1
A student accidentally spills some concentrated acid on their hand while performing an experiment in the lab. Which of the following should be immediately applied to the affected area to provide relief?(a) Soap solution(b) Sodium bicarbonate solution(c) Lemon juice(d) Vinegar3marks
2
A scientist is studying the properties of certain compounds. They observe that one compound, when dissolved in water, produces a solution that turns red litmus blue and feels slippery. Another compound, when reacted with zinc granules, liberates a gas that burns with a 'pop' sound.(a) Identify the type of compound observed first and name one example from the laboratory.(b) Identify the gas liberated in the second observation.(c) Write a balanced chemical equation for the reaction described in (b).4marks
3
Assertion (A): All bases are alkalis, but all alkalis are not bases.Reason (R): Alkalis are bases that dissolve in water.(a) Both A and R are true and R is the correct explanation of A.(b) Both A and R are true but R is not the correct explanation of A.(c) A is true but R is false.(d) A is false but R is true.1mark
4
A village is facing a problem with its water supply. The water has a high pH and tastes bitter. The villagers are experiencing digestive issues.(a) What could be the reason for the high pH and bitter taste of the water?(b) Which type of compound would they need to add to the water to make it suitable for drinking and improve digestion?(c) Name a specific compound that could be used for this purpose and write its chemical formula.4marks
5
A student is performing an experiment to test the acidic or basic nature of different solutions using a pH paper. They observe the following pH values for four different solutions:Solution P: pH = 2Solution Q: pH = 7Solution R: pH = 11Solution S: pH = 13(a) Which solution is strongly acidic?(b) Which solution is neutral?(c) Which solution is weakly alkaline?(d) Arrange the solutions in increasing order of their H+ ion concentration.4marks
6
Consider the following situation:During a cooking class, a chef uses baking soda to make cakes fluffy. Later, the chef uses an antacid tablet to relieve stomach acidity.(a) What is the chemical name of baking soda?(b) Explain how baking soda makes the cake fluffy.(c) Explain how the antacid tablet helps to relieve stomach acidity.5marks
7
Assertion (A): Mixing concentrated sulphuric acid with water is a highly exothermic process.Reason (R): Water has a lower dielectric constant than concentrated sulphuric acid.(a) Both A and R are true and R is the correct explanation of A.(b) Both A and R are true but R is not the correct explanation of A.(c) A is true but R is false.(d) A is false but R is true.1mark
8
A factory produces three useful chemicals: A, B, and C, from the electrolysis of brine.(a) Name the process used for the production of these chemicals.(b) Identify the chemicals A, B, and C.(c) Write the balanced chemical equation for the process.(d) Name one use of chemical A.5marks
9
A farmer notices that the soil in their field is becoming increasingly acidic due to continuous use of chemical fertilizers. This is affecting the growth of their crops.(a) What is the general term used for soil with low pH?(b) Which naturally occurring compounds can be added to the soil to neutralize the excess acid?(c) Write the chemical equation for the reaction between one of these compounds and an acid.4marks
10
A student is given three unknown solutions, X, Y, and Z. They are asked to identify them using indicators.Solution X turns blue litmus red.Solution Y turns red litmus blue.Solution Z does not change the colour of either red or blue litmus.(a) What can be inferred about the nature of solutions X, Y, and Z?(b) If solution Y is an alkali, name one synthetic indicator that would show a distinct colour change in it.(c) What would be the pH range for solution X?4marks
11
Assertion (A): When a metal carbonate reacts with an acid, a salt, carbon dioxide and water are produced.Reason (R): The gas evolved turns lime water milky.(a) Both A and R are true and R is the correct explanation of A.(b) Both A and R are true but R is not the correct explanation of A.(c) A is true but R is false.(d) A is false but R is true.1mark
12
A boy accidentally touches a nettle plant and experiences a burning sensation and pain.(a) Name the acid secreted by the nettle plant.(b) What is the general nature of this acid?(c) Suggest a home remedy to get relief from the pain. Explain why this remedy works.4marks
13
A student is given a sample of washing soda. They perform an activity to verify its composition.(a) What is the chemical formula of washing soda?(b) Describe the activity the student might have performed to confirm the presence of water of crystallisation.(c) Write the chemical equation for the preparation of washing soda from baking soda.5marks
