Chemical Families

12 Grade 10 General Science questions on Chemical Families, with worked marking schemes. 12 questions are available on this topic in full.

1. Question 1

   1 mark

   Which statement correctly describes the physical states of chlorine, bromine and iodine at room temperature?

   A. Chlorine is a liquid, bromine a gas and iodine a solid

   B. Chlorine is a gas, bromine a liquid and iodine a solid

   C. Chlorine and bromine are gases while iodine is a liquid

   D. All three are pale-coloured gases made of diatomic molecules

   (1 mark)

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2. Question 2

   1 mark

   Which gas is used in advertising signs because it glows red-orange when an electric current is passed through it at low pressure?

   A. Helium

   B. Argon

   C. Chlorine

   D. Neon

   (1 mark)

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3. Question 3

   1 mark

   Potassium reacts more vigorously with cold water than sodium does. This is because the potassium atom

   A. has more electrons in its outer energy level

   B. loses its outer electron more easily

   C. gains electrons more readily from water

   D. has a smaller atom than a sodium atom

   (1 mark)

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4. Question 4

   5 marks

   The following elements are among the first twenty elements of the periodic table (atomic numbers in brackets): helium (2), beryllium (4), fluorine (9), neon (10), magnesium (12), chlorine (17), argon (18), calcium (20)

   (a) Draw a table with the headings "Chemical family" and "Elements", and use it to classify the elements above into their chemical families. (4 marks)

   (b) Give a reason why beryllium and calcium belong to the same chemical family. (1 mark)

   (5 marks)

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5. Question 5

   3 marks

   Sodium vapour lamps have been widely used to light roads and highways.

   (a) State the colour of the light given out by a sodium vapour lamp. (1 mark)

   (b) Explain two ways in which the light from these lamps contributes to road safety. (2 marks)

   (3 marks)

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6. Question 6

   6 marks

   A teacher removed a piece of sodium from the paraffin oil in which it is stored, cut a small piece from it on a white tile, and dropped the small piece into a trough of water containing a few drops of phenolphthalein indicator.

   (a) State one physical property of sodium shown when it is cut with a knife. (1 mark)

   (b) State two observations made in the trough. (2 marks)

   (c) Write a balanced chemical equation for the reaction between sodium and water. (2 marks)

   (d) State one safety precaution, other than the method of storage, that the teacher should observe. (1 mark)

   (6 marks)

   Marking scheme

   (a) Any one (1 mark): - It is soft and easily cut with a knife - The freshly cut surface is shiny/silvery - The shiny surface quickly tarnishes (turns dull) in air (b) Any two, 1 mark each (2 marks): - Sodium floats on the water - It melts into a silvery ball - It darts about on the surface - A hissing/fizzing sound is heard (effervescence) - The piece decreases in size and finally disappears - The water turns pink around the sodium (c) 2Na(s) + 2H₂O(l) → 2NaOH(aq) + H₂(g) - Correct formulae (1 mark) - Correctly balanced (1 mark) (d) Any one (1 mark): - Use only a very small piece of sodium - Handle sodium with forceps/tongs, not bare hands - Wear safety goggles - Use a safety screen or keep learners at a safe distance - Do not cover the trough or lean over it - Return unused sodium to the paraffin oil immediately

7. Question 7

   4 marks

   A piece of moist blue litmus paper was lowered into a gas jar full of chlorine.

   (a) State the observation made. (1 mark)

   (b) Write a balanced chemical equation for the reaction between chlorine and water. (2 marks)

   (c) Explain why experiments with chlorine are carried out in a fume cupboard or in the open air. (1 mark)

   (4 marks)

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8. Question 8

   4 marks

   Explain how the properties of each of the following gases make it suitable for the use given.

   (a) Helium is used to fill weather balloons. (2 marks)

   (b) Argon is used to fill electric filament bulbs. (2 marks)

   (4 marks)

   Marking scheme

   (a) Any two, 1 mark each (2 marks): - Helium has a very low density (it is much lighter than air), so the balloon rises - It is unreactive/inert - It is non-flammable, so it is safer than hydrogen (b) Any two, 1 mark each (2 marks): - Argon is unreactive/inert, so it does not react with the very hot tungsten filament and the filament does not burn away (oxidise) - It replaces air (oxygen) in the bulb, so the bulb lasts longer - It is the most plentiful noble gas in air, so it is cheap enough to use in large numbers of bulbs (Points must relate the property to the use; a property stated alone scores 1 mark maximum per part.)

9. Question 9

   4 marks

   Iron and zinc are among the most widely used metals in Kenya. For each metal, outline one use and the property that makes the metal suitable for that use.

   (a) Iron (2 marks)

   (b) Zinc (2 marks)

   (4 marks)

   Marking scheme

   For each metal: 1 mark for a correct use and 1 mark for a matching property. (a) Iron, any one pair: - Making steel for building, bridges, railway lines and roofing sheets; it is strong (high tensile strength), hard and malleable - Making tools, nails and machinery; it is strong and hard - Making jikos (charcoal stoves) and cast-iron cooking pans; it conducts heat well and has a high melting point (b) Zinc, any one pair: - Galvanising iron roofing sheets (mabati) to prevent rusting; zinc is more reactive than iron so it corrodes in preference and forms a protective layer - Making the casing (negative electrode) of dry cells; it conducts electricity and is a fairly reactive metal - Making brass (with copper) for taps and fittings; the alloy is hard and resists corrosion

10. Question 10

    1 mark

    Elements with atomic numbers 3, 11 and 19 are placed in the same chemical family. Which family is it?

    A. Halogens

    B. Alkaline earth metals

    C. Noble gases

    D. Alkali metals

    (1 mark)

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11. Question 11

    6 marks

    A Grade 10 learner investigated the reactions of magnesium ribbon with air and with dilute hydrochloric acid.

    (a) Explain why the magnesium ribbon was cleaned with sandpaper before it was burned in air. (1 mark)

    (b) Write a balanced chemical equation for the burning of magnesium in air. (2 marks)

    (c) A piece of clean magnesium ribbon was then dropped into dilute hydrochloric acid in a test tube.

    (i) State one observation made. (1 mark)

    (ii) Write a balanced chemical equation for the reaction. (2 marks)

    (6 marks)

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12. Question 12

    1 mark

    Copper is widely used for electrical wiring in homes. Which property of copper makes it suitable for this use?

    A. It has a low melting point and is brittle

    B. It forms a protective coat that conducts no current

    C. It reacts rapidly with dilute acids to give hydrogen

    D. It conducts electricity well and is ductile

    (1 mark)

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