Class 10 Chemistry Worksheet on Chapter 2 Acids, Bases and Salts ... - Free Printable
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Step-by-step solution for: Class 10 Chemistry Worksheet on Chapter 2 Acids, Bases and Salts ...
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Step-by-step solution for: Class 10 Chemistry Worksheet on Chapter 2 Acids, Bases and Salts ...
The image contains a series of chemistry-related questions. Below, I will solve and explain the solutions for each question in detail.
---
Solution:
Blue vitriol is the common name for copper(II) sulfate pentahydrate. Its chemical formula is:
\[
\boxed{\text{CuSO}_4 \cdot 5\text{H}_2\text{O}}
\]
---
Solution:
Hydrochloric acid (HCl) plays several important roles in the stomach:
1. Digestion: It helps in the digestion of proteins by activating pepsin, an enzyme that breaks down proteins into smaller peptides.
2. Sterilization: It kills bacteria and other microorganisms that may enter the stomach with food, preventing infections.
3. Absorption: It aids in the absorption of certain nutrients, such as iron and calcium.
4. pH Regulation: It maintains the acidic environment of the stomach, which is necessary for optimal enzyme activity.
---
Solution:
Dilution involves adding water to an acid or base, which reduces its concentration. The effects are as follows:
1. Acids:
- Dilution decreases the concentration of hydrogen ions (\(\text{H}^+\)) in the solution.
- This increases the pH of the solution, making it less acidic.
- For example, concentrated hydrochloric acid (\(\text{HCl}\)) has a very low pH, but when diluted, its pH increases toward 7.
2. Bases:
- Dilution decreases the concentration of hydroxide ions (\(\text{OH}^-\)) in the solution.
- This increases the pH of the solution, making it less basic.
- For example, concentrated sodium hydroxide (\(\text{NaOH}\)) has a very high pH, but when diluted, its pH decreases toward 7.
In summary, dilution makes both acids and bases weaker and moves their pH closer to 7 (neutral).
---
Solution:
Bases, especially strong bases like sodium hydroxide (\(\text{NaOH}\)) or potassium hydroxide (\(\text{KOH}\)), can react with many metals, particularly those above hydrogen in the reactivity series (e.g., aluminum, magnesium). This reaction produces hydrogen gas and corresponding metal hydroxides. For example:
\[
\text{Al} + \text{NaOH} \rightarrow \text{NaAlO}_2 + \text{H}_2 \uparrow
\]
This reaction can lead to:
1. Corrosion of the container: The metal container is gradually destroyed.
2. Release of flammable gas: Hydrogen gas produced is highly flammable and can pose a safety hazard.
Thus, bases are typically stored in non-reactive containers like plastic or glass to prevent such reactions.
---
#### i. As an antacid
#### ii. As a constituent of baking powder
Solution:
1. As an antacid:
- Baking soda (\(\text{NaHCO}_3\)) acts as an antacid because it is a weak base that neutralizes excess stomach acid (\(\text{HCl}\)).
- Chemical reaction:
\[
\text{NaHCO}_3 + \text{HCl} \rightarrow \text{NaCl} + \text{H}_2\text{O} + \text{CO}_2 \uparrow
\]
- This reaction reduces acidity in the stomach, providing relief from heartburn or indigestion.
2. As a constituent of baking powder:
- Baking soda reacts with an acid (e.g., cream of tartar or citric acid) in the presence of moisture to produce carbon dioxide gas.
- Chemical reaction:
\[
\text{NaHCO}_3 + \text{H}^+ \rightarrow \text{Na}^+ + \text{H}_2\text{O} + \text{CO}_2 \uparrow
\]
- The \(\text{CO}_2\) gas causes baked goods to rise, giving them a light and porous texture.
---
Solution:
Water of crystallization refers to the fixed number of water molecules that are chemically bound within the crystal structure of a hydrated salt. For example:
- Copper(II) sulfate pentahydrate (\(\text{CuSO}_4 \cdot 5\text{H}_2\text{O}\)) contains 5 molecules of water per formula unit.
- When this compound is heated, the water of crystallization is driven off, leaving anhydrous copper(II) sulfate (\(\text{CuSO}_4\)).
