Class 7th Chapter 5 Acids, Bases and Salts All textual questions with Answers for JKBOSE, Ncert Book Solution.

Exercises

(I) Fill in the blank spaces by choosing the correct words from the list given below:

(Acids, Bases and Salts Exercise Questions with answers)

List: bitter, ants, corrosive, citric, soapy, slaked lime

The acid found in lemons is citric acid.
The bases have a bitter taste and soapy touch.
The sting of the ants contains formic acid.
Sulphuric acid is highly corrosive acid.
Acidic soils are neutralized with slaked lime.

(II) Statements given below are incorrect. Write the correct statements. (Acids, Bases and Salts)

Incorrect Statement: Sulphuric acid is an example of an organic acid.

Correct Statement: Sulphuric acid is an example of an inorganic acid.

Incorrect Statement: Blue litmus paper turns red in a basic solution.

Correct Statement: Blue litmus paper turns red in an acidic solution.

Incorrect Statement: China rose solution turns green in citric acid solution.

Correct Statement: China rose solution turns pink in citric acid solution.

Incorrect Statement: Formic acid is found in the sting of a grasshopper.

Correct Statement: Formic acid is found in the sting of ants.

Incorrect Statement: During neutralization, an acid reacts with a salt to form water and base as products.

Correct Statement: During neutralization, an acid reacts with a base to form salt and water.

III) Write true or false in front of the following statements:

Tooth decay is caused by the presence of basic substance in mouth.

False: Tooth decay is primarily caused by acids produced by bacteria in the mouth, not by basic substances.

The substance which shows different colors in acids and bases are called indicators.

True: Indicators are substances that change color depending on whether they are in an acidic or basic solution, making them useful for determining the pH of a solution.

Milk of magnesia and slaked lime are examples of neutral substances.

True: Milk of magnesia and slaked lime are examples of substances that are close to neutral on the pH scale, meaning they have a pH close to 7.

Acid rain is caused by the excess of carbon dioxide in the air.

False: Acid rain is caused primarily by sulfur dioxide (SO₂) and nitrogen oxides (NOₓ) reacting with water vapor in the atmosphere to form sulfuric acid (H₂SO₄) and nitric acid (HNO₃).

Potassium hydroxide turns blue litmus red.

False: Potassium hydroxide is a strong base, so it turns red litmus paper blue, indicating its alkaline nature.

Most of the fruits contain organic acids.

True: Many fruits contain organic acids such as citric acid, tartaric acid, and malic acid, which contribute to their sour taste.

Answer the following questions from Acids, Bases, and Salts:

Question 1: Name three organic acids and three inorganic acids.

Answer:

Organic Acids:
- Citric acid (found in citrus fruits)
- Tartaric acid (found in grapes)
- Acetic acid (found in vinegar)
Inorganic Acids:
- Hydrochloric acid (found in gastric acid)
- Sulfuric acid (industrial acid used in batteries)
- Nitric acid (used in fertilizer production)

Question 2: What are indicators? Name any three indicators and state the color change which takes place in (i) acids (ii) bases.

Indicators are substances that change color in response to changes in pH, making them useful for determining whether a solution is acidic, basic, or neutral.

Examples of Indicators:

Litmus: Turns red in acids and blue in bases.
Phenolphthalein: Colorless in acids and pink in bases.
Methyl orange: Red in acids and yellow in bases.

Question 3: What are neutral substances? Give examples of two neutral substances.

Neutral substances have a pH close to 7, indicating neither acidic nor basic properties.

Examples: Water and Table salt (sodium chloride)

Question 4: How would you distinguish between acidic, basic, and neutral solutions using China rose as an indicator?

Procedure: Add a few drops of China rose solution to each solution.

Observation:

The solution that turns pink indicates it is acidic.

The solution that turns green indicates it is basic.

The solution that remains colorless indicates it is neutral.

Question 5: What do you understand by the term neutralization? Describe an activity in which neutralization of hydrochloric acid takes place with sodium hydroxide, using phenolphthalein as an indicator.

Answer: Neutralization is a chemical reaction between an acid and a base, resulting in the formation of water and salt.

Example Activity: Mix hydrochloric acid (HCl) and sodium hydroxide (NaOH) in a beaker.

Use phenolphthalein as an indicator (colorless in acids, pink in bases). Initially, the colorless HCl solution turns pink as NaOH (a base) is added until the solution becomes completely pink, indicating neutralization.

Give a reason Why:

Question 1: Why do farmers add slaked lime to acidic soils?

Answer: Farmers add slaked lime, or calcium hydroxide, to acidic soils to neutralize the acidity. This process, called liming, helps to raise the soil pH, making it less acidic and more suitable for plant growth.

