CBSE Class 10 Science Acids Bases and Salts VBQs Set 06

This page collects 21 value based and real-life questions from Class 10 Science Chapter 2, Acids, Bases and Salts, with step-by-step answers and teacher's notes. They connect the chapter to first aid for stings, tooth care, soil treatment, river pollution, acid rain and the care of monuments, and show the values of safety and environmental concern.

Real Life and Value Based Questions

Question 1. Why is it wrong to treat a bee sting with vinegar? Why is it wrong to treat a wasp sting with baking soda solution?
Answer:
A bee sting injects formic acid (an acid) into the skin. Vinegar is acetic acid, so it cannot neutralise it; a mild base such as baking soda should be used.
A wasp sting injects an alkaline liquid. Baking soda is also a base and cannot neutralise it; a mild acid such as vinegar should be used.
In simple words: Acid stings need a base; basic stings need an acid.

Teacher's Note:
1. Neutralisation needs the opposite type of substance.
2. Name the correct treatment for each sting.

Question 2. Ayush along with his friend went to a nearby shopping mall. They were standing under a tree when an ant stung his friend on his hands due to which his friend's hand was paining a lot. Name the chemical that is responsible for inducing such pain in the hand of Ayush's friend. Also, write its chemical formula.
Answer:
The chemical is formic acid (methanoic acid), HCOOH.
The pain can be relieved by rubbing a mild base such as baking soda on the stung area.
In simple words: An ant sting injects formic acid, and a mild base gives relief.

Teacher's Note:
1. Value: help a friend quickly with simple first aid.
2. Neutralisation relieves the sting.

Question 3. Sabina saw that her mother was coating the raw fish with a layer of table salt (NaCl), and she got intrigued by seeing this. Her mother told her that salt is used as a preservative because it helps reduce the water content of food. Sabina's mother also told her that some other salts that are used in daily households are also prepared from common salt. As a result, Sabina tried to find some other salts that are produced by using NaCl as the raw material. Name any two salts of such kind.
Answer:
Washing soda (sodium carbonate, Na₂CO₃·10H₂O) and baking soda (sodium hydrogencarbonate, NaHCO₃). Sodium hydroxide and bleaching powder are also made from common salt.
In simple words: Common salt is the raw material for washing soda and baking soda.

Teacher's Note:
1. Name salts, not only compounds.
2. NaCl is called the raw material of the chlor-alkali industry.

Question 4. Amit saw that in his kitchen garden, the plants do not grow well. He suggested his mother to get the soil tested and it was found that the soil is acidic in nature and the pH value is between 4.0-5.0. What should be added to treat the soil and why?
Answer:
Quick lime (calcium oxide), slaked lime (calcium hydroxide) or chalk (calcium carbonate) should be added.
All of them are basic, so they neutralise the acidity of the soil and bring its pH near neutral, so plants grow well.
In simple words: Add lime to acidic soil.

Teacher's Note:
1. Value: caring for the garden and the environment.
2. Bases neutralise acids.

Question 5. A soil sample solution was analyzed with universal pH indicator paper and the colour of the paper turned yellowish.
(i) What is the nature of soil?
(ii) What type of substance should the farmer add to the soil in order to get a suitable soil for farming?
Answer:
(i) Yellow colour of universal indicator paper shows a weakly acidic pH, so the soil is acidic.
(ii) The farmer should add a base such as quick lime (calcium oxide) or slaked lime (calcium hydroxide) to neutralise the acidity.
In simple words: Acidic soil is treated with lime.

Teacher's Note:
1. Farmers also use organic manure to adjust pH.
2. Bases neutralise acidic soil.

Question 6. While constructing a house, a builder selects marble flooring and marble table tops for the kitchen where vinegar and juice of lemon, tamarind etc. are more often used for cooking. Will you agree to this selection and why?
Answer:
No, I will not agree.
Marble is calcium carbonate. It reacts with acids in vinegar and the juice of lemon or tamarind, giving carbon dioxide, so the surface is eaten away and loses its shine: CaCO₃ + 2CH₃COOH → (CH₃COO)₂Ca + H₂O + CO₂.
In simple words: Acids damage marble because it is a carbonate.

