National Chemistry

2004 Credit First thoughts

1. (a) B  Oxygen and nitrogen in the air react to produce NO2
(b) A and E  Hydrogen in hydrocarbon forms H2O
carbon in hydrocarbon forms CO2 (not a choice) so CO when
  combustion is incomplete

2. Write the molecular formula C4H8; C5H12; C4H10; C3H8; C2H6 C4H8;
(a) B All melt before 25oC but rest boil before 25oC so are gases
(b) A and F Both C4H8 but different structures
(c) F Alkene has C=C decolourises orange bromine

3. (a) C  Oxides, carbonates and hydroxides
(b) A and C  magnesium hydroxide
(c) A  Write the charge on the ions above each name.
  +2; and -1; +1 and -1; +1 and -1; +1 and -1; +1 and -2; +1 and -1
  Notice B, C , D and F are the same so cannot be a correct answer
  X2+ (Y-)2 = Mg2=(Br-)2

4. (a) D and C
Concentration is the only value changed.

2 mole/l 1 mole/l
  A Zn B Mg
  D Zn C Zn
  F Mg E Mg

Notice that A and B cannot be correct as metal changes as well.
Now add the temperature

  A Zn, 30, B Mg, 30,
  D Zn, 20, C Zn, 20,
  F Mg, 30, E Mg, 20

D and C are possible; so are F and B.
Now look at powder or lump.
  A Zn, 30, B Mg, 30, lump
  D Zn, 20,powder C Zn, 20, powder
  F Mg, 30, powder E Mg, 20

(b) F  Most reactive metal, higher temperature, higher
  concentration and powder

5. (a) A and E conduct when molten or solution not solid
(b) D does not conduct and high melting point

6. (a) C and D  Same atomic number different mass number
(b) A and F   electron arrangement of argon (2.8.8)and for each of the
  six boxes. Some are ions and some are atoms. 2,8,8 (ion) ;
  2,8 (ion) ; 2,8,8,1 ; 2,8,8,1 ; 2,8,8,2 ; 2,8,8 (ion)

7. A and C  no mass, -1 and around nucleus

8. A and F Write list of the five carbohydrates (fructose, glucose,
  maltose, sucrose, starch) and match up what they have in
  common.

A. Glucose polymerises to form starch and water T
B. Starch is made from glucose ?
C. Sucrose does not react with benedict's (first three do)
D. first and fourth are not a pair
E. big starch molecules do not dissolve easily
F. sucrose (number 3) can be broken down T

9. B and D
A. +ve ions do NOT move to +ve electrode - opposites attract F
B. Ni oxidised at +ve electrode - T
C. galvaniSINg uses zinc F
D. oxidation at +ve electrode - Ni loses electrons T
E. electrons along wires F

part 2

10. (a)  view  triple bond to nitrogen not required -CN will do
(b) Carbon monoxide or cyanide

11. (a) A mixture of metals
(b) (i) 5% of 5.74g = 0.287g
(ii) Use figure from part (i).

moles = mass in question  = 0.287   = 0.01 moles
  mass 1 mole 27

12.(a) gas escapes from flask (CO2 produced)
(b)Label the axes using the words in the table. Create scales using at least half the graph paper.
Plot and join the dots.
(c) The amount produced is still 0.80g - it is produced faster
(d) calcium chloride

13.(a) the negative electrons from one atom are attracted to the positive nucleus (protons) of the other atom
(b) (i) The diagram tells you what the dots are. Draw nitrogen out showing only outer 5 electrons. Three hydrogens are required
(ii) You only know one shape. Formula is NH3. draw bonds between the atoms. view

14.
(a)(i) Carbon has double bond to oxygen and two single bonds to two hydrogens. view
(ii)loss of hydrogens
(b) CO

15. Read the information above and below the diagram.
(a) iron to carbon (ferroxyl told you Fe2+ was formed therefore electrons lost).
(b) pH indicator turns blue

16. (a) Ionic solution broken down to elements using electricity
(b) Aluminium to reactive to break compound using heat and carbon
(c) 2Cl- ---> Cl2 + 2e
(d) Tin is less reactive than iron
So iron sacrificially protects the tin

17. (a) (Ag+)2HCO32-
(b) (i)
  3Ag2S + 2Al ---> 6Ag + Al2S3

 working Ag2S + Al ---> Ag + Al2S3
  Ag2S Al Ag
  Ag2S Ag
  Ag
Ag
Ag

(ii) Redox silver ion reduced; alumionium metal oxidised
or displacement aluminium 'kicks out' silver

(c) Mass is mentioned so need mass of 1 mole.
Al2S3 = (2 x Al) + (3 x S) for 1 mole.
= (2 x 27) + (3 x 32) = 150 for 1 mole.

54 g of aluminium in 150g 54  x 100 (for percentage) = 36%
150

18. (a) ammonia has dissolved in the water
(b) above 7 (ammonia is alkali)

19. (a) gas
(b) -5oC

20.Write out molecular formulae - C4H6; C5H8; C6H10 -for each molecule.
(a) Group of molecules with similar chemical properties/same general formula
(b) CnH2n-2
(c) C5H8Br4
(d) cyclo with 4 carbons one pair having a double bond. each carbon has enough hydrogens to make it have 4 bonds.

21.Titration. Circle figures from the diagram ie 0.20 mol/l and 20cm3
(a) indicator changes colour
(b)(i) 20.6 (average of 20.5 and 20.7)

(ii) You now have two figures. 0.20 mol/l from diagram and 20.6 from part (i(0.0206 litres)
concentration = mol  
litre

 therefore  mole = conc x litre

  = 0.2 x 0.0206 = 0.004

(iii) H2SO4 + 2KOH ----> K2SO4 + 2H2O
  1 mole with 2 moles
  0.004 with 2 x 0.00

= 0.008 mol

END

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