CBSE Class 10 Chapter 2 Acids, Bases and Salts In-text Questions Answer

 CBSE Class 10 Chapter 2 Acids, Bases and Salts  In-text Questions Answer 

Q1

You are given three test tubes. The three test tubes contain distilled water, an acidic solution and the basic solution, respectively. There is only red litmus paper available in order to identify what is there in each test tube. How will you find out what is in each of the test tubes?

Ans

Yes, I can identify the solution in each of the test tubes through red litmus paper by following method: Use each of the three solutions from the test tubes onto separate red litmus papers. If the solution turns the red litmus to blue, it contains a basic solution. Take the blue litmus paper formed in the previous step and split it into two parts. If the solution from the test tube turns the blue litmus paper back to red, it is the acidic solution. If the solution from the test tube doesn't make any change in litmus paper, it contains distill water.

 

Q2	Why should curd and sour substances not be kept in brass and copper vessels?
Ans	Curd and sour substances should not be kept in brass and copper vessels because they can react with the metals, leading to a metallic taste, potential copper contamination and health risks due to copper toxicity.

 

Q3

Which gas is usually liberated when an acid reacts with a metal? Illustrate with an example. How will you test for the presence of this gas?

Ans

When an acid reacts with a metal, hydrogen gas (H2) is usually liberated. This reaction is known as a metal-acid reaction. The general chemical equation for this reaction is: Metal + Acid → Salt + Hydrogen Gas Example:                  Zn + 2HCl → ZnCl2 + H2 In this reaction, zinc reacts with hydrochloric acid to produce zinc chloride (ZnCl2) and hydrogen gas (H2). To confirm the presence of hydrogen gas, we use "squeaky pop" test. For this test, We carefully collect some of the gas by inverting a test tube over the reaction mixture. When gas fills the test tube, carefully bring it near an open flame. If the gas is hydrogen, it will produce a characteristic "squeaky pop" sound when it ignites.

 

Q3

Metal compound A reacts with dilute hydrochloric acid to produce effervescence. The gas evolved extinguishes a burning candle. Write a balanced chemical equation for the reaction if one of the compounds formed is calcium chloride.

Ans

The metal compound A is calcium carbonate and the gas evolved is carbon dioxide (CO2). So, balanced chemical equation for this reaction is: CaCO3 (s) + 2HCl (aq) → CaCl2 (aq) + CO2 (g) + H2O (l) In this reaction, solid calcium carbonate reacts with aqueous hydrochloric acid to produce aqueous calcium chloride, carbon dioxide gas and water. The carbon dioxide gas evolved extinguishes a burning candle when it displaces the oxygen, as carbon dioxide does not support combustion.

 

Q4

Why do HCl, HNO3, etc., show acidic characters in aqueous solutions while solutions of compounds like alcohol and glucose do not show acidic character?

Ans

The presence of hydrogen ions (H+) in water determines whether a compound is acidic or not. Acids release H+ ions when they dissolve in water, making the solution acidic, as seen with HCl and HNO3. In other side, compounds like glucose and alcohol do contain hydrogen, but they don't exhibit an acidic character. This is because the hydrogen in these compounds does not separate into hydrogen ions when dissolved in water.

 

Q5	Why does an aqueous solution of an acid conduct electricity?
Ans	An aqueous solution of an acid conducts electricity because it contains charged hydrogen ions (H+) released when the acid dissolves in water. These ions allow the solution to carry an electric current.

 

Q6	Why does dry HCl gas not change the colour of the dry litmus paper?
Ans	Dry HCl gas doesn't change the color of dry litmus paper because Litmus paper responds to the concentration of hydrogen ions (H+) in an aqueous solution but Dry HCl gas doesn’t give out Hydrogen ions.

 

Q7	While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid?
Ans	When diluting an acid, it's recommended that the acid should be added to water because this minimizes the risk of violent splattering and heat release, which can occur when adding water to concentrated acid.

