CHAPTER 2 Acids Bases and Salts KSEEB SSLC CLASS 10 SCIENCE SOLUTIONS

CHAPTER 2 Acids Bases and Salts KSEEB SSLC CLASS 10 SCIENCE SOLUTIONS English medium Karnataka state board,the Answers Are Prepared By Our Teachers Which Are Simple ,Pointwise,Easy To Read And Remember

CHAPTER 2 Acids Bases and Salts KSEEB SSLC CLASS 10 SCIENCE SOLUTIONS

1.You have been provided with three test tubes. One of them contains distilled water and the other two contain an acidic solution and a basic solution, respectively. If you are given only red litmus paper, how will you identify the contents of each test tube?

Answer:-

. Observation: We have three test tubes.

. Materials Provided: Red litmus paper.

. Test Tube Contents:

One has distilled water.
The other two have acidic and basic solutions.

Procedure:

Take a piece of red litmus paper.
Dip the red litmus paper into each test tube, one at a time.

Observation:

If the litmus paper turns blue, it indicates a basic solution.
If the litmus paper remains red, it indicates either distilled water or an acidic solution.

Further Test:

To differentiate between distilled water and an acidic solution:

Take another piece of red litmus paper.
Dip it into the test tube that didn’t turn blue.
If the litmus paper remains red, it indicates distilled water.
If the litmus paper turns blue, it indicates an acidic solution.

Conclusion: By observing the color change of the red litmus paper, we can identify the contents of each test tube. Blue indicates a basic solution, while red indicates either distilled water (if it remains red) or an acidic solution (if it turns blue).

2.Why should curd and sour substances not be kept in brass and copper vessels?

Answer:-

Reason for not keeping curd and sour substances in brass and copper vessels: Cause: Brass and copper contain metal ions that react with acids.

Result: This reaction can lead to the formation of harmful compounds.

Example: Acids in curd or sour substances react with brass/copper, forming toxic compounds like copper acetate.

Effect: Consumption of such substances stored in these vessels may lead to health hazards.

2.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?

Answer:-

Gas liberated when an acid reacts with a metal:

Gas: Hydrogen gas is usually liberated.

Example: Reaction between hydrochloric acid (HCl) and zinc:

Chemical Equation: Zn+ 2HCl→ZnCl2 + H2

Testing for presence of hydrogen gas:

Procedure: Place a burning candle near the mouth of the test tube where the reaction is occurring.

Observation: Hydrogen gas being lighter than air, it rises and burns with a pop sound when it reaches the flame.

3.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

Answer:-

Reaction of metal compound A with hydrochloric acid and its products:

Reaction: Metal compound A reacts with dilute hydrochloric acid to produce effervescence.

Resulting Compound: Calcium chloride is formed as one of the compounds.

Balanced Chemical Equation:

Metal compound A + 2HCl →Gas + Calcium chloride

Testing for effervescence: Effervescence indicates the evolution of gas. To confirm the presence of hydrogen gas:

Procedure: Bring a burning candle near the mouth of the test tube.

Observation: If the gas extinguishes the burning candle, it indicates the presence of hydrogen gas.

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

Answer:-

Acids like HCl and HNO3 show acidic properties because:

They release hydrogen ions (H+) in water.
This release of hydrogen ions causes characteristic sour taste, turns blue litmus paper red, and enables conductivity of electricity.

Compounds like alcohol and glucose:

Do not release hydrogen ions when dissolved in water.
Hence, they do not exhibit acidic properties.

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

Answer:-

Aqueous solutions of acids conduct electricity because they contain hydrogen ions (H+) and negatively charged ions (anions) produced when the acid dissociates in water.
These ions can move freely in the solution, allowing the flow of electric current.

3.Why does dry HCl gas not change the color of the dry litmus paper?

Answer:-

Dry HCl gas does not change the color of dry litmus paper because it does not produce hydrogen ions (H+) in the absence of water.
Litmus paper only changes color when it comes into contact with hydrogen ions.

4.While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid?

Answer:-

It is recommended to add acid to water and not water to acid because the process of diluting acid with water is highly exothermic.
Adding water to concentrated acid can cause a rapid release of heat, potentially causing splashing and leading to burns.
Adding acid to water allows for better control of the reaction and reduces the risk of splashing.

5.How is the concentration of hydronium ions (H3O+) affected when a solution of an acid is diluted?

Answer:-

When a solution of an acid is diluted, the concentration of hydronium ions (H3O+) decreases per unit volume.
Dilution increases the volume of the solution while keeping the amount of acid constant, leading to a decrease in the concentration of hydronium ions.

