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GCSE Questions and Answers Hard Water

Remember that you can search using “edit”!. GCSE Questions and Answers Hard Water. 6 consecutive GCSE Chemistry papers: 2002-7.

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GCSE Questions and Answers Hard Water

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  1. Remember that you can search using “edit”! GCSE Questions and Answers Hard Water 6 consecutive GCSE Chemistry papers: 2002-7

  2. 2 Water is the most important solvent known to man.a) Give one chemical test for water and the result you would expect to observe if water was present. Test: _______________________________ [1] Observations: ___________________________ ___________________________________ [2] 2002, Paper 2

  3. 2 Water is the most important solvent known to man.a) Give one chemical test for water and the result you would expect to observe if water was present.Test: (anhydrous) cobalt chloride (paper) [1] or anhydrous copper sulphate [1] Observations: Blue [1] to pink [1] or white [1] to blue [1] Hydrated copper (II) sulphate

  4. From “Learning Outcomes”

  5. b) Public water supplies go through two main processes to convert reservoir water to drinking water.(i) Write the name of each process in the blank boxes in the diagram.

  6. b) Public water supplies go through two main processes to convert reservoir water to drinking water.(i) Write the name of each process in the blank boxes in the diagram.

  7. (ii) What is the purpose of chemical process? __________________________ [1]

  8. (ii) What is the purpose of chemical process? Sterilise / kills germs or bacteria [1]

  9. c) A student tested four samples of water (each 5cm3) from different areas of Northern Ireland by shaking with 3 drops of soap solution. Another 5cm3 of each sample of water was boiled and the soap solution test was repeated. The observations were recorded in the table.

  10. From our “Learning Outcomes

  11. Main calcium and magnesium salts causing hardness

  12. (i) Which two samples contain hard water? 1. _____________________ 2. _____________________ [2](ii) Which one sample contains temporary hard water? _______________________________ [1](iii) Explain how you worked out your answer to part (c)(ii). __________________________________ _______________________________ [1]

  13. (i) Which two samples contain hard water? 1. A [1] 2. D [1](ii) Which one sample contains temporary hard water? A [1](iii) Explain how you worked out your answer to part (c)(ii). Hardness removed [1] by boiling [1]

  14. (iv) Explain how temporary hardness arises in rainwater.______________________________ ___________________________ [3](v) Give a balanced symbol equation for the reaction in part (c)(iv). ___________________________ [2]

  15. The two equations may be combined as follows: CaCO3 + H2O + CO2 Ca(HCO3)2

  16. (iv) Explain how temporary hardness arises in rainwater. Reaction [1] between calcium carbonate / CaCO3 / limestone [1] (in rocks) and dissolved carbon dioxide / CO2 [1] in rain water. (v) Give a balanced symbol equation for the reaction in part (c)(iv). CaCO3 + H2O + CO2 → Ca (HCO3)2 or CaCO3 + H2CO3 → Ca(HCO3)2

  17. d) The sample of permanent hard water may be softened using washing soda.i) Explain, in terms of ions, how permanent hard water is softened using washing soda. _________________________________ ______________________________ [3]

  18. Washing soda (sodium carbonate) Calcium + Sodium  Calcium + Sodium Carbonate Carbonate Chloride Chloride CaCl2 + Na2CO3 CaCO3 + Na2CO3 This is the favoured method in industry. The precipitation of Ca2+ and Mg2+ carbonates is instant The sodium salts left behind in their place do not cause hardness

  19. d) The sample of permanent hard water may be softened using washing soda.i) Explain, in terms of ions, how permanent hard water is softened using washing soda. Precipitation/removal [1] of calcium ions/Ca2+ or magnesium ions/Mg2+ [1] by reaction with CO2-3 ions [1] or the calcium ions/Ca2+ or magnesium ions Mg2+ [1] (in the hard water) react with the carbonate ions/CO2-3 [1] (in the washing soda) to form a ppte/of solid (calcium carbonate) [1]

  20. (ii) Give a balanced symbol equation for the reaction in part (d)(i). ____________________________________ [2]

  21. (ii) Give a balanced symbol equation for the reaction in part (d)(i). Equation: Ca2+ + CO2-3 → CaCO3 or Mg2+ + CO2-3 → MgCO3 or Full equation with Na2CO3 and CaSO4/CaCl2/MgSO4/MgCl2

  22. (e) Give two advantages and two disadvantages of hardness in a town’s water supply. Advantages: 1.____________________ 2.____________________ Disadvantages: 1. ___________________ 2. ___________________ [4]

  23. e) Give two advantages and two disadvantages of hardness in a town’s water supply.Advantages: tastes better, used to brew beer, used to tan leather, helps to prevent heart disease. Any two. [2] Disadvantages: produces scum (with soap) produces scale (when boiled), wastes soap, damages delicate fibres. [2]

  24. From our “Learning Outcomes”

  25. 2003, Paper 2 5a) The label below is taken from a bottle of sparkling mineral water and shows the presence and concentration of ions in mg per litre.

