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Class 10 Chemistry Chapter 20 Water Test 5 | Punjab Board 2027
Grade 10 Chemistry Chapter 20 Water
Prepare for the Punjab Board Class 10 Chemistry Examination 2027 with Chapter 20: Water – Class Test No. 5. This test covers Topics 20.1 to 20.5 and is designed to support students preparing for the 10th Class Chemistry annual examination according to the new syllabus issued by PECTAA Punjab. As part of our Punjab Board 2027 Model Papers, Full Unit Model Papers, and Chapter-Wise Test Series, this Chemistry practice test helps students revise important concepts, assess their understanding of the chapter, and improve their examination preparation. Practice Class 10 Chemistry Chapter 20 Water Test 5 to strengthen your subject knowledge and prepare effectively for the 2027 board examinations.
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Chapter Wise Class Test
T-5
Chapter-20
Water
1.The colour of hydrated copper sulphate is:
(a) White(b) Pink(c) Blue(d) Green
2.The presence of impurities in a sample of water causes the boiling point to:
(a) Decrease slightly(b) Increase slightly(c) Remain at 100°C(d) Drop to 0°C
3.Freezing point of water is:
(a) 0°C(b) 10°C(c) 100°C(d) 105°C
4.Requirement of micronutrients per acr is
(a) 15kg – 200kg(b) 6g – 200g(c) 1kg – 5kg(d) 200g – 1000g
5.Which conclusion can be drawn from the fact that distilled water has pH 7?
(a) It is acidic(b) It is basic(c) It is neutral(d) It is alkaline
6.The health and diversity of an aquatic ecosystem depend upon:
(a) Water temperature(b) Amount of dissolved oxygen(c) Water colour(d) Water pressure
7.Which disease is caused by contaminated water?
(a) Asthma(b) Diabetes(c) Cholera(d) Cancer
8.In sedimentation, suspended particles settle down due to:
(a) Heating(b) Pressure(c) Gravity(d) Filtration
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Chapter Wise Class Test
T-5
Chapter-20
Water
(i)Which chemical is used to test the presence of water?
Ans: Anhydrous copper(II) sulphate (CuSO4). It turns from white to blue in the presence of water.
(ii)How do impurities affect the boiling and melting point pure water?
Ans: Impurities slightly increase the boiling point of water (above 100°C) and lower its melting/freezing point (below 0°C).
(iii)Why is tap water not considered pure?
Ans: Tap water contains dissolved minerals, salts, gases and traces of chlorine and other impurities, so it is not pure water.
(iv)What is dissolved oxygen and how does it enter natural water?
Ans: Dissolved oxygen is oxygen gas present in water. It enters natural water by diffusion from the air and by photosynthesis of aquatic plants and algae.
(v)How do heavy metals affect human health after entering water bodies?
Ans: Heavy metals such as lead, mercury, arsenic and cadmium enter the food chain and accumulate in the body, damaging the brain, kidneys, liver and nervous system and may cause cancer.
(vi)Difference between useful and harmful substances present in natural water.
Ans: Useful substances (dissolved oxygen, minerals and nutrients) support aquatic life and human health. Harmful substances (microbes, heavy metals, pesticides, plastics) cause diseases and pollute the water.
(vii)What is the difference between suspended impurities and dissolved impurities?
Ans: Suspended impurities are insoluble particles (sand, clay) that can be removed by sedimentation or filtration. Dissolved impurities (salts, gases) are mixed at molecular level and need methods like distillation.
(viii)What is Chlorination, and why is it considered the most vital step for human safety?
Ans: Chlorination is the addition of chlorine to water. It kills harmful bacteria and microbes, so it prevents water-borne diseases like cholera and typhoid.
(ix)Why tap water is a conductor of electricity whereas distilled water is not?
Ans: Tap water contains dissolved salts that form free ions which carry current. Distilled water has no dissolved ions, so it does not conduct electricity.
3.Why water is important. Describe the chemical test for the presence of water using anhydrous copper (II) sulphate.
Ans: Water is essential for life: it is needed for drinking, digestion, transport of nutrients, agriculture, industry and for aquatic life.
Test: Add a few drops of the liquid to white anhydrous copper(II) sulphate. If water is present, the white powder turns blue (hydrated copper(II) sulphate).
CuSO4 + 5H2O → CuSO4·5H2O (white → blue)
Test: Add a few drops of the liquid to white anhydrous copper(II) sulphate. If water is present, the white powder turns blue (hydrated copper(II) sulphate).
CuSO4 + 5H2O → CuSO4·5H2O (white → blue)
4.Describe how the purity of water can be determined by measuring its boiling point and freezing (melting) point under standard conditions.
Ans: Pure water boils at exactly 100°C and freezes at 0°C at standard pressure (1 atm). Heat the sample with a thermometer and note when it boils, then cool it and note when it freezes. If the boiling point is higher than 100°C and the freezing point is lower than 0°C, the water contains impurities. The larger the difference, the more impure the water.