6.How is the concentration of hydroxide ions (OH–) affected when excess base is dissolved in a solution of sodium hydroxide?

Answer:-

When excess base is dissolved in a solution of sodium hydroxide, the concentration of hydroxide ions (OH–) increases.
This is because the excess base dissociates to release more hydroxide ions, leading to an increase in the concentration of hydroxide ions in the solution.

1.You have two solutions, A and B. The pH of solution A is 6 and the pH of solution B is 8. Which solution has more hydrogen ion concentration? Which of these is acidic and which one is basic?

Answer:-

Solution A has a lower pH value (6), indicating higher hydrogen ion concentration compared to solution B (pH 8).
Since pH is lower than 7, solution A is acidic, while solution B is basic.

2.What effect does the concentration of H+(aq) ions have on the nature of the solution?

Answer:-

The concentration of H+(aq) ions determines the acidic or basic nature of the solution.
Higher concentration of H+(aq) ions makes the solution more acidic, while lower concentration makes it more basic.

3.Do basic solutions also have H+(aq) ions? If yes, then why are these basic?

Answer:-

Yes, basic solutions also have H+(aq) ions, but in much lower concentration compared to acidic solutions.
Basic solutions are characterized by a higher concentration of OH-(aq) ions, which make them basic despite the presence of some H+(aq) ions.

4.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)?

Answer:-

Farmers would treat acidic soils with quick lime (calcium oxide), slaked lime (calcium hydroxide), or chalk (calcium carbonate).
These substances neutralize the excess acidity in the soil, raising its pH level to a more suitable range for plant growth.

1.What are some examples of salts mentioned in the passage?

Answer:-

Potassium sulphate, sodium sulphate, calcium sulphate, magnesium sulphate, copper sulphate, sodium chloride, sodium nitrate, sodium carbonate, and ammonium chloride.

2.What determines whether a salt is acidic, basic, or neutral?

Answer:-

Salts of strong acid + strong base = neutral (pH 7)
Salts of strong acid + weak base = acidic (pH < 7)
Salts of strong base + weak acid = basic (pH > 7)

3.How can the pH of salts be determined?

Answer:-

The pH of salts can be determined by dissolving the salts in water, testing their solubility, and then using litmus paper or pH paper to measure the pH of the resulting solution.

4.What is the significance of water of crystallization in salts like copper sulphate and gypsum?

Answer:-

Water of crystallization: fixed water molecules in salt.
Example: Copper sulphate (CuSO4·5H2O), gypsum (CaSO4·2H2O).
Heating removes water, salt turns white.
Re-moistening restores color and structure, indicating water reabsorption.

1.What is the common name of the compound CaOCl2 ?

Answer:-

The common name of the compound CaOCl2 is “bleaching powder.”

2.Name the substance which on treatment with chlorine yields bleaching powder.

Answer:-

The substance that, on treatment with chlorine, yields bleaching powder is dry slaked lime or calcium hydroxide [Ca(OH)2].

3.Name the sodium compound which is used for softening hard water.

Answer:-

Sodium carbonate (Na2CO3) is the sodium compound used for softening hard water.

4.What will happen if a solution of sodium hydrocarbonate is heated? Give the equation of the reaction involved.

Answer:-

When a solution of sodium hydrogencarbonate (NaHCO3) is heated, it decomposes to form sodium carbonate (Na2CO3), water (H2O), and carbon dioxide (CO2) gas. The equation for this reaction is:

2NaHCO3(s) -> Na2CO3(s) + H2O(l) + CO2(g)

5.Write an equation to show the reaction between Plaster of Paris and water.

The reaction between Plaster of Paris (calcium sulphate hemihydrate) and water is as follows:

CaSO4.1/2H2O(s) + 1.5H2O(l) -> CaSO4.2H2O(s)

This reaction results in the formation of gypsum, which is the hydrated form of calcium sulphate.

Excercise

1.A solution turns red litmus blue, its pH is likely to be:

(a) 1

(b) 4

(d) 10

Answer:-

(d) 10

2.A solution reacts with crushed egg-shells to give a gas that turns lime-water milky. The solution contains:

(a) NaCl

(b) HCl

(d) KCl

Answer:-

(b) HCl

3..10 mL of a solution of NaOH is found to be completely neutralized by 8 mL of a given solution of HCl. If we take 20 mL of the same solution of NaOH, the amount HCl solution (the same solution as before) required to neutralize it will be:

(a) 4 mL

(b) 8 mL

(d) 16 mL

Answer:-

4.Which one of the following types of medicines is used for treating indigestion?

