National Chemistry

2005 Credit Almost the answers

1. (a) Look up data book - page 4
(b) Write electronic arrangements in the boxes of the atoms.
 2,8 ; 2,8,8,1 ; 2,8,2 ; 2,8,7; 2,8,5; 2,8,6
What is the electronic arrangement of the calcium ion?
The atom is 2,8,8,2 so the ion is ......
(c) What elements in a covalent compound? Must be non-metals therefore only D, E and F.
What are the bonds made by each of these ?
It may help to know how many bonds carbon needs?

2.(a) What fuel is camping gas ? If fuel is used as a gas it is not a liquid. How many carbons in liquid petrol ?
(b) Highest must be at top or bottom - must be an extreme.
Really thick liquid in fact almost tarry. 1 C or 20 Cs that's the choice.

3. The carbohydrates are listed in the correct order
(a) Which carbohydrate is not paired up?
If it does not dissolve well it must be biggest
(b) One of the pairings. What does 'di' suggest - 2nd pairing perhap?

4. (a) Must have boiled before 0oC ie less than zero.
(b) molOWcules - TWO with low melting points.
Reduces it to four substances - A, B?, C, and E. You would expect the 'conducts' columns to be the same for both molecules A, E and F.

5. Molecular formula written in each box
C4H10,, C3H6, C4H10, C4H10, C4H8, C4H8, C3H6
(a) Must be made from propene. How many carbons in propene - page 6 = 3 What else is required for polymerisation.
(b) Need to match general formula which tells you 'double number of hydrogens' - B, D, E & F and not react with bromine. What does react with bromine ?
(c) Write the molecular formula of substance asked about. C4H8
Any two silmilar to this ?

6. Electrons at the right hand side.
use page 7 - which shows electrons on the left hand side as (look at top of page)

7. Beware of statements that are true for only one of the acids.
Treat as true/false statements for each acid.
A. Do acids react with Mg ? YES
B. do acids have pH less than 7 ?YES
C. do acids conduct electricity ? YES
D. do these acids contain chlorine ? hydrochloric might, sulphuric does not.
E do acids contain more hydrogen ions than pure water YES

8. Rewrite metals in a column, as on page 7, because that is the way you are used to. It is near the bottom.
Read the boxes in terms of reactivity
A. X reacts faster than copper - X is lower !!!
B. Oxide of X harder to beak down than silver oxide - X is higher
C. Magnesium kicks out X - X is lower
D. X more reactive than nickel - X is lower !!!!
E. Compounds of X easier to destroy than compounds of zinc - X is lower

9. Check the ones involving iron first.
Rusting is oxidation - any examples of iron being oxidised ? Yes one.
What about reduction ?

Part 2

10. (a) (i) Copy from the data book.
Oxidation is loss (OIL) Opposite direction for oxidation
(ii) protection !! Zinc protecting steel (iron). Poor old zinc it is corroding.
(b) use page 7.
Cobalt makes the steel (iron) rust; zinc did not let the iron rust. So cobalt must be different from zinc.

11. (a) You need three monomers together - how many carbons along the backbone ?
  3 x 2 = 6 C joined is the main structure
Add on the up and down parts as shown in question.
(b) Write the molecular formula of the molecule. C8H8
How much carbon out of whole structure ?

  =  98  

12. (a) There are three formula so you should be able to work out a general formula using 'n' instead of numbers. CH4, C2H6, C3H8 = CnH......
(b) (i) Page 6 goes up to octane (126oC)so deduce one for nonane. Not too high.
(ii)Cannot say 'speed up the reaction'. Heat?
(c) Concentrate on the carbons in each molecule
  ie 2 x carbon + 2 x carbon ------> 4 x carbon
  1 x C + 3 x C

13. Read the question. It is long but straight forward.
(a) (i) Look at graph - the example had 2 isotpes.
(ii) Same as the example - different figures
  example reads
   (mass of isotope A x %) + (mass of isotope B x %)

 from the graph this is  (35 x 75) + (37 x 25)

Use figures from second graph (6 x 10) + (? x ?)

(b) Neutrons by subtraction
Protons are given
You are being asked about an ion.
Get electronic configuration for the atom from the data book and make it an ion.

14. (a) You have done this experiment with sulphuric acid.
Why is there solid remaining? It cannot have reacted.
(b) How do you make it into solid crystals?
Get rid of that solid. Get rid of the water

15. (a) Get electronic arrangement of nitrogen. You need two of them for N2
Draw TWO circles to represent the outer electrons only and overlap them.
(b) (i) What were the two processes in nitrogen chemistry? Haber and Oswald - which is it?
(ii) Not a lot of information. Question suggests that you still want heat. Why would you be able to stop heating something that still wants heat ? Heat must be coming from somewhere else.

16. (a) Rewrite on paper so you can do the working.
One H on both sides, one Cl on both sides - Na causes first problem

HCl + Na2S2O3 ----> NaCl + S + SO2 + H2O
Need to go back to chlorine

HCl + Na2S2O3 ----> NaCl + S + SO2 + H2O
HCl NaCl

Check rest

(b)(i) Label axes and make scales. First column goes along the x axes
need to use half the graph paper
need to do a line graph
(ii) Extend the line to meet 60oC
(iii) as ' temperature' increases speed (beware it is speed not time) .......
(c) Look at diagram - does it suggest anything. You have changed temperature so do not pick that.
What about the solutions?

17. (a) Carbohydrates listed in Q3 - Glucose is first= 6C
(b) (i) Think on chemical reactions that involve carbon.
(ii) Look at diagram - test tube A has enzyme in boiling water
test tube B has acid in boiling water.

18. (a) Write in words first
  copper(II) oxide + hydrogen ---> copper + water
Now try symbols
  CuO + ---> +

(b) What colour is copper(II) oxide in the first place? Tells you on the diagram. What colour would copper be ?
(c) Comparing calcium and copper - open page 7.
Which is the most reactive?

19. (a) Mark arrow on diagram on wire. Which electrode has electrons leaving it. You need to look at the information below.
(b) What does made by the cell? Electricity
How is electricity travel in solutions ?
(c) What is not present in sugar.
May help with previous question.
Sugar is a carbohydrate - what type of bonding ?
(d) (i) Look in data book for its position. Number 78
(ii) What gases are produced in car exhausts?
Why would you want to convert them?

20. (a) A salt is formed- products on right hand side – 50% chance
(b) Copy out equation and underline the chemicals you are asked about (hydrogen) and told about (aluminium)

  2Al + 3H2SO4 -----> Al2(SO4)3 + 3H2
step 2 - how many moles of each
  2 moles of Al -----> 3 moles of H2
step 3 - mass of each side
  2 x 27 -----> 3 x 6
54 -----> 18
  So 54g of aluminium produces 18g of hydrogen
Therefore 1g ----->  18  =

Therefore 1.35g ---->

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