---
Solution:
Olfactory indicators are substances that change their odor when the pH of a solution changes. They are used to detect changes in acidity or basicity without visual color changes. For example:
- Phenylacetic acid has a fruity odor at neutral pH but smells like vinegar in acidic conditions.
- These indicators are useful in situations where visual observation is difficult or impractical.
---
Solution:
When diluting an acid, it is crucial to add the acid to water rather than the reverse for the following reasons:
1. Exothermic Reaction: Diluting an acid releases a significant amount of heat. If water is added to concentrated acid, the sudden release of heat can cause the mixture to splash or boil, leading to accidents.
2. Safety: Adding acid to water distributes the heat more evenly, reducing the risk of splashing or violent reactions.
3. Controlled Mixing: Adding acid slowly to water allows for better control over the reaction and ensures a safer process.
---
Solution:
Sodium chloride (table salt) can be obtained from seawater through the following steps:
1. Evaporation: Seawater is collected in large shallow ponds called salt pans.
2. Sun and Wind: The sun's heat and wind evaporate the water, leaving behind salt crystals.
3. Harvesting: The salt crystals are harvested and purified to remove impurities.
4. Refining: The crude salt is further refined to produce pure sodium chloride suitable for consumption.
---
#### a) What happens when zinc granules are heated with sodium hydroxide solution?
#### b) What does pH stand for? What does it indicate?
Solution:
#### a) Zinc granules with sodium hydroxide solution:
- Zinc reacts with sodium hydroxide and water to form sodium zincate and hydrogen gas.
- Chemical reaction:
\[
\text{Zn} + 2\text{NaOH} + 2\text{H}_2\text{O} \rightarrow \text{Na}_2[\text{Zn}(\text{OH})_4] + \text{H}_2 \uparrow
\]
- Observations: A colorless solution forms, and bubbles of hydrogen gas are released.
#### b) pH:
- Definition: pH stands for "power of hydrogen" and is a measure of the acidity or basicity of a solution.
- Indication:
- pH ranges from 0 to 14.
- pH < 7 indicates an acidic solution.
- pH = 7 indicates a neutral solution.
- pH > 7 indicates a basic (alkaline) solution.
- It is calculated as:
\[
\text{pH} = -\log[\text{H}^+]
\]
where \([\text{H}^+]\) is the hydrogen ion concentration.
---
#### a) What is gypsum? What happens when gypsum is heated at \(100^\circ \text{C}\)?
#### b) What is the common name of the compound \(\text{CaOCl}_2\)?
#### c) Explain why chlorine is used for sterilising the drinking water supply?
Solution:
#### a) Gypsum:
- Definition: Gypsum is a naturally occurring mineral with the chemical formula \(\text{CaSO}_4 \cdot 2\text{H}_2\text{O}\) (calcium sulfate dihydrate).
- Heating at \(100^\circ \text{C}\): When gypsum is heated to \(100^\circ \text{C}\), it loses part of its water of crystallization, forming hemihydrate (plaster of Paris):
\[
\text{CaSO}_4 \cdot 2\text{H}_2\text{O} \xrightarrow{100^\circ \text{C}} \text{CaSO}_4 \cdot \frac{1}{2}\text{H}_2\text{O} + \frac{3}{2}\text{H}_2\text{O}
\]
#### b) Compound \(\text{CaOCl}_2\):
- The common name of \(\text{CaOCl}_2\) is bleaching powder or calcium hypochlorite.
#### c) Chlorine for sterilizing drinking water:
- Chlorine is used to kill bacteria, viruses, and other microorganisms in drinking water.
- It works by reacting with water to form hypochlorous acid (\(\text{HOCl}\)), which is a strong oxidizing agent:
\[
\text{Cl}_2 + \text{H}_2\text{O} \rightarrow \text{HCl} + \text{HOCl}
\]
- Hypochlorous acid destroys the cell membranes and enzymes of microorganisms, rendering them harmless.
- Chlorination ensures safe and disease-free drinking water.
---
#### a) What is baking powder? How does it make the cake soft and spongy?
#### b) In addition to sodium hydrogen carbonate, baking powder contains a substance X. Name the substance X. What is the role of substance X in the baking powder?
