National Chemistry

1999 Credit Answers

1. (a) B and F (1 mark)
(b) D (1 mark)

2. (a) D (1 mark)
(b) C and E (1 mark)
(c) D (1 mark)
(d) A and B (1 mark)

3. (a) B (1 mark)
(b) A and C (1 mark)

4. (a) A (1 mark) less reactive metal, lowest temperature; lump; lower concentration</em>
(b) B and C

5. (a) A and D (1 mark)
(b) B and C (1 mark )
(c) F (1 mark )

6. (a) D (1 mark ) metal B must be Fe &amp; more reactive
(b) A (1 mark) biggest gap

7. (a) B and E (1 mark each ) darker, bigger, higher melt/boil pt.

8. (a) A and B (1 mark each) <EM>both conduct electricity
(b) E (1 mark) <em>both give Cl2 but NaCl is neutral

part 2

9. (a) As it moves down the group the atom size increases
(b) As you move along group Li (3), Be (4) B (5) ...etc the atom size decreases
(c) At atomic number 20 - lower than K but higher than number 12's peak

10. (a) to get full outer orbital
(b) Fe3+

11. (a) C3H8S or H8SC3 or C3SH8 etc
(b) Same molecular formula but different structural formulae
(c) carbon dioxide, hydrogen oxide (water) and sulphur (di)oxide
not carbon monoxide as plentiful supply of air

12. First test tube is labelled water with a delivery tube going under the surface; a second delivery tube ,not under the surface, goes to second test tube . The first test tube has stopper on it through which the two delivery tubes pass.

Second test tube is labelled concentrated sulphuric acid with a delivery tube going under the surface; a third delivery tube, not under the surface, goes to the gas jar
The second test tube has stopper on it through which the two delivery tubes pass.

13. (a)
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(b) exothermic
(c)   5 x 12  x 100 (for %)

   60  x 100 = 60 %

14. (a) complete the circuit;
act as an electrolyte;
allow ions to flow.
(b) acidic positive H+ ions turn indicator red as they travel to negative electrode, alkaline negative
OH- ions turn indicator purple as they travel to positive electrode (slower that H+ ions)

15. (a) 4 Ag + O2 + 2 H2S ----> 2 Ag2S + 2H2O

(b) (i) Ag+ + e ----> Ag
(ii) Reduction (gain of electrons)

16. (a) 0.8 (one -OH group always seems to be 0.8)
(b) view

17. (a) Nitrogen unreactive
(b) sodium hydroxide (alkali)
(c) Heat is produced by the reaction itself;
reaction is exothermic
(d) Similar shape

18. (a) nitrogen dioxide at 21; sulphur dioxide at -10; ammonia at -33
(b) ammonia

19. (a) unreactive

(b) 64 g
ie copper sulphide CuS ----> sulphur dioxide SO2
  2 mole of CuS ----> 2 mole of SO2
  2 x (64+32) ----> 2 x 64
  192 g ----> 128 g
  therefore 96 g ----> 64 g

(c) reduce pollution;
remove polluting or poisonous gases turn CO to CO2<; nitrogen oxides to nitrogen

20. (a) biological catalyst
(b) titrate against an acid
(c) As temperature increases the enzyme activity increases then decreases

21. (a) carbonate CO3 2-
(b) Add zinc metal to displace the Cu2+ as brown copper

22. concentration x volume of NaOH = concentration x volume of acid
  20cm3 x unknown = 0.1 mol/litre x 15cm3
  20 x unknown = 1.5
  unknown = 1.5    = 0.075 mol/litre

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