Acids, Bases and Salts: Class 7 Science Q&A
34 free answers on Acids, Bases and Salts (Science) for Class 7 students, across CBSE, ICSE and State boards. Includes questions such as “Explain two neutralisation reactions related to a daily life situation.”
Question & Answer
Questions
- ScienceClass 7CBSE
Explain two neutralisation reactions related to a daily life situation.
Soln: A) Acidity Acidity is caused in the stomach as indigestion releases a lot of acids. This can be controlled by taking antacids like milk of magnesia. (b) Ant’s sting Ant’s sting releases formic acid into the skin. It can be neutralised by rubbing baking soda or putting in calamine lotion.
- ScienceClass 7CBSE
Paheli observed that most of the fish in the pond of her village were gradually dying. She also observed that the waste of a factory in their village was flowing into the pond, which probably caused the fish to die. (a) Explain why the fish were dying. (b) If the factory waste is acidic in nature, how can it be neutralised?
Soln: a) As Factory waste is disposed of in the river, it can kill the fish as factory waste may contain acids, bases and other toxic compounds. b) If the factory waste is acidic in nature, it can be neutralised by adding basic substances.
- ScienceClass 7CBSE
You are provided with four test tubes containing sugar solution, baking soda solution, tamarind solution, and salt solution. Write down the activity to find the nature (acidic/basic/neutral) of each solution.
Soln: Add blue litmus solution and then red litmus solution for the test tubes containing sugar solution, baking soda solution, tamarind solution, salt solution. One can observe the colour changes to find the nature of each of them. It is as follows. Sugar and salt solution is neutral as there is no colour change Baking soda turns red litmus to blue and it is a basic solution. Tamarind solution turns blue litmus to red and it is acidic in natur
- ScienceClass 7CBSE
A farmer was unhappy because of his low crop yield. He discussed the problem with an agricultural scientist and realised that the soil of his field was either too acidic or too basic. What remedy would you suggest the farmer to neutralise the soil?
Soln: If the soil is too acidic, it is treated with bases such as quick lime (calcium oxide) or slaked lime (calcium hydroxide). If the soil is too basic, organic matter is added to it. Organic matter releases acids which neutralise the basic nature of the soil.
- ScienceClass 7CBSE
Boojho, Paheli and their friend Golu were provided with a test tube, each containing China rose solution, which was pink in colour. Boojho added two drops of solution ‘A’ in his test tube and got a dark pink colour. Paheli added 2 drops of solution ‘B’ to her test tube and got green colour. Golu added 2 drops of solution ‘C’ but could not get any change in colour. Suggest the possible cause for the variation in their results.
Soln: Since solution A turns China rose colour to dark pink hence Solution A is an acidic solution. solution B turns China rose colour to green colour hence Solution B is a basic solution. Since Solution C did not change the colour of china rose Solution, it is a neutral solution.
- ScienceClass 7CBSE
Fill in the blanks in the following sentences (a) Lemon juice and vinegar taste ___________ because they contain ___________. (b) Turmeric and litmus are _________ acid-base indicators. (c) Phenolphthalein gives _________ colour with lime water. (d) When an acidic solution is mixed with a basic solution, they _________ each other forming _________ and water.
Soln: (a) Lemon juice and vinegar taste sour because they contain acids. (b) Turmeric and litmus are natural acid-base indicators. (c) Phenolphthalein gives pink colour with lime water. (d) When an acidic solution is mixed with a basic solution, they neutralize each other forming salt
- ScienceClass 7CBSE
18. Match the substances in Column I with those in Column II. Column I Column II a) Tartaric acid i) Soap b) Calcium hydroxide ii) Curd c) Formic acid iii) Unripe mangoes d) Sodium Hydroxide iv) Ant’s sting e) Lactic acid v) Lime water
Soln: Column I Column II a) Tartaric acid iii. Unripe mangoes b) Calcium hydroxide v. Lime water c) Formic acid iv. Ant’s sting d) Sodium Hydroxide i. Soap e) Lactic acid ii. Curd
- ScienceClass 7CBSE
Form a sentence using the following words – baking soda, ant bite, moist, effect, neutralised, rubbing.