#### c) State the two uses of sodium hydroxide.
Solution:
#### a) Baking powder:
- Definition: Baking powder is a leavening agent used in baking. It typically consists of sodium bicarbonate (\(\text{NaHCO}_3\)) and an acid (e.g., cream of tartar or monocalcium phosphate).
- How it works: When baking powder is mixed with water and heated, the sodium bicarbonate reacts with the acid to produce carbon dioxide gas:
\[
\text{NaHCO}_3 + \text{H}^+ \rightarrow \text{Na}^+ + \text{H}_2\text{O} + \text{CO}_2 \uparrow
\]
The \(\text{CO}_2\) gas creates air pockets in the batter, making the cake soft and spongy.
#### b) Substance X in baking powder:
- Substance X: The acid component, such as cream of tartar (\(\text{KHC}_4\text{H}_4\text{O}_6\)) or monocalcium phosphate (\(\text{Ca(H}_2\text{PO}_4\)_2\)).
- Role of X: It reacts with sodium bicarbonate to produce carbon dioxide gas, ensuring the leavening action occurs only when the mixture is moistened and heated.
#### c) Uses of sodium hydroxide (\(\text{NaOH}\)):
1. Cleaning Agent: It is used in drain cleaners and oven cleaners due to its ability to dissolve fats and oils.
2. Industrial Applications: It is used in the production of paper, soaps, and detergents.
3. pH Adjustment: It is used to raise the pH of solutions in various industrial and laboratory processes.
---
#### a) A knife, which is used to cut fruit, was immediately dipped into water containing drops of blue litmus solution. If the colour of the solution is changed to red, what inference can be drawn about the nature of the fruit and why?
#### b) What should be done if someone accidentally touches the leaves of a nettle plant in the wild?
#### c) Two solutions X and Y have pH = 4 and pH = 8, respectively. Which solution will give an alkaline reaction and which acidic?
Solution:
#### a) Blue litmus turning red:
- Inference: The fruit is acidic.
- Reason: Blue litmus turns red in the presence of acids. Since the litmus solution turned red after coming into contact with the knife, it indicates that the fruit released acidic juices onto the knife.
#### b) Touching nettle leaves:
- Nettle leaves contain formic acid, which causes irritation upon contact.
- Action to take:
1. Wash the affected area with soap and water to remove any remaining irritants.
2. Apply a soothing agent like calamine lotion or a paste of baking soda and water to reduce itching and inflammation.
#### c) pH values:
- Solution X (pH = 4): Acidic (since pH < 7).
- Solution Y (pH = 8): Alkaline (since pH > 7).
---
\[
\boxed{
\begin{aligned}
&\text{Q7: } \text{CuSO}_4 \cdot 5\text{H}_2\text{O} \\
&\text{Q8: } \text{Digestion, sterilization, pH regulation, nutrient absorption} \\
&\text{Q9: } \text{Dilution reduces acidity/basicity and moves pH toward 7} \\
&\text{Q10: } \text{Bases react with metals, causing corrosion and gas release} \\
&\text{Q11: } \text{Antacid: Neutralizes acid; Baking powder: Produces CO}_2 \\
&\text{Q12: } \text{Fixed water molecules in crystal structure} \\
&\text{Q13: } \text{Substances that change odor with pH} \\
&\text{Q14: } \text{Prevents splashing and ensures controlled mixing} \\
&\text{Q15: } \text{Evaporation of seawater in salt pans} \\
&\text{Q16: } \text{a) Forms Na}_2[\text{Zn(OH)}_4] \text{ and H}_2; \text{ b) pH measures acidity/basicity} \\
&\text{Q17: } \text{a) Gypsum loses water; b) Bleaching powder; c) Kills microorganisms} \\
&\text{Q18: } \text{a) Leavening agent; b) Acid (e.g., cream of tartar); c) Cleaning and pH adjustment} \\
&\text{Q19: } \text{a) Fruit is acidic; b) Wash and apply soothing agent; c) X: Acidic, Y: Alkaline}
\end{aligned}
}
\]
---
Q7. What is the chemical formula of blue vitriol?