Teacher's Note:
1. Metal carbonate + acid gives salt, water and CO₂.
2. Suggest tiles or granite instead.

Question 7. Lemon is used for restoring the shine of tarnished copper vessels. Why?
Answer:
Copper vessels in moist air get a dull green coating of basic copper carbonate.
Lemon (and tamarind) contains citric acid, which reacts with and dissolves this coating, and the shiny surface of copper is restored.
In simple words: Citric acid in lemon dissolves the dull coating.

Teacher's Note:
1. Acids react with basic copper carbonate.
2. Tamarind works in the same way.

Question 8. Naman and Raghav performed an experiment in which they mixed concentrated sulphuric acid with water. Naman mixes water to acid and Raghav mixes acid to water slowly with constant stirring. Mention the suitable reason for selecting the one which you find is a correct method and discarding the one which one is wrong.
Answer:
Raghav's method is correct.
Mixing concentrated sulphuric acid and water is highly exothermic. If water is added to the acid (Naman), the heat can make the acid splash on the face or body and the glass container may break.
When acid is added to water slowly with stirring (Raghav), the heat is evenly absorbed by the large amount of water.
In simple words: Always add acid to water, never water to acid.

Teacher's Note:
1. Name the person who is correct.
2. Use the word exothermic.

Question 9. Why do we feel burning sensation in stomach when we over eat? What is the medicine used called? Give one example.
Answer:
On overeating, the stomach produces excess hydrochloric acid, which causes pain and burning sensation (acidity).
The medicine used is called an antacid. Example: milk of magnesia, Mg(OH)₂ (or sodium hydrogencarbonate).
In simple words: Excess stomach acid is cancelled by an antacid.

Teacher's Note:
1. Antacids are mild bases.
2. Give one named example.

Question 10. Why should curd and sour substances not be kept in brass and copper vessels?
Answer:
Curd and other sour substances contain acids.
These acids react with the metals of brass and copper vessels and form harmful (poisonous) compounds, which spoil the food and can cause food poisoning.
In simple words: Acids in sour food attack the metal and make the food unsafe.

Teacher's Note:
1. Say clearly that a harmful salt is formed.
2. The same reason is given for not storing pickles in metal containers.

Question 11. If someone is suffering from the problem of acidity after overeating, which of the following would you suggest as remedy? Lemon juice, Vinegar, Baking soda solution. Give reason for your choice.
Answer:
Baking soda solution should be suggested.
It is mildly basic, so it neutralises the excess hydrochloric acid in the stomach and gives relief. Lemon juice and vinegar are acidic and would increase the acidity.
In simple words: A mild base is used to cancel excess acid.

Teacher's Note:
1. Antacids such as milk of magnesia work the same way.
2. Give the reason, not just the name.

Question 12. A knife which is used to cut a fruit, was immediately dipped into water containing drops of blue litmus solution. If the colour of solution changes to red, what inference can be drawn about the nature of the fruit and why?
Answer:
The fruit is acidic (sour) in nature.
The fruit juice sticking to the knife contains an acid that gives H⁺ ions, and an acid turns blue litmus red.
In simple words: Blue litmus turning red shows an acid.

Teacher's Note:
1. Citric acid is present in citrus fruits.
2. Give the reason with the indicator behaviour.

Question 13. What do you mean by acid rain?
Answer:
When the pH of rain water is lower than 5.6 it is called acid rain. It is formed when oxides of sulphur and nitrogen dissolve in rain water.
In simple words: Acid rain has pH below 5.6.

Teacher's Note:
1. When acid rain flows into rivers it lowers the pH of the water.
2. This makes survival of aquatic life difficult.

Question 14. Explain how the pH change in the river water can endanger the lives of aquatic animal like fish.
Answer:
Acid rain has a pH less than 5.6. When it flows into rivers, it lowers the pH of the river water. Aquatic animals can survive only in a narrow range of pH, so a lower pH makes their survival difficult.
In simple words: Acidic river water harms fish.

Teacher's Note:
1. Mention acid rain and the pH value 5.6.
2. Fish and other aquatic life need a particular pH.

