National Chemistry

2001 Credit HINTS

1. (a) These are all coatings- sacrificial protection uses another element to protect the iron.
  (b) The opposite of sacrificial protection but again using another element.
  Page 7 of the data book may help.

2. A time consuming question but should be easy to get correct.
(a) Changing particle size
    powder ribbon
  A C
  B F

MUST be one box from the powder column and one box from the ribbon column - everything else must be the same.
Write the temperatures beside each box letter

powder  ribbon
  A 20 C 40
  B 20 F 20
  D 20
  E 20

Must be F and A or B or D or E ie C is not part of the answer
Write the concentration beside each letter to eliminate some combinations.
remember to pick 2 boxes

(b) Looking for an unreactive metal.

3. (a) Neutrons are the one that has to be calculated from the figures given in this style of representing the atom
remember to pick 2 boxes

(b) The definition of an isotope is a MUST KNOW
If you are picking TWO isotopes then the boxes chosen must have something in common.
eg boxes A and B have nothing in common to explain why you would pick them.
remember to pick 2 boxes

(c) Electron arrangements are shown in page 1 of the data book
- find neon and write down its electronnic configuration
- find each of the rest and write down their electronic configuration
remember to pick 2 boxes

4. It is very important to recognise Chemical reactions.

(a) What is yeast used to make ?
(b) What occurs during hydrolysis
(c) Some are in plants
Obviously a different answer for each question - so getting the answer to any will eliminate an answer for another.
You could try naming any of the reactions to eliminate wrong answers.

5. (a) bases neutralise acids.
remember to pick 2 boxes

(b) Use page 5 of data book - look each up separately - only one will form a precipitate

6. Modern exam papers would tell you this was worth 2 marks which means TWO correct answers.
Find which boxes contain true statement for protons
Find which boxes contain true statements for neutrons

7. Modern exam papers would tell you this was worth 2 marks which means TWO correct answers.
X and Y will both need to be conductors
Tick the conductors in column X
Tick the conductors in column Y
Hopefully there will be TWO experiments both with conductors

8. Modern exam papers would tell you this was worth 2 marks which means TWO correct answers.
In this style of question then there are TWO correct answers and three wrong answers
- work through each statement individually deciding if it is True/ False.
see page 8 of the data book to identify transition metals
A find the colours associated with copper ions and nitrate ions
B look at four of the coloured ions
C check that the four containing oxygen are all colourless
D check the three transition metals<BR>
E Li is colourless - will all lithium compounds be colourless

9. Modern exam papers would tell you this was worth 2 marks which means TWO correct answers.
In this style of question then there are TWO correct answers and three wrong answers
- work through each statement individuaally deciding if it is True or False.
A Which substances in the table are compounds and which are elements ?<BR>
B Relative formula mass increases in the third column. Does critical temperature also increase ?
C Elements for A. Which are diatomic elements which are monatomic (noble gases)<BR>
D Carbon dioxide becomes a liquid below its critical temperature

part 2

10. If bromine water is quickly decolourised then a C=C is present
(a) Can C5H12 be drawn out with a C=C
(b) Draw out hydrocarbon B remembering that it does not decolourise bromine water.
(c )from the table what do C and D have in common ?

11. (a) A metal reacts with H2O - what possible gases ?
(b) Y to reacts with water - how reactive is this ?
W needed only heat to beak up the oxide - how reactive is this ?
(c) Only Y reacted with water
Only W was obtained by heating alone
X "kicked out" or displaced Z
Most reactive first

(d) A metal oxide like ZnO produces Zn

12. (a) Remember that you can only put figures in front of the formulae - you CANNOT change any of the formula you have been given.
(b) Must be removed for a reason - cannot be good.
(c) Underline the chemicals mentioned in the question ie sulphur S and hydrogen sulphide H2S (first line told you formula of hydrogen sulphide).
H2S -------> S
Write under this the number of moles
  2 mole of H2S -------> 3 mole of S
Write under this the mass of these moles

(d) (i) label both axes; put on the scale; make sure over half the graph paper is
  used; make sure it is a line graph.
  (ii) When making a statement about a relationship given in a graph you can usually frame your answer as follows "As the data along the way
 increases then the data up the way
 increases or decreases (pick one)

13. (a) (i) The data book will identify these ions - page 4
(ii) For plants ?
(b) Acids make the second name - nitrate in this case.
(c) (i) Thermosetting thermo for "heat"
(ii) How much N in CO(NH2)2 ?
then mass of nitrogen   x 100%
  mass of CO(NH2)2

14. (a) The data in the Dead Sea column is different from the data in the Ocean water column - in what way ?
(b) Remove the water - suggest something left behind.
(c) Ocean water has 0.4 g of Ca2+
How many mole of calcium is 0.4 g ?

15. (a) Mark it on the diagram - it is either right to left or left to right
Use page 7 of the data book.

(b) (i) electrons in the equation means a half equation - use page 7 of the data book<BR>
(ii) for pH watch for H+ or OH-

(c) Beaker A has Br2 - look for this on page 7

16. (a) Common catalysts you should know are iron, platinum, yeast, aluminium oxide.
(b) Ammonia is NH3 - notice that it asks for compounds
(c) Want to talk about electrons - what else is present in atoms ?

17. (a) Alkanes is another example of a homologous series

(b) (i) X must contain something that is in the reactants ie C or H or Br or Na but not Cl.
(ii) each C makes 4 bonds; each H has one bond; each O has two bonds - just draw
as written.
18. (a) Find the reactor.
Mg2+ (aq) reacts with calcium hydroxide to produce solid magnesium hydroxide

(b) Use ions in data book - page 7 and page 4

(c) From the diagram
 magnesium oxide + carbon + chlorine ----->; gas X + magnesium chloride
Gas X must be formed from something on the left hand side eg cannot be bromine

(d) Why can they not do it when solid ?

19. (a) Work out the molecular formula for propyne and butyne

(b) (i) Look carefully at the reaction given as an example.
What happens to dibromoalkane when it appears on the right hand side - 3 C are still
(ii) This molecule does not react so it must be different from the dibromoalkane example

End of hint area

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