Acids, Bases and Salts
11 Grade 10 General Science questions on Acids, Bases and Salts, with worked marking schemes. 11 questions are available on this topic in full.
Question 1
4 marksOutline one application in day-to-day life of each of the following salts:
(a) sodium chloride (1 mark)
(b) sodium hydrogencarbonate (1 mark)
(c) calcium sulphate (1 mark)
(d) sodium carbonate (1 mark)
(4 marks)
Marking scheme
1 mark for any one correct application of each salt (4 marks): (a) Sodium chloride: seasoning food; preserving fish and meat; making soap; melting ice on roads; oral rehydration solution / saline drip in medicine (b) Sodium hydrogencarbonate: baking powder to make dough rise (food industry); antacid to relieve indigestion (medicine); in some fire extinguishers (c) Calcium sulphate: plaster of Paris for casts on broken limbs (medicine); making chalk and building plaster; supplying calcium and sulphur to soil (agriculture) (d) Sodium carbonate: washing soda for softening hard water in laundry; making glass; making soaps and detergents Total: 4 marks
Question 2
5 marks(a) Fertilisers containing nitrate and phosphate salts are washed by rain from farms into Lake Victoria. Explain how this can lead to the death of fish in the lake. (3 marks)
(b) Outline two reasons why people should limit the amount of table salt they add to food. (2 marks)
(5 marks)
Marking scheme
(a) 1 mark each (3 marks): - The salts act as plant nutrients, causing rapid growth of algae and water weeds such as water hyacinth (eutrophication / algal bloom) - The plants cover the surface and block light; when they die, bacteria decompose them and use up the dissolved oxygen - Fish die due to lack of dissolved oxygen (b) Any two of the following, 1 mark each (2 marks): - Too much salt raises blood pressure (hypertension) - It increases the risk of heart disease and stroke - It can damage the kidneys - It causes the body to retain water (swelling) Total: 5 marks
Question 3
1 markA person with indigestion caused by excess stomach acid takes an antacid tablet containing magnesium hydroxide. The tablet relieves the discomfort because it
A. coats the stomach wall so no acid forms
B. dilutes the acid by adding water to it
C. neutralises some of the stomach acid
D. kills the bacteria that produce the acid
(1 mark)
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Create a free account to see itQuestion 4
4 marksA farmer in Kisii tested a soil sample and found that its pH was 4.5. Maize grows best in soil with a pH of 6.0 to 7.0.
(a) State whether the soil is acidic, neutral or basic. (1 mark)
(b) Name one substance the farmer could add to make the soil suitable for maize, and explain how it works. (2 marks)
(c) Explain why the farmer should not add too much of the substance named in (b). (1 mark)
(4 marks)
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Create a free account to see itQuestion 5
4 marksAcids play important roles in the human body. Explain the role of:
(a) hydrochloric acid in the stomach during digestion (2 marks)
(b) carbonic acid formed in the blood in the control of breathing. (2 marks)
(4 marks)
Marking scheme
(a) Any two of the following, 1 mark each (2 marks): - Provides an acidic medium (about pH 2) in which the enzyme pepsin works best - Activates pepsinogen to pepsin, which digests proteins - Kills harmful microorganisms taken in with food - Stops the action of salivary amylase (b) (2 marks) - Carbon dioxide produced in respiration dissolves in blood plasma to form carbonic acid, which lowers the pH of the blood (1 mark) - The fall in pH is detected by the brain (respiratory centre), which increases the rate and depth of breathing to remove the excess carbon dioxide (1 mark) Total: 4 marks
Question 6
1 markWhich pair of substances reacts to form potassium sulphate and water only?
A. potassium chloride and dilute sulphuric acid
B. potassium hydroxide and sulphur dioxide
C. potassium nitrate and sulphuric acid
D. potassium hydroxide and sulphuric acid
(1 mark)
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Create a free account to see itQuestion 7
1 markWhich observation shows that a solution contains more hydroxide ions than hydrogen ions?
A. it turns blue litmus paper red
B. its pH reading is 4
C. universal indicator turns blue in it
D. it fizzes when added to sodium carbonate
(1 mark)
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Create a free account to see itQuestion 8
1 markDilute nitric acid is added to calcium carbonate in a beaker. Which products are formed?
A. calcium nitrate, carbon dioxide and water
B. calcium oxide, water and nitrogen dioxide
C. calcium nitrate and hydrogen gas only
D. calcium hydroxide, carbon dioxide and hydrogen
(1 mark)
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Create a free account to see itQuestion 9
1 markA learner tested four household substances with universal indicator and compared the colours with a pH chart. Which substance most likely gave a pH of about 3?
A. sugar solution
B. toothpaste solution
C. milk of magnesia
D. vinegar
(1 mark)
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Create a free account to see itQuestion 10
4 marksDescribe how a learner would use universal indicator solution and a pH chart to find the pH of a sample of lemon juice in the laboratory.
(4 marks)
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Create a free account to see itQuestion 11
5 marksSamples of three salts, J, K and L, were weighed in open watch glasses, left on the laboratory bench for two days and then weighed again. The observations were: - J: the mass increased and the salt remained a solid. - K: the mass increased and the salt changed into a solution. - L: the mass decreased and the crystals turned into a white powder.
(a) Classify each salt according to its behaviour when exposed to air. (3 marks)
(b) Suggest how salt K should be stored in the laboratory, and give a reason. (2 marks)
(5 marks)
Marking scheme for this question
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