National Chemistry

1998 Credit Answers

Credit 1998 First thoughts
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  answers

1998 Answers

1. (a) B mass number =Protons + neutrons
(b) D  both 3 orbitals

2.(a) B gain of electrons
(b) D   makes H+
(c) A and C   H+ at the start.

3. Write out the molecular formulae of each box -
CH2O2; C2H6O; C2H4); C2H6O; C3H8O
(a) B and D
(b) C

4. (a) C  Enzymes found in the body - this is digestion.
(b) A and E   hydrogen + nitrogen to make ammonia
  alkene + hydrogen to make alkane

5. (a) C  more volume but still same amount of particles in
  contact at any one time
(b) C and D  increases amount of particles present

6.(a) E 
(b) D and F   acid as reactant; solid formed
  (A = c=C double bond present; B = breaking up hydrocarbon
  C = redox or metal kicks out metal)

7.C and D   creates a barrier; iron protects tin
  (A =iron protects copper; B = colour is blue;
  E -ve protects iron by supplying electrons)

8. A and D  octane does not ignite until 13;
  increases up hexane, heptane, octane
  (B - the C6H12 molecules have different flash points; or same flash point (-21
  but different formula; C = as boiling pt increases flash points do not.)

part 2

9(a) Same atomic number different mass number or
same number of protons different number of neutrons
(b) 6 protons (atomic Number); subtract to get 8 neutrons; electron arrangement 2,4 = 6 electrons
(c) chlorophyll

10. (a) Attraction of positive nucleus for the negative electrons
(b)(i) gains one electron
(ii) ions are strongly bonded together to make a network

11. (a) Zn + Cu2+ -----> Zn2+ + Cu (removeSO4 2-).
(b) Zinc electrode in zinc sulphate solution
copper electrode in copper sulphate solution
salt bridge between the beakers - dipped into solutions
voltmeter connected to the two electrodes

12. (a) To produce carbon monoxide
to burn the carbon
(b) carbon monoxide is a gas - larger surface area.
(c) Fe2O3 + 3CO ---> 2Fe + 3CO2

  Fe2O3 + CO ---> Fe + CO2
  CO Fe CO2
  CO CO2

(d) How much iron is there = 48.3 divided by mass of 56 = 0.86
How much oxygen is there = 41.4 divided by mass of 16 = 2.58
How much carbon is there = 10.3 divided by mass of 12 = 0.86

divide all by lowest number and get : Fe = 1; O = 3; C = 1

answer is FeCO3 (FeO3C)

13.(a)(i) chemical reaction
(ii) Eventually stop working; expensive with resources
(b) loses electrons
(c) supplies ions;

14. i) halogen (group 7 element) on end carbon have a higher boiling point than halogen on inner carbon
ii) further own group the halogen (Cl, Br, I) is the higher the boiling point
higher the atomic number of the halogen is the higher the boiling point

15. (a) As temperature increases the solubility decreases
(b) Higher the temperature the less CO2 dissolved therefore less acid present so pH increases.

16.(a) Alkali - sodium hydroxide
(b) Test for ammonia turns damp pH paper blue
(c) ammonium sulphate (precipitate is barium sulphate)

17. (a) cyclohexanol and phosphoric acid
(b) heat
(c) 70 degrees is less than the boiling points
(d) it has a lower boiling point)

18. (a) (i) Concentration is mol/l ie concentration = mol
  litre

 therefore concentration x litre = moles

10.8cm3 = 0.0108 litre
  concentration x litre = moles
  0.05 x 0.0108 = 0.00054

(ii) (beware introduction of new figure ie 1 litre; diagram also had 1cm3 - it is there for a reason)
 1 silver with 1 chloride. therefore
  0.00054 silver with 0.00054 chloride in 1cm3
therefore in 1 litre 1000cm3 there is 0.54 mole
 
(iii) number of mole = mass in question (the answer)
  mass 1 mole of Cl

  number of mole x mass of 1 mole of Cl = mass in answer

  0.54 x 35.5 = 19.17g

(b) Ag2CrO4 (Ag+ and CrO4 2-)

19. (a) addition ( C=C )
(b) no ions in ethylene glycol
(c) Instead of two OH groups one is just a H (view)

20. (a) the less active the metal in the compound the greater the temperature rise.
(b) 25oC - no reaction with itself!
(c) always 25cm3 ; all chloride of the metals;
(d) copper seen to form

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