Acidic soils hinder nutrient uptake by plants and affect their health, so liming improves soil fertility.

Question 2: Why is soap solution or baking soda paste applied on the part of the body stung by a bee?

Answer: Soap solution or baking soda paste is applied to bee stings because they are alkaline and help neutralize the acidic venom injected by the bee.

The venom is acidic and causes pain and inflammation. Applying an alkaline solution helps to counteract the acidity, providing relief from pain and reducing inflammation.

Question 3: Why are factory waste and city sewerage neutralized before discharging into rivers?

Answer: Factory waste and city sewerage often contain acidic or basic components that can harm aquatic life and ecosystems in rivers. Neutralization before discharge helps to adjust the pH of the waste to a level closer to neutral, reducing its harmful impact on the environment. This process minimizes water pollution and protects aquatic organisms.

Question 4: Why are antacids used for relieving stomach acidity?

Reason: Antacids are used to neutralize excess stomach acid, which can cause discomfort, heartburn, and indigestion. Antacids contain alkaline compounds like magnesium hydroxide or calcium carbonate. When taken, they react with the hydrochloric acid in the stomach, reducing acidity and providing relief from symptoms associated with excessive stomach acid.

Question: What are the four differences between acids and alkalis?

Features	Acids	Alkalis
Taste	Sour	Bitter
effect on Litmus paper	Turn blue litmus red.	Turn red litmus blue.
pH Level	Less Than 7	More than 7
Reactivity	React with metals to produce hydrogen gas	React to form salt and water
Examples	HCl, H₂SO₄ etc	NaOH, KOH, etc

Differences between acids and alkalis

Question 2: Write the equation when hydrochloric acid neutralizes sodium hydroxide.

Answer:

HCl+NaOH→NaCl+H₂O

Explanation:

Neutralization Reaction: Hydrochloric acid (HCl) reacts with sodium hydroxide (NaOH) to produce sodium chloride (NaCl), which is common table salt, and water (H₂O). This reaction is called neutralization because the acid and base neutralize each other, resulting in a neutral solution.

Extending Learning

Experiment 1: Baking Soda Solution as Invisible Ink

Materials Required :

Baking soda
Water
Cotton bud
White sheet of paper
Fresh beet root

Procedure:

Make a concentrated solution of baking soda by dissolving it in about 10 ml of water.
Using a cotton bud, write a message on a white sheet of paper with the baking soda solution.
Allow the paper to dry in the sun.
Cut a piece of fresh beet root and rub it over the invisible message on the paper.

Explanation:

Baking soda (sodium bicarbonate) is a base.
Beet root contains natural pigments called betalains which act as pH indicators.
When the beet root is rubbed over the paper, the area where the baking soda solution was applied will change color. This is because the basic nature of the baking soda reacts with the betalains in the beet root, causing a visible color change, thus revealing the hidden message.

Experiment 2: Testing Soil pH

Materials:

Soil sample from your garden
Water
Filter (e.g., coffee filter)
Litmus solution

Procedure:

Collect a sample of soil from your garden.
Make a suspension of the soil in water by mixing them together.
Filter the suspension to obtain a clear filtrate.
Test the filtrate with litmus solution to determine its pH.

Explanation:

Litmus solution is a pH indicator that changes color based on the acidity or basicity of a solution.
If the filtrate turns blue litmus paper red, the soil is acidic. If it turns red litmus paper blue, the soil is basic. If there is no color change, the soil is neutral.

Experiment 3: Turmeric Paper and Soap Solution

Materials:

White paper
Turmeric
Water
Soap solution
Cotton bud

Procedure:

Soak a white paper in a turmeric solution (made by dissolving turmeric powder in water).
Take out the paper and dry it in the sun.
Use a cotton bud to draw on the dried turmeric paper with soap solution.

Explanation:

Turmeric is a natural pH indicator that turns red in basic conditions.
Soap solution is basic in nature.
When you draw on the turmeric paper with soap solution, the area where the soap is applied will turn red or reddish-brown due to the reaction between the basic soap

solution and the turmeric indicator. This change in color reveals the drawing made with the soap solution on the turmeric paper.

Summary of Observations and Scientific Explanation:

Invisible Ink with Baking Soda:

Observation: The message becomes visible when rubbed with beet root.
Explanation: Baking soda, being basic, reacts with the acidic pigments in the beet root, causing a color change that reveals the message.

Testing Soil pH:

Observation: The color change of the litmus solution will indicate whether the soil filtrate is acidic, basic, or neutral.
Explanation: Litmus paper changes color based on the pH of the solution. This helps determine the pH nature of the soil.