(a) Antibiotic

(b) Analgesic

(d) Antiseptic

Answer:-

5.Write word equations and then balanced equations for the reaction taking place when:

(a) dilute sulfuric acid reacts with zinc granules.

(b) dilute hydrochloric acid reacts with magnesium ribbon.

(d) dilute hydrochloric acid reacts with iron filings.

Answer:-

(a) Zinc + sulfuric acid → Zinc sulfate + Hydrogen gas

Zn + H2SO4 →ZnSO4 + H2

(b) Magnesium + hydrochloric acid → Magnesium chloride + Hydrogen gas

Mg + 2HCl →MgCl2 + H2

2Al + 3H2SO4 →Al2(SO4)3 + 3H2

(d) Iron + hydrochloric acid → Iron chloride + Hydrogen gas

Fe + 2HCl →FeCl2 + H2

6.Compounds such as alcohols and glucose also contain hydrogen but are not categorized as acids. Describe an Activity to prove it.

Answer:-

To prove that compounds like alcohols and glucose are not acids, we can perform the following activity:

Take litmus paper and test the pH of solutions of alcohol and glucose.
Since alcohols and glucose do not release hydrogen ions (H+) when dissolved in water, the litmus paper will not change color, indicating that the solutions are neutral.

7.Why does distilled water not conduct electricity, whereas rainwater does?

Answer:-

Distilled water does not conduct electricity because it does not contain ions. Rainwater, on the other hand, picks up ions from the atmosphere as it falls, making it conductive.

8.Why do acids not show acidic behavior in the absence of water?

Answer:-

Acids show acidic behavior only in the presence of water because the acidic behavior is a result of the release of hydrogen ions (H+) in aqueous solutions.

9.Five solutions A,B,C,D and E when tested with universal indicator showed pH as 4,1,11,7 and 9, respectively. Which solution is:

(a) neutral?

(b) strongly alkaline?

(d) weakly acidic?

(e) weakly alkaline?

Answer:-

(a) Neutral: Solution D (pH 7)

(b) Strongly alkaline: Solution C (pH 11)

(d) Weakly acidic: Solution A (pH 4)

(e) Weakly alkaline: Solution E (pH 9)

10.Equal lengths of magnesium ribbons are taken in test tubes A and B. Hydrochloric acid (HCl) is added to test tube A, while acetic acid (CH3COOH) is added to test tube B. Amount and concentration taken for both the acids are same. In which test tube will the fizzing occur more vigorously and why?

Answer:-

Fizzing will occur more vigorously in test tube A because hydrochloric acid is a stronger acid compared to acetic acid, resulting in a more vigorous reaction with magnesium.

11.Fresh milk has a pH of 6. How do you think the pH will change as it turns into curd? Explain your answer.

Answer:-

As milk turns into curd, the pH will decrease. This is because the lactic acid bacteria present in curd produce lactic acid as they ferment lactose (milk sugar), leading to a decrease in pH.

12.A milkman adds a very small amount of baking soda to fresh milk.

(a) Why does he shift the pH of the fresh milk from 6 to slightly alkaline?

(b) Why does this milk take a long time to set as curd?

Answer:-

(a) The milkman shifts the pH of fresh milk from 6 to slightly alkaline using baking soda to prevent the milk from turning sour quickly. Alkaline conditions inhibit the growth of bacteria that cause milk to spoil.

(b) The milk takes a long time to set as curd because the presence of baking soda slows down the coagulation process of milk proteins required for curd formation.

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

Answer:-

Plaster of Paris should be stored in a moisture-proof container because it readily absorbs moisture from the air, leading to its premature hardening or degradation.

14.What is a neutralization reaction? Give two examples.

Answer:-

A neutralization reaction is a chemical reaction between an acid and a base to form water and a salt. Two examples are:

HCl + NaOH →NaCl + H2O (Hydrochloric acid reacts with sodium hydroxide to form sodium chloride and water)

H2SO4 + 2NaOH →Na2SO4 + 2H2O(Sulfuric acid reacts with sodium hydroxide to form sodium sulfate and water)

15.Give two important uses of washing soda and baking soda.

Answer:-

Uses of washing soda: It is used in the manufacture of glass, soap, and paper, as a cleaning agent for domestic purposes, and for removing permanent hardness of water.
Uses of baking soda: It is used for making baking powder, as an ingredient in antacids, in soda-acid fire extinguishers, and for various household cleaning purposes.

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