Solution:
Blue vitriol is the common name for copper(II) sulfate pentahydrate. Its chemical formula is:
\[
\boxed{\text{CuSO}_4 \cdot 5\text{H}_2\text{O}}
\]
---
Q8. What is the role of HCl present in the stomach?
Solution:
Hydrochloric acid (HCl) plays several important roles in the stomach:
1. Digestion: It helps in the digestion of proteins by activating pepsin, an enzyme that breaks down proteins into smaller peptides.
2. Sterilization: It kills bacteria and other microorganisms that may enter the stomach with food, preventing infections.
3. Absorption: It aids in the absorption of certain nutrients, such as iron and calcium.
4. pH Regulation: It maintains the acidic environment of the stomach, which is necessary for optimal enzyme activity.
---
Q9. What is the effect of dilution on an acid or base?
Solution:
Dilution involves adding water to an acid or base, which reduces its concentration. The effects are as follows:
1. Acids:
- Dilution decreases the concentration of hydrogen ions (\(\text{H}^+\)) in the solution.
- This increases the pH of the solution, making it less acidic.
- For example, concentrated hydrochloric acid (\(\text{HCl}\)) has a very low pH, but when diluted, its pH increases toward 7.
2. Bases:
- Dilution decreases the concentration of hydroxide ions (\(\text{OH}^-\)) in the solution.
- This increases the pH of the solution, making it less basic.
- For example, concentrated sodium hydroxide (\(\text{NaOH}\)) has a very high pH, but when diluted, its pH decreases toward 7.
In summary, dilution makes both acids and bases weaker and moves their pH closer to 7 (neutral).
---
Q10. Explain why bases are not kept in metal containers?
Solution:
Bases, especially strong bases like sodium hydroxide (\(\text{NaOH}\)) or potassium hydroxide (\(\text{KOH}\)), can react with many metals, particularly those above hydrogen in the reactivity series (e.g., aluminum, magnesium). This reaction produces hydrogen gas and corresponding metal hydroxides. For example:
\[
\text{Al} + \text{NaOH} \rightarrow \text{NaAlO}_2 + \text{H}_2 \uparrow
\]
This reaction can lead to:
1. Corrosion of the container: The metal container is gradually destroyed.
2. Release of flammable gas: Hydrogen gas produced is highly flammable and can pose a safety hazard.
Thus, bases are typically stored in non-reactive containers like plastic or glass to prevent such reactions.
---
Q11. State the chemical property in each case on which the following uses of baking soda are based:
#### i. As an antacid
#### ii. As a constituent of baking powder
Solution:
1. As an antacid:
- Baking soda (\(\text{NaHCO}_3\)) acts as an antacid because it is a weak base that neutralizes excess stomach acid (\(\text{HCl}\)).
- Chemical reaction:
\[
\text{NaHCO}_3 + \text{HCl} \rightarrow \text{NaCl} + \text{H}_2\text{O} + \text{CO}_2 \uparrow
\]
- This reaction reduces acidity in the stomach, providing relief from heartburn or indigestion.
2. As a constituent of baking powder:
- Baking soda reacts with an acid (e.g., cream of tartar or citric acid) in the presence of moisture to produce carbon dioxide gas.
- Chemical reaction:
\[
\text{NaHCO}_3 + \text{H}^+ \rightarrow \text{Na}^+ + \text{H}_2\text{O} + \text{CO}_2 \uparrow
\]
- The \(\text{CO}_2\) gas causes baked goods to rise, giving them a light and porous texture.
---
Q12. What is the water of crystallisation?
Solution:
Water of crystallization refers to the fixed number of water molecules that are chemically bound within the crystal structure of a hydrated salt. For example:
- Copper(II) sulfate pentahydrate (\(\text{CuSO}_4 \cdot 5\text{H}_2\text{O}\)) contains 5 molecules of water per formula unit.
- When this compound is heated, the water of crystallization is driven off, leaving anhydrous copper(II) sulfate (\(\text{CuSO}_4\)).
---
Q13. Define olfactory indicators.
Solution:
Olfactory indicators are substances that change their odor when the pH of a solution changes. They are used to detect changes in acidity or basicity without visual color changes. For example:
- Phenylacetic acid has a fruity odor at neutral pH but smells like vinegar in acidic conditions.