Case Based and Competency Questions

Question 15. There are many wonderful natural acid-base indicators. One such ubiquitous food item in Indian households is turmeric powder. The dazzling yellow colour of turmeric turns deep red when exposed to a basic/alkaline substance. However, it remains yellow if the test sample is neutral or acidic.
(A) How will you prepare turmeric indicator from turmeric powder?
(B) Give reason:
(i) Turmeric is used as a natural indicator.
(ii) Turmeric turns into brownish red with soap solution. (C)
(i) Design an activity to demonstrate change in colour in any two indicators other than turmeric.
(ii) Write your observations.
Answer:
(A) Make a paste of a tablespoon of turmeric powder, apply it on blotting or filter paper and dry it. Cut thin strips of the yellow paper obtained.
(B) (i) Turmeric changes its colour in basic medium (yellow to red) and not in acid or neutral medium, so it indicates whether a substance is basic. (ii) Soap solution is basic, so it turns yellow turmeric into brownish red.
(C)(i) Take an acidic solution in test tube A and a basic solution in test tube B. Add a few drops of blue litmus to A and red litmus to B. In fresh tubes, add a few drops of phenolphthalein to each.
(ii) Blue litmus turns red in A, and red litmus turns blue in B. Phenolphthalein stays colourless in the acid and turns pink in the base.
In simple words: Turmeric stays yellow in acids and turns red in bases.

Teacher's Note:
1. Mention colour changes with both acid and base.
2. Turmeric stains on clothes turn red with soap.

Question 16. A white shirt has a yellow stain of curry. When soap is rubbed on this shirt during washing, the yellow stain turns reddish-brown. On rinsing the shirt with plenty of water, the reddish-brown stain turns yellow again.
(i) Name the natural indicator present in curry stain.
(ii) Explain the changes in colour of this indicator which take place during washing and rinsing the shirt.
(iii) What is the nature of soap (acidic/basic) as shown by the indicator present in curry stain?
Answer:
(i) Turmeric.
(ii) Soap solution is basic, and turmeric turns reddish-brown in a base. On rinsing, the soap is washed away, so the medium is no longer basic and the stain turns yellow again.
(iii) Soap is basic in nature.
In simple words: Turmeric is yellow in neutral or acidic medium and reddish-brown in a base.

Teacher's Note:
1. Turmeric is a natural indicator.
2. Soap is a salt of a strong base and weak fatty acid, so it is basic.

Question 17. (A) Explain how tooth decay can be caused by change in pH.
(B) Which substance is known as the hardest substance in the body and where is it located?
(C) What is the best and easiest way to prevent tooth decay in day-to-day life?
Answer:
(A) Bacteria in the mouth break down sugar and food particles left after eating and form acids. When the pH of the mouth falls below 5.5, the acid corrodes the tooth enamel and tooth decay begins.
(B) Tooth enamel (calcium hydroxyapatite, a form of calcium phosphate) is the hardest substance in the body; it is the outer covering of the teeth.
(C) Clean the mouth and brush the teeth after eating, using a toothpaste, which is basic and neutralises the acid.
In simple words: Acid from food attacks enamel; basic toothpaste neutralises it.

Teacher's Note:
1. Value: good dental hygiene.
2. Quote the critical pH value 5.5.

Question 18. Madhav took 10 g of a green salt powder in a covered beaker. He heated the beaker for 15 minutes. Madhav noticed that the salt powder turned whitish after 15 minutes. He also found some droplets on the inner surface of the beaker cover. Madhav added a few drops of water to the whitish powder. The powder turned green.
(A) Write the name and formula of the green salt powder.
(B) Madhav noticed some droplets on the inner surface of the beaker cover. What are these drops? Why are the droplets seen on the inner surface of the beaker?
(C) Support by providing a suitable reason as to why the powder turned green upon addition of water droplets, and illustrate the activity performed by Madhav with the help of a chemical reaction.
Answer:
(A) Hydrated ferrous sulphate (green vitriol), FeSO₄·7H₂O.
(B) The droplets are water. On heating, the salt loses its water of crystallisation as water vapour, which condenses on the cooler inner surface of the cover.
(C) On adding water, the anhydrous ferrous sulphate takes up water of crystallisation again and regains the green colour (rehydration). FeSO₄·7H₂O → FeSO₄ + 7H₂O on heating, and FeSO₄ + 7H₂O → FeSO₄·7H₂O on adding water.
In simple words: Water of crystallisation gives the green colour, and it can be removed and restored.

