National Chemistry

1998   Credit Answers

Credit  1998      First thoughts

                            hints

                            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