  26. (i) Which one of these ions is present in the greatest concentration? ___________________________ [1](ii) Which of these ions is needed to make strong teeth and healthy bones? ___________________________ [1]

  27. (i) Which one of these ions is present in the greatest concentration? Hydrogen carbonate [1](ii) Which of these ions is needed to makes strong teeth and healthy bones? Calcium [1]

  28. (iii) This water is “sparkling”. What gas is used to make it fizzy? _______________________________ [1](iv) Use the information from the label to give the name and formula of two compounds which could be present in this mineral water. [4] Name ___________ Formula __________ Name ___________ Formula __________

  29. (iii) This water is “sparkling”. What gas is used to make it fizzy? Carbon dioxide [1](iv) Use the information from the label to give the name and formula of two compounds which could be present in this mineral water. [4]NameCalcium sulphate [1] FormulaCaSO4[1]NameCalcium chloride [1] FormulaCaCl2 [1]

  30. (v) An open bottle of sparkling mineral water was placed in the fridge for a day, and another placed in sunlight. Which bottle of water will be less fizzy at the end of the day? Explain your answer. __________________________________ __________________________________ _______________________________ [3]

  31. (v) An open bottle of sparkling mineral water was placed in the fridge for a day, and another placed in sunlight. Which bottle of water will be less fizzy at the end of the day? Explain your answer. Bottle in sunlight [1] increase in temperature [1] decrease solubility of gases [1]

  32. It is a good idea to boil tap water to be used to refill a goldfish bowl. This removes any dissolved chlorine that may harm fish. However, it also removes the dissolved air. Leaving the water to cool and sit overnight will give air time to dissolve once again in the water

  33. (vi) Describe how you would find the approximate pH of the sparkling mineral water. _____________________________ ___________________________ [2]

  34. (vi) Describe how you would find the approximate pH of the sparkling mineral water. Universal solution /pH paper [1] compare colour to pH chart [1]

  35. b) 25cm3 samples of water A, B, C and D were tested with soap solution. The volume of soap solution required to produce a lather that lasted for a minute was recorded. Fresh samples of each were boiled and tested again with soap solution. The results are shown below.

  36. i) What is meant by the term “hard water”? _________________________ [2](ii) Which of the four samples contains temporary hardness only? _________________________ [1]

  37. i) What is meant by the term “hard water”?Does not later [1] easily with soap [1](ii) Which of the four samples contains temporary hardness only? Sample D [1]

  38. (iii) Which of the four samples contains both permanent and temporary hardness? Explain your answer. _____________________________ _____________________________ __________________________ [3]

  39. (iii) Which of the four samples contains both permanent and temporary hardness? Explain your answer. Sample C [1] some [1] hardness remained / removed on boiling [1]

  40. (iv) Give a balanced, symbol equation for the reaction taking place when sample D is boiled. ___________________________ [2](v) Ion exchange can be used to soften hard water. Explain, in terms of ions, how this method works. ______________________________ ___________________________ [3]

  41. Ion exchange resins Ca++(aq) + 2Na+(resin)  Ca++(resin) + 2Na+(aq) The ion exchange column is packed with resin beads The beads are “charged with sodium and chloride ions Calcium ions and magnesium ions leave the water and go into the resin beads in exchange for sodium ions. In view of the charges of the ions involved, two sodium ions leave the resin for each calcium or magnesium ion entering the resin The water leaving the resin has no Ca++ or Mg++ ions and is soft water Eventually the resin runs out of Na+ ions.However, the resin can be “recharged” by flushing brine (concentrated NaCl) through it – which reverses the process described above. From “learning Outcomes”

  42. (iv) Give a balanced, symbol equation for the reaction taking place when sample D is boiled.Ca(HCO3)2 → CaCO3 + H2O + CO2 [2](v) Ion exchange can be used to soften hard water. Explain, in terms of ions, how this method works.Calcium ions in hard water [1] exchanged [1] with Na+ ions [1] on resin

  43. 2005, Paper 1 3a) Enniskillen is a limestone region in Northern Ireland famous for its Marble Arch Caves. Water taken from a river near to the caves was found to be hard water, which can be softened by the addition of washing soda.

  44. Stalactites Water constantly drips through cracks in the ceiling of limestone caves Calcium hydrogencarbonate is present, dissolved in the water. A miniscule amount of the calcium hydrogencarbonate in the water undergoes decomposition as the drop hangs from the ceiling.This deposits a miniscule amount of insoluble calcium carbonate on the ceiling It takes about 500 years to grow 1 cm Stalagmites Where the drops of water strike the floor of the cave the same process occurs Pillars When a stalactite and stalagmite eventually meet, they form a pillar Ca(HCO3)2(aq) CaCO3(s) + H2O(l) + CO2(g) This reaction should seem familiar. It explains why boiling removes temporary hardness in water

  45. (i) What is meant by hard water? _______________________________ _______________________________ [2](ii) Describe how you would confirm that the river water contained temporary hardness, giving any observations you would make. _______________________________ _______________________________ _______________________________ [4] Quality of Communication [2]

  46. (i) What is meant by hard water? Does not lather readily [1] with soap [1] [2](ii) Describe how you would confirm that the river water contained temporary hardness, giving any observations you would make. Add soap [1], shake [1], (observe) no lather [1], boil [1], repeat [1] (observe) lather [1] (Max [4]) [4]Quality of Communication [2]

  47. (iii) Explain, in terms of ions, how the addition of washing soda can soften hard water. _______________________________ _______________________________ _______________________________ _______________________________ [4]

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