Teacher's Note:
1. The colour is linked to the water of crystallisation.
2. Remember the number of water molecules: copper sulphate 5, washing soda 10, gypsum 2.

Question 19. (a) Write the chemical name and formula of marble.
(b) It has been found that marbles of Taj are getting corroded due to development of industrial areas around it. Explain this fact giving a chemical equation. (c)
(i) What happens when CO₂ is passed through lime water?
(ii) What happens when CO₂ is passed in excess through lime water?
Answer:
(a) Marble is calcium carbonate, CaCO₃.
(b) Industries around Agra release oxides of sulphur and nitrogen. These dissolve in rain water and form acid rain (sulphuric and nitric acid). The acid reacts with the marble of the Taj Mahal and corrodes it: CaCO₃ + H₂SO₄ → CaSO₄ + H₂O + CO₂↑.
(c)(i) Lime water turns milky due to calcium carbonate: Ca(OH)₂ + CO₂ → CaCO₃↓ + H₂O.
(ii) On passing excess CO₂, the milkiness disappears due to soluble calcium hydrogencarbonate: CaCO₃ + CO₂ + H₂O → Ca(HCO₃)₂.
In simple words: Acid rain eats away marble because marble is calcium carbonate.

Teacher's Note:
1. Value: protecting our heritage by controlling pollution.
2. Write the equation with sulphuric acid.

Question 20. In everyday life, pH plays an important role on daily basis like in gardening and farming, the best crops are usually obtained with neutral or slightly acidic soil (pH 6.5 to 7.0), tooth decay starts when the pH of mouth is lower than 5.5. Bee-sting leaves an acid which causes pain and irritation etc.
(i) During indigestion, which acid is produced by the stomach that causes irritation and pain?
(ii) Rain is called an acid rain when the pH is below which value?
(iii) Which basic salt gives relief on the stung area?
(iv) Which type of medicine is used for the treatment of hyperacidity in the stomach?
(v) Which substance is added by farmers if the soil is acidic: common salt, slaked lime or vinegar?
Answer:
(i) Hydrochloric acid.
(ii) Below 5.6.
(iii) Baking soda (sodium hydrogencarbonate).
(iv) Antacid.
(v) Slaked lime, Ca(OH)₂, because it is basic and neutralises the acidic soil.
In simple words: pH matters in farming, health and teeth.

Teacher's Note:
1. Link each fact to neutralisation.
2. Quote the critical value of pH where it is asked, for example 5.5 for tooth decay.

Question 21. Frothing in Yamuna: The primary reason behind the formation of the toxic foam is high phosphate content in the wastewater because of detergents used in dyeing industries, dhobi ghats and households. Yamuna's pollution level is so bad that parts of it have been labelled dead as there is no oxygen in it for aquatic life to survive.
(i) Predict the pH value of the water of river Yamuna if the reason for froth is high content of detergents dissolved in it: 10-11, 5-7, 2-5 or 7?
(ii) Which is correct for the water with detergents dissolved in it: high concentration of hydroxide ions and low concentration of hydronium ions, or the reverse?
(iii) Solutions P, Q, R and S have pH 2, 9, 5 and 11. Arrange them in increasing order of their hydronium ion concentration.
(iv) What may high content of phosphate ions in river Yamuna lead to?
(v) If a sample of water containing detergents is provided to you, would you neutralise it with baking soda, vinegar, caustic soda or washing soda?
Answer:
(i) 10-11. Detergents are basic, so the pH is greater than 7.
(ii) High concentration of hydroxide ions (OH⁻) and low concentration of hydronium ions (H₃O⁺).
(iii) Lower pH means higher hydronium ion concentration, so S < Q < R < P.
(iv) Decreased level of dissolved oxygen and increased growth of algae (eutrophication), which harms aquatic life.
(v) Vinegar (a mild acid), because detergent water is basic and an acid neutralises it.
In simple words: Basic detergents raise the pH of river water, and phosphates starve water of oxygen.

Teacher's Note:
1. Value: avoid pollution of rivers by using fewer detergents and treating waste water.
2. Use neutralisation for part (v).