14
A chemist is analyzing two different salts: Salt A is formed from a strong acid and a strong base. Salt B is formed from a strong acid and a weak base.(a) What will be the nature of the aqueous solution of Salt A? Justify your answer.(b) What will be the nature of the aqueous solution of Salt B? Justify your answer.(c) Name one common substance that belongs to the family of salts as Salt A.4marks
15
Assertion (A): Dry HCl gas does not exhibit acidic behaviour.Reason (R): In the absence of water, HCl molecules do not dissociate into ions.(a) Both A and R are true and R is the correct explanation of A.(b) Both A and R are true but R is not the correct explanation of A.(c) A is true but R is false.(d) A is false but R is true.1mark
16
A person uses toothpastes which are generally basic in nature.(a) Why is toothpaste made to be basic?(b) What is the primary component of tooth enamel?(c) What is the critical pH value for tooth decay?3marks
17
A laboratory assistant is preparing solutions for an experiment. They are given concentrated hydrochloric acid and sodium hydroxide pellets.(a) When preparing a dilute solution of hydrochloric acid, what safety precautions should be taken?(b) Describe the process of dissolving sodium hydroxide pellets in water, highlighting any safety concerns.(c) How does the concentration of hydronium ions (H3O+) change when hydrochloric acid is diluted?5marks
18
The image shows a pH paper indicating a specific colour.[Imagine an image of a pH paper strip showing a colour corresponding to pH 1-2].(a) What is the approximate pH value indicated by the colour?(b) What is the nature of the solution?(c) Name a common substance that might have this pH value.3marks
19
Assertion (A): Copper and brass vessels should not be used for storing sour food items like curd.Reason (R): Acids react with copper and brass to form compounds that are toxic.(a) Both A and R are true and R is the correct explanation of A.(b) Both A and R are true but R is not the correct explanation of A.(c) A is true but R is false.(d) A is false but R is true.1mark
20
A group of students is studying the reactions of acids. They observe the following:Test tube 1: Zinc granules + dilute HCl -> Effervescence observed.Test tube 2: Sodium carbonate + dilute HCl -> Effervescence observed.(a) Identify the gas evolved in both test tubes.(b) How can the gas evolved in Test tube 1 be tested for its presence?(c) Write a balanced chemical equation for the reaction in Test tube 2.4marks
Answers
1
(b) Sodium bicarbonate solution. Baking soda solution is alkaline and neutralises the acid spilled on the skin.
2
(a) The first compound is a base or an alkali. Example: Sodium hydroxide (NaOH).(b) Hydrogen gas.(c) Zn(s) + 2HCl(aq) → ZnCl2(aq) + H2(g)
3
(a) Both A and R are true and R is the correct explanation of A.
4
(a) The high pH and bitter taste suggest the water is alkaline, possibly due to dissolved basic compounds. High alkalinity can also cause digestive issues.(b) An acid.(c) Hydrochloric acid (HCl) or an acidic salt that can react to form an acid.
5
(a) Solution P (pH = 2)(b) Solution Q (pH = 7)(c) Solution R (pH = 11)(d) P > R > Q (pH increasing means H+ concentration decreasing)
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(a) Sodium hydrogen carbonate (NaHCO3).(b) When baking soda is heated during cooking, it decomposes to produce carbon dioxide gas. This gas expands and gets trapped in the batter, causing the cake to rise and become fluffy.2NaHCO3(s) Na2CO3(s) + H2O(l) + CO2(g)(c) The stomach produces excess hydrochloric acid during indigestion, causing pain. Antacids contain mild bases that neutralize the excess acid, providing relief. For example, magnesium hydroxide (Milk of Magnesia) neutralizes HCl. Mg(OH)2(s) + 2HCl(aq) → MgCl2(aq) + 2H2O(l)
7
(c) A is true but R is false. (The reason R is incorrect. The heat generated is due to the strong hydration of ions and the breaking of bonds, not solely due to dielectric constant differences.)
8
(a) Chlor-alkali process.(b) A - Sodium hydroxide (NaOH), B - Chlorine gas (Cl2), C - Hydrogen gas (H2).(c) 2NaCl(aq) + 2H2O(l) 2NaOH(aq) + Cl2(g) + H2(g)(d) Chemical A (NaOH) is used in making soaps and detergents, paper manufacturing, and as a cleaning agent.
9
(a) Acidic soil.(b) Calcium oxide (quick lime), Calcium hydroxide (slaked lime), or Calcium carbonate (chalk/limestone).(c) Example reaction with quick lime: CaO(s) + 2HCl(aq) → CaCl2(aq) + H2O(l)
10
(a) Solution X is acidic. Solution Y is basic. Solution Z is neutral.(b) Phenolphthalein (turns pink in basic solution) or Methyl orange (turns yellow in basic solution).(c) pH < 7 (typically between 1 and 6 for acidic solutions).