Drawing on Turmeric Paper with Soap Solution:

Observation: The drawing made with soap solution appears red or reddish-brown on the turmeric paper.
Explanation: The soap solution is basic, and turmeric changes color in basic conditions, showing a visible change where the soap was applied.

These experiments utilize the principles of acids, bases, and pH indicators to create visual and observable changes, demonstrating fundamental chemical reactions and properties.

Certainly! Below is a structured Q&A for your blog post based on the provided image:

Understanding Acids, Bases, and Their Reactions

1. Differences Between Acids and Bases

Q: State differences between acids and bases.

Acids have a sour taste and turn blue litmus paper red. They release hydrogen ions (H⁺) in solution.
Bases have a bitter taste and turn red litmus paper blue. They release hydroxide ions (OH⁻) in solution.

2. The Nature of Ammonia

Q: Ammonia is found in many household products, such as window cleaners. It turns red litmus blue. What is its nature?

A: Ammonia is basic in nature as it turns red litmus paper blue.

3. Source and Use of Litmus Solution

Q: Name the source from which litmus solution is obtained. What is the use of this solution?

A: Litmus solution is obtained from lichens. It is used to test whether a substance is acidic or basic.

4. Nature of Distilled Water

Q: Is distilled water acidic, basic, or neutral? How would you verify it?

A: Distilled water is neutral. You can verify this by testing it with both red and blue litmus papers, which will not change color.

5. The Process of Neutralization

Q: Describe the process of neutralization with the help of an example.

A: Neutralization is the reaction between an acid and a base to form salt and water. For example, when hydrochloric acid (HCl) reacts with sodium hydroxide (NaOH), sodium chloride (salt) and water are formed:

HCl + NaOH – – – – – – – – > NaCl + H2O

6. True or False Statements

Q: Mark ‘T’ if the statement is true and ‘F’ if it is false:

(i) Nitric acid turns red litmus blue. (T/F)

A: False

(ii) Sodium hydroxide turns blue litmus red. (T/F)

A: False

(iii) Sodium hydroxide and hydrochloric acid neutralise each other and form salt and water. (T/F)

A: True

(iv) Indicator is a substance which shows different colours in acidic and basic solutions. (T/F)

A: True

(v) Tooth decay is caused by the presence of a base. (T/F)

A: False

7. Identifying Drinks

Q: Dorji has a few bottles of soft drink in his restaurant. But, unfortunately, these are not labelled. He has to serve the drinks on the demand of customers. One customer wants acidic drink, another wants basic and third one wants neutral drink. How will Dorji decide which drink is to be served to whom?

A: Dorji can use litmus paper to identify the drinks:

An acidic drink will turn blue litmus paper red.
A basic drink will turn red litmus paper blue.
A neutral drink will not change the color of either red or blue litmus paper.

8. Explanation on Antacids

Q: Explain why an antacid tablet is taken when you suffer from acidity.

A: Antacid tablets are taken to neutralize excess stomach acid. They contain bases, which react with and neutralize the hydrochloric acid in the stomach, providing relief from acidity and heartburn.

Questions and Answers on Acids, Bases, and Indicators

1. How is calamine solution used in treating ant bites?

Answer: Calamine solution neutralizes the acidic formic acid from the ant bite, providing relief from pain and itching.

2. Why is factory waste neutralized before disposal into water bodies?

Answer: Neutralization prevents environmental harm, protecting aquatic life and maintaining ecological balance.

3. How can you identify hydrochloric acid, sodium hydroxide, and sugar solution using turmeric indicator?

Answer: Turmeric turns reddish-brown with sodium hydroxide (base) and remains unchanged with hydrochloric acid (acid) and sugar solution (neutral).

4. What can be inferred if blue litmus paper remains blue after being dipped in a solution?

Answer: The solution is either neutral or basic as blue litmus paper turns red only in acidic conditions.

5. Which statements about indicators are correct?

(a) Both acids and bases change the color of all indicators.
(b) If an indicator gives a color change with an acid, it does not give a change with a base.
(c) If an indicator changes color with a base, it does not change color with an acid.
(d) Change of color in an acid and a base depends on the type of the indicator.

Answer: (iii) b, c, and d are correct.

Additional Questions and Answers

6. What are common natural indicators used to determine acidity or basicity?

Answer: Litmus, red cabbage juice, and turmeric.

7. How does red cabbage juice indicate pH levels?

Answer: It contains anthocyanin that changes color: red in acidic, purple in neutral, and green/yellow in basic solutions.

8. Why is baking soda solution used to write secret messages?

Answer: Baking soda (a base) reacts with beetroot pigments, revealing a color change that uncovers the message.