Soln: The effect of an ant bite can be neutralised by rubbing moist baking soda.
- ScienceClass 7CBSE
While playing in a park, a child was stung by a wasp. Some elders suggested applying the paste of baking soda and other lemon juice as the remedy. Which remedy do you think is appropriate and why?
Soln: Wasp releases a liquid substance into the body when its stings. This liquid will be acidic in nature hence baking soda should be applied as a remedy, and adding lemon juice will increase the pain and redness.
- ScienceClass 7CBSE
Paheli is suffering from indigestion due to acidity. Is it advisable to give her orange juice in this situation, and why?
Soln: No, Orange juice is not advised because orange juice is acidic in nature.
- ScienceClass 7CBSE
Look at the given reaction. Hydrochloric acid + Sodium hydroxide (base) → Sodium chloride (salt) + Water Sodium chloride formed in this reaction remains in solution form. Can we get solid sodium chloride from this solution? Suggest a method (if any).
Soln: Sodium chloride is soluble in water hence we get a solution of sodium chloride. We can get solid sodium chloride by an evaporation method.
- ScienceClass 7CBSE
Which of the following is an acid-base indicator? (a) Vinegar (b) Lime water (c) Turmeric (d) Baking soda
Soln: The answer is (c) Turmeric Explanation: Turmeric will be yellow in the acidic solution and red in the basic solution.
- ScienceClass 7CBSE
On adding the phenolphthalein indicator to a colourless solution, no change is observed. What is the nature of this solution? (a) Basic (b) Either acidic or basic (c) Either acidic or neutral (d) Either basic or neutral
The answer is (c) Either acidic or neutral Explanation: The colour of the phenolphthalein indicator will not change with an acidic or neutral solution.
- ScienceClass 7CBSE
Which of the following set of substances contain acids? (a) Grapes, lime water (b) Vinegar, soap (c) Curd, milk of magnesia (d) Curd, vinegar
Soln: The answer is (d) Curd, vinegar Explanation: Curd contains lactic acid, and vinegar contains acetic acid.
- ScienceClass 7CBSE
A solution changes the colour of the turmeric indicator from yellow to red. The solution is (a) basic (b) acidic (c) neutral (d) either neutral or acidic
Soln: The answer is (a) basic Explanation: Turmeric is acidic in nature hence it is converted to red due to neutralization by the base.
- ScienceClass 7CBSE
A neutralisation reaction is a (a) physical and reversible change. (b) a physical change that cannot be reversed. (c) chemical and reversible change. (d) the chemical change that cannot be reversed.
Soln: The answer is (d) chemical change that cannot be reversed. Explanation: It is a chemical reaction where acid and base react with each other quantitatively. Neutralization is an irreversible process.
- ScienceClass 7CBSE
‘Litmus’, a natural dye, is an extract of which of the following? (a) China rose (Gudhal) (b) Beetroot (c) Lichen (d) Blueberries (Jamun)
Soln: The answer is (c) Lichen
- ScienceClass 7CBSE
When the soil is too basic, plants do not grow well in it. To improve its quality what must be added to the soil? (a) Organic matter (b) Quick lime (c) Slaked lime (d) Calamine solution
Soln: The answer is (a) Organic matter Explanation: Organic matter is added to basic soil to neutralize its base, which improves its quality.
- ScienceClass 7CBSE
Phenolphthalein is a synthetic indicator, and its colours in acidic and basic solutions, respectively, are (a) red and blue. (b) blue and red. (c) pink and colourless. (d) colourless and pink
Soln: The answer is (d) colourless and pink
- ScienceClass 7CBSE
Turmeric is a natural indicator. On adding its paste to acid and base separately, which colours would be observed (a) Yellow in both acid and base. (b) Yellow in acid and red in the base. (c) Pink in acid and yellow in the base. (d) Red in acid and blue in the base.
Soln: The answer is (b) Yellow in acid and red in the base. Explanation: Turmeric paste is yellow in colour, and it is acidic in nature hence it remains yellow in acid, whereas it is converted to red due to neutralization by the base.