Ans: The compound ‘X’ is a constituent of baking powder. It is called baking soda.

Chemically, the compound is sodium hydrogen carbonate with the formula NaHCO3. Upon heating, the compound ‘X’ will release carbon dioxide gas.

2NaHCO3→Na2CO3(s)+H2O(l)+CO2(g)

Q5. What is baking powder? How does it make the cake soft and spongy?

Ans: Baking powder is a mixture of sodium hydrogen carbonate and tartaric acid. On heating it liberates CO2 which makes the cake soft and spongy.

Q6. What happens when a base reacts with a non-metallic oxide. What would you infer about the nature of the non-metallic oxide? 

Ans. A base reacts with a non-metal oxide to form salt and water. The non-metal oxide is, therefore, an acidic oxide. For example,

2 NaOH (aq) CO2 (g) ———> Na2CO3 (aq) + H2O (aq)

Q7. An old person complained of acute pain in the stomach. Doctor gave him a small antacid tablet and he got immediate relief. What actually happened? 

Ans. The old person was suffering from acute acidity. Antacid tablets contain sodium hydrogen carbonate (NaHCO3). It reacts with the acid (HCl) formed because of acidity and neutralizes its effect. That is how the old person got relief.

Q8. The oxide of a metal M was water soluble. When a blue litmus strip was dipped in this solution, it did not undergo any change in colour. Predict the nature of the oxide. 

Ans. The metal oxide (MO) is of basic nature. It dissolves in water to form metal hydroxide as follows :

MO + H2O → M(OH)2

A blue litmus does not undergo any change in colour in the basic medium. 

Q9. Why distilled water not conducts electricity? When rain water conducts electricity.

Ans: Distilled water cannot conduct electricity because it does not contain ions while rain water conducts electricity as it contains ions due presence of dissolved salts in it.

Q10. Why alkalis like sodium hydroxide and potassium hydroxide should not be left exposed to air?

Ans. Alkalis should not be left exposed to air because they are hygroscopic in nature  and absorb moisture from atmosphere in which they get dissolved.

Q11. Fresh milk has a pH of 6. What will be the PH value if milk changes into a curd Justify.

Ans. When milk changes into a curd, its PH value decreases i.e. lactose gets converted into lactic acid. As more of acid is formed, its PH value decreases.

Q12. Why does an aqueous solution of an acid conduct electricity?

 Ans. Electricity is conducted in a solution by ions. Acid release H+ ions in a solution so, it conducts electricity.

Q13. You have two solutions ‘A’ and ‘B’. The pH of solution ‘A’  is 6 and pH of solution ‘B’ is 8. Which        solution has more hydrogen ions concentration? Which is acidic and which one is basic?

 Ans. A solution having pH less  than 7 is acidic and that having  pH more than 7 is basic. So, solution ‘A’ is acid and ‘B’ is basic. Naturally ‘A      ‘ which is acidic  has greater concentration of hydrogen ions concentrations.

Q14. Plaster of Paris should be stored in moisture-proof container. Explain why?

Ans. Plaster of Paris reacts with moisture to form gypsum and sets to a hard mass. Therefore, it should be stored in moisture-proof container.

Q15. A few drops of phenolphthalein indicator were added to an unknown solution A. It Acquired pink colour. Now another unknown solution B was added    to it drop by Drop and the solution becomes colourless. Predict the nature of A & B.

 Ans. Sol ‘A’ is basic in nature as phenolphthalein has imparted pink colour to it. Sol ‘B’ is an acid it has made solution A colourless by neutralizing by its basic effect.