9. What are the main components of DNA related to acids?

Answer: DNA contains nucleotides made of deoxyribonucleic acid, essential for genetic information.

10. What type of acids are amino acids?

Answer: Organic compounds that are building blocks for proteins.

11. How can you test soil acidity using red cabbage juice?

Answer: Mix soil with water and add red cabbage juice; color changes will indicate the soil’s pH.

12. What is the role of fatty acids in the human body?

Answer: Essential for energy storage and cell membrane structure.

13. How does beetroot juice act as an indicator?

Answer: Changes color when reacting with acids (red) or bases (yellow/orange).

14. How does litmus paper work as an indicator?

Answer: Changes color in response to pH: blue turns red in acids, and red turns blue in bases.

15. Why is it important to test the pH of water in fish tanks?

Answer: Proper pH is crucial for the health of aquatic life.

16. What is the significance of the pH scale?

Answer: Measures the acidity or basicity of a solution from 0 (very acidic) to 14 (very basic), with 7 being neutral.

17. How can turmeric be used to test for bases?

Answer: Contains curcumin, which turns reddish-brown in the presence of bases.

18. What happens when an acid reacts with a base?

Answer: They form salt and water, a neutralization reaction.

19. How can phenolphthalein be used as an indicator?

Answer: Colorless in acids but turns pink in bases.

20. What is the purpose of using universal indicator paper?

Answer: Provides a wide range of colors for precise pH measurement.

21. How does acid rain form?

Answer: Pollutants like sulfur dioxide and nitrogen oxides react with water vapor, forming acidic compounds in rain.

22. Why is vinegar commonly used to test for bases?

Answer: Reacts with bases to produce a noticeable color change in many indicators.

23. What is the effect of pH on enzyme activity?

Answer: Enzymes have optimal pH ranges; deviations can reduce activity or denature them.

24. How does baking soda neutralize stomach acid?

Answer: Reacts with hydrochloric acid to form salt, water, and carbon dioxide.

25. How can you identify a weak acid from a strong acid using indicators?

Answer: Weak acids partially dissociate, causing less pronounced color changes compared to strong acids.

26. What role do acids play in food preservation?

Answer: Inhibit bacterial growth, preserving food by creating an environment unsuitable for spoilage.

27. Why should acidic and basic cleaning agents be handled with care?

Answer: They can cause chemical burns and damage surfaces.

28. How do acids and bases affect plant growth?

Answer: Soil pH affects nutrient availability, influencing plant growth.

29. What is the function of hydrochloric acid in the stomach?

Answer: Aids digestion and kills harmful bacteria.

30. Why do antacids relieve heartburn?

Answer: Neutralize excess stomach acid, relieving the burning sensation.

31. How do buffers work to maintain pH levels?

Answer: Neutralize added acids or bases, maintaining stable pH in systems.

32. Why are acidic beverages like soda corrosive to teeth?

Answer: Can erode tooth enamel, leading to cavities.

33. How does the pH of blood affect bodily functions?

Answer: Blood pH regulation is crucial for enzyme activity and metabolism.

34. What are the environmental impacts of acid rain?

Answer: Damages forests, aquatic ecosystems, and infrastructure.

35. How can you test the effectiveness of an antacid?

Answer: Measure pH changes in simulated stomach acid before and after antacid addition.

36. What are the benefits of using natural indicators?

Answer: Eco-friendly, readily available, and visually indicate pH without sophisticated equipment.

Extended Learning Questions and Answers

37. How do you write a secret message with baking soda and beetroot?

Answer: Use baking soda solution to write a message on paper. Once dried, rub fresh beetroot over it to reveal the message due to a color change reaction.

38. How do you prepare red cabbage juice for pH testing?

Answer: Boil red cabbage in water, strain to obtain the juice, and use it as an indicator to test solutions for acidity or basicity by observing color changes.

39. How can you test soil acidity in your area?

Answer: Mix soil with water, add red cabbage juice, and observe the color change to determine if the soil is acidic, neutral, or basic.

40. What should you ask a doctor about preventing acidity?

Answer: Inquire about medicines prescribed for acidity and preventive measures such as diet and lifestyle changes.

Did You Know Questions and Answers

41. What is the role of deoxyribonucleic acid (DNA) in the body?

Answer: DNA controls features such as appearance and height, encoding genetic information essential for cellular functions.

42. How are amino acids related to proteins?

Answer: Amino acids are the building blocks that form proteins, essential for various bodily functions.

43. What is the significance of fatty acids in the body?

Answer: Fatty acids are part of fats in the body, important for energy storage and cell membrane integrity.