11
(a) Both A and R are true and R is the correct explanation of A.
12
(a) Methanoic acid (or formic acid).(b) It is an acidic substance.(c) Rubbing the affected area with the leaf of the dock plant. The dock plant is alkaline in nature and neutralizes the methanoic acid, providing relief.
13
(a) Na2CO3·10H2O.(b) The student would heat a few crystals of washing soda in a dry test tube. If water of crystallisation is present, water droplets will be observed on the cooler parts of the test tube, and the white anhydrous salt (Na2CO3) will be left behind. Adding a few drops of water to the anhydrous salt will restore its blue colour.(c) 2NaHCO3(s) Na2CO3(s) + H2O(l) + CO2(g)Na2CO3(s) + 10H2O(l) Na2CO3·10H2O(s)(Note: The preparation of washing soda often involves the Solvay process which starts from NaCl, NH3, and CO2 to produce NaHCO3, then heating NaHCO3 to get Na2CO3, and finally recrystallizing Na2CO3 to get washing soda. The question asks for preparation from baking soda, hence the two steps provided.)
14
(a) The aqueous solution of Salt A will be neutral. This is because it is formed from the reaction of a strong acid and a strong base, both of which completely dissociate, resulting in a balanced concentration of H+ and OH- ions.(b) The aqueous solution of Salt B will be acidic. This is because it is formed from a strong acid and a weak base. The strong acid will dissociate completely, contributing more H+ ions, while the weak base will dissociate partially, contributing fewer OH- ions, leading to an excess of H+ ions.(c) Sodium chloride (NaCl).
15
(a) Both A and R are true and R is the correct explanation of A.
16
(a) Toothpaste is made basic to neutralize the acids produced by bacteria in the mouth after eating food, thus preventing tooth decay.(b) Tooth enamel is primarily made up of Calcium hydroxyapatite [Ca10(PO4)6(OH)2].(c) The critical pH value for tooth decay is below 5.5.
17
(a) Safety precautions include wearing safety goggles and gloves, adding the concentrated acid slowly to water with constant stirring, and performing the dilution in a fume hood.(b) Wear safety goggles and gloves. Add water to a beaker and then slowly add the sodium hydroxide pellets to the water with constant stirring. The beaker will become warm due to the exothermic nature of the dissolution process. Avoid adding water to the pellets directly as it can cause splashing.(c) When hydrochloric acid is diluted, the concentration of hydronium ions (H3O+) decreases because the same number of H3O+ ions are now present in a larger volume of water.
18
(a) The approximate pH value indicated is 1 or 2.(b) The solution is strongly acidic.(c) Concentrated hydrochloric acid (HCl) or dilute sulphuric acid (H2SO4).
19
(a) Both A and R are true and R is the correct explanation of A.
20
(a) In both test tubes, the gas evolved is carbon dioxide (CO2). (Note: While hydrogen gas is evolved when acid reacts with metals, the effervescence in the context of metal carbonates reacting with acids is specifically carbon dioxide).(b) The gas evolved in Test tube 1 can be tested by passing it through lime water (calcium hydroxide solution). If the gas is hydrogen, it will burn with a 'pop' sound when a burning candle is brought near it. (Correction: The question asks about effervescence. When acids react with metals, hydrogen gas is evolved, and it burns with a pop. When acids react with metal carbonates, carbon dioxide is evolved, which turns lime water milky. Assuming the intent of the question is to test for the evolved gas, for test tube 1, the gas is Hydrogen. For test tube 2, the gas is Carbon Dioxide.)Let's re-evaluate based on typical NCERT experiments:Test tube 1 (Zinc granules + dilute HCl): Gas evolved is Hydrogen (H2). Test: Bring a burning candle near the mouth of the test tube. The gas burns with a 'pop' sound.Test tube 2 (Sodium carbonate + dilute HCl): Gas evolved is Carbon Dioxide (CO2). Test: Pass the gas through lime water (Ca(OH)2). The lime water turns milky.Therefore, for question 20:(a) In Test tube 1, the gas evolved is Hydrogen (H2). In Test tube 2, the gas evolved is Carbon Dioxide (CO2).(b) The gas evolved in Test tube 1 (Hydrogen) can be tested by bringing a burning candle near the mouth of the test tube. The gas burns with a 'pop' sound.(c) Na2CO3(s) + 2HCl(aq) → 2NaCl(aq) + H2O(l) + CO2(g)