 

Q8	How is the concentration of hydronium ions (H3O+) affected when a solution of an acid is diluted?
Ans	When you add acid to water, there's a constant amount of hydronium ions in the fixed volume of the solution. If you dilute the solution, the hydronium ions per unit volume decrease, which lowers the hydronium ion concentration in the solution. So, we can say, Diluting an acid reduces the concentration of hydronium ions (H3O+), making the solution less acidic.

 

Q9	How is the concentration of hydroxide ions (OH–) affected when excess base is dissolved in a solution of sodium hydroxide?
Ans	When excess base is dissolved in a solution of sodium hydroxide (NaOH), the concentration of hydroxide ions (OH—) increases. Sodium hydroxide is a strong base that dissociates completely in water to release hydroxide ions. By adding more of this strong base to the solution, we are increasing the number of hydroxide ions in the solution, thus raising the concentration of OH— ions.

 

Q10

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 ion concentration? Which of this is acidic and which one is basic?

Ans

The pH scale is a logarithmic scale that measures the concentration of hydrogen ions (H+) in a solution. Lower pH values indicate higher hydrogen ion concentrations, while higher pH values indicate lower hydrogen ion concentrations. In your case: Solution A has a pH of 6, which means it has a higher hydrogen ion concentration compared to solution B. Solution A is acidic because a pH of 6 is below the neutral pH of 7. Solution B is basic because a pH of 8 is above the neutral pH of 7. So, solution A has a higher hydrogen ion concentration and is acidic, while solution B has a lower hydrogen ion concentration and is basic.

 

Q11	What effect does the concentration of H+(aq) ions have on the nature of the solution?
Ans	The nature of a solution is determined by its hydrogen ion concentration. When hydrogen ion (H+) increased solution become acidic and if hydrogen ion (H+) decreases solution become basic. If hydrogen ions (H+) and OH— ions present in equal quantity solution is neutral.

 

Q12	Do basic solutions also have H+(aq) ions? If yes, then why are these basic?
Ans	Yes, Basic solutions do contain hydrogen ions (H+(aq)), but they also have a higher concentration of hydroxide ions (OH—(aq). The predominance of OH— ions give them their basic character, as indicated by a pH greater than 7.

 

Q13	Under what soil condition do you think a farmer would treat the soil of his fields with quick lime (calcium oxide) or slaked lime (calcium hydroxide) or chalk (calcium carbonate)?
Ans	Farmers use quick lime, slaked lime, or chalk to treat acidic soils which below ph level 7 and raise their pH levels, making the soil less acidic and more suitable for crop growth.

 

Q14	What is the common name of the compound CaOCl2?
Ans	The common name of the compound CaOCl2 is "bleaching powder".

 

Q15	Name the substance which on treatment with chlorine yields bleaching powder.
Ans	The substance that, when treated with chlorine, yields bleaching powder (calcium hypochlorite, CaOCl2) is calcium hydroxide (Ca(OH)2). The reaction is as follows: Ca(OH)2 + Cl2 → CaOCl2 + H2O When chlorine gas is passed through a slaked lime (calcium hydroxide) solution, it forms bleaching powder, which is commonly used for various applications, including bleaching and disinfection.

 

Q16	Name the sodium compound which is used for softening hard water.
Ans	Sodium carbonate (Na2CO3), commonly known as soda ash or washing soda, is a sodium compound often used for softening hard water.

 

Q17	What will happen if a solution of sodium hydrocarbonate is heated? Give the equation of the reaction involved.
Ans	When a solution of sodium hydrogencarbonate (sodium bicarbonate, NaHCO3) is heated, It decompose into sodium carbonate (Na2CO3), water vapor (H2O) and carbon dioxide gas (CO2).

 

Q18	Write an equation to show the reaction between Plaster of Paris and water.
Ans	The reaction between Plaster of Paris and water is: CaSO4.½H2O +1½H2O → CaSO4.2H2O