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 %)

                  100

 

                     60     x 100   =  60 %

                100

 

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

                                                                         20

Credit  1999      Hints

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