- These indicators are useful in situations where visual observation is difficult or impractical.
---
Q14. While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid?
Solution:
When diluting an acid, it is crucial to add the acid to water rather than the reverse for the following reasons:
1. Exothermic Reaction: Diluting an acid releases a significant amount of heat. If water is added to concentrated acid, the sudden release of heat can cause the mixture to splash or boil, leading to accidents.
2. Safety: Adding acid to water distributes the heat more evenly, reducing the risk of splashing or violent reactions.
3. Controlled Mixing: Adding acid slowly to water allows for better control over the reaction and ensures a safer process.
---
Q15. Sea water contains many salts dissolved in it. How can the salt that we use in food (sodium chloride) be obtained?
Solution:
Sodium chloride (table salt) can be obtained from seawater through the following steps:
1. Evaporation: Seawater is collected in large shallow ponds called salt pans.
2. Sun and Wind: The sun's heat and wind evaporate the water, leaving behind salt crystals.
3. Harvesting: The salt crystals are harvested and purified to remove impurities.
4. Refining: The crude salt is further refined to produce pure sodium chloride suitable for consumption.
---
Q16.
#### a) What happens when zinc granules are heated with sodium hydroxide solution?
#### b) What does pH stand for? What does it indicate?
Solution:
#### a) Zinc granules with sodium hydroxide solution:
- Zinc reacts with sodium hydroxide and water to form sodium zincate and hydrogen gas.
- Chemical reaction:
\[
\text{Zn} + 2\text{NaOH} + 2\text{H}_2\text{O} \rightarrow \text{Na}_2[\text{Zn}(\text{OH})_4] + \text{H}_2 \uparrow
\]
- Observations: A colorless solution forms, and bubbles of hydrogen gas are released.
#### b) pH:
- Definition: pH stands for "power of hydrogen" and is a measure of the acidity or basicity of a solution.
- Indication:
- pH ranges from 0 to 14.
- pH < 7 indicates an acidic solution.
- pH = 7 indicates a neutral solution.
- pH > 7 indicates a basic (alkaline) solution.
- It is calculated as:
\[
\text{pH} = -\log[\text{H}^+]
\]
where \([\text{H}^+]\) is the hydrogen ion concentration.
---
Q17.
#### a) What is gypsum? What happens when gypsum is heated at \(100^\circ \text{C}\)?
#### b) What is the common name of the compound \(\text{CaOCl}_2\)?
#### c) Explain why chlorine is used for sterilising the drinking water supply?
Solution:
#### a) Gypsum:
- Definition: Gypsum is a naturally occurring mineral with the chemical formula \(\text{CaSO}_4 \cdot 2\text{H}_2\text{O}\) (calcium sulfate dihydrate).
- Heating at \(100^\circ \text{C}\): When gypsum is heated to \(100^\circ \text{C}\), it loses part of its water of crystallization, forming hemihydrate (plaster of Paris):
\[
\text{CaSO}_4 \cdot 2\text{H}_2\text{O} \xrightarrow{100^\circ \text{C}} \text{CaSO}_4 \cdot \frac{1}{2}\text{H}_2\text{O} + \frac{3}{2}\text{H}_2\text{O}
\]
#### b) Compound \(\text{CaOCl}_2\):
- The common name of \(\text{CaOCl}_2\) is bleaching powder or calcium hypochlorite.
#### c) Chlorine for sterilizing drinking water:
- Chlorine is used to kill bacteria, viruses, and other microorganisms in drinking water.
- It works by reacting with water to form hypochlorous acid (\(\text{HOCl}\)), which is a strong oxidizing agent:
\[
\text{Cl}_2 + \text{H}_2\text{O} \rightarrow \text{HCl} + \text{HOCl}
\]
- Hypochlorous acid destroys the cell membranes and enzymes of microorganisms, rendering them harmless.
- Chlorination ensures safe and disease-free drinking water.
---
Q18.
#### a) What is baking powder? How does it make the cake soft and spongy?
#### b) In addition to sodium hydrogen carbonate, baking powder contains a substance X. Name the substance X. What is the role of substance X in the baking powder?
#### c) State the two uses of sodium hydroxide.
Solution:
#### a) Baking powder:
- Definition: Baking powder is a leavening agent used in baking. It typically consists of sodium bicarbonate (\(\text{NaHCO}_3\)) and an acid (e.g., cream of tartar or monocalcium phosphate).
- How it works: When baking powder is mixed with water and heated, the sodium bicarbonate reacts with the acid to produce carbon dioxide gas:
\[
\text{NaHCO}_3 + \text{H}^+ \rightarrow \text{Na}^+ + \text{H}_2\text{O} + \text{CO}_2 \uparrow
\]
The \(\text{CO}_2\) gas creates air pockets in the batter, making the cake soft and spongy.
#### b) Substance X in baking powder:
- Substance X: The acid component, such as cream of tartar (\(\text{KHC}_4\text{H}_4\text{O}_6\)) or monocalcium phosphate (\(\text{Ca(H}_2\text{PO}_4\)_2\)).
- Role of X: It reacts with sodium bicarbonate to produce carbon dioxide gas, ensuring the leavening action occurs only when the mixture is moistened and heated.
#### c) Uses of sodium hydroxide (\(\text{NaOH}\)):
1. Cleaning Agent: It is used in drain cleaners and oven cleaners due to its ability to dissolve fats and oils.
2. Industrial Applications: It is used in the production of paper, soaps, and detergents.
3. pH Adjustment: It is used to raise the pH of solutions in various industrial and laboratory processes.
---
Q19.
#### a) A knife, which is used to cut fruit, was immediately dipped into water containing drops of blue litmus solution. If the colour of the solution is changed to red, what inference can be drawn about the nature of the fruit and why?
#### b) What should be done if someone accidentally touches the leaves of a nettle plant in the wild?
#### c) Two solutions X and Y have pH = 4 and pH = 8, respectively. Which solution will give an alkaline reaction and which acidic?
Solution:
#### a) Blue litmus turning red:
- Inference: The fruit is acidic.
- Reason: Blue litmus turns red in the presence of acids. Since the litmus solution turned red after coming into contact with the knife, it indicates that the fruit released acidic juices onto the knife.
#### b) Touching nettle leaves:
- Nettle leaves contain formic acid, which causes irritation upon contact.
- Action to take:
1. Wash the affected area with soap and water to remove any remaining irritants.
2. Apply a soothing agent like calamine lotion or a paste of baking soda and water to reduce itching and inflammation.
#### c) pH values:
- Solution X (pH = 4): Acidic (since pH < 7).
- Solution Y (pH = 8): Alkaline (since pH > 7).
---
Final Answer Summary:
\[
\boxed{
\begin{aligned}
&\text{Q7: } \text{CuSO}_4 \cdot 5\text{H}_2\text{O} \\
&\text{Q8: } \text{Digestion, sterilization, pH regulation, nutrient absorption} \\
&\text{Q9: } \text{Dilution reduces acidity/basicity and moves pH toward 7} \\
&\text{Q10: } \text{Bases react with metals, causing corrosion and gas release} \\
&\text{Q11: } \text{Antacid: Neutralizes acid; Baking powder: Produces CO}_2 \\
&\text{Q12: } \text{Fixed water molecules in crystal structure} \\
&\text{Q13: } \text{Substances that change odor with pH} \\
&\text{Q14: } \text{Prevents splashing and ensures controlled mixing} \\
&\text{Q15: } \text{Evaporation of seawater in salt pans} \\
&\text{Q16: } \text{a) Forms Na}_2[\text{Zn(OH)}_4] \text{ and H}_2; \text{ b) pH measures acidity/basicity} \\
&\text{Q17: } \text{a) Gypsum loses water; b) Bleaching powder; c) Kills microorganisms} \\
&\text{Q18: } \text{a) Leavening agent; b) Acid (e.g., cream of tartar); c) Cleaning and pH adjustment} \\
&\text{Q19: } \text{a) Fruit is acidic; b) Wash and apply soothing agent; c) X: Acidic, Y: Alkaline}
\end{aligned}
}
\]
Parent Tip: Review the logic above to help your child master the concept of acids bases and salts worksheet.
