National Chemistry

2002 Credit Almost the answers

1. (a) What are the elements required by plants ? P, K, N
(b) bases will neutralise acids. What type of compounds react with acids?
carbonates, oxides and hydroxides

2.(a) What type of bonding is present in sodium chloride ? Ionic
Then what are the conditions for conduction for that bonding ?
Please note B and F have the same conditions AND so do C and E while you are looking for one answer.
(b) molecules (moLOWcules) = low melting point and covalent.
Look for TWO substances with low melting point and the correct conditions for conductivity for covalent
Please note B and F have the same conditions AND so do C and E and you are looking for two answers !

3. (a) Identify which are metals to possibly be X.
Put the charge for each ion in the box - ie +, 2-, 2+, Si4+ !, -, +
From the formula XY2 what charge do you want on the metal X and what charge on the element Y.
If you pick box A then box F would also be true - cannot have both.
(b) What is the formula for methane ? CH4 What element makes the same number of bonds as the Carbon and Hydrogen?
Molecule - just non-metals

4. Write the molecular formula in each box
C4H10; C4H8; C4H8; C4H8; C3H6; C4H10
(a) What type of structure is required to decolourise bromine water - must appear in TWO boxes.
(b) Same molecular formula but different structure. Match up the molecular formula. D is C4H8 but so is B and C but you have to pick only one answer.
Oh! What is those last words of the question? 'belongs to s different homologous series' - so totally different structure.

5.(a) What are the charges on protons (+), electrons (-) and neutrons (neutral).
Remember definition of why an atom is neutral. p=e
Use protons and electrons to work out charge on each particle.
(b) Remember definition of isotope. Same number of protons but different number of neutrons.

6. In the nucleide notation given what does number 6 represent ? Atomic number = number of protons
How is number 14 calculated ? protons + neutrons = mass number
  6 + ? = 14
7. (a) Usually only talk about a reaction not occurring if there is an unreactive metal involved. eg Cu, Ag, Au
(b) For a reaction to form water Hydrogen and oxygen must be present in the reaction - so bomb out E.
D has water as reactant so will not be making it.
What other reactions make water ? eg combustion burning of a fuel, neutralisation of an acid

8. (a) Combustion is burning. What gas do things burn in ? It must be there as a reactant in at least two places.
(b) TWO answers
Rusting is oxidation of iron. So B or F look likely to be involved. Is one oxidation ?
What else occurs during rusting ? reduction of something.

9. TWO answers
Electron arrangement of fluorine is 2,7
Decide if each statement is true or false - in any order.
A. is 2,7 stable ?
B. if 2,7 loses an electron it becomes 2,8
C. Will fluorine be -ve 1 ? see page 7
D. what is oxygen electron arrangement ?
E. what is chlorine electron arrangement ?
F. what is iodine electron arrangement ?

part 2

10. You should know two process associated with refining. Which makes ethene ? Think about its formula. (see question 16)
(b) (i) Look at the polymer structure and copy out what repeats itself.
(ii) look at the polymer structure. What could be produced by burning these elements ? Must contain H or Cl or C

11. (The diagram tells you that starch is heated with hydrochloric acid. The result is then tested with Benedict's solution which turns red. Notice in part (ii) you are told that Ailsa thought that Glucose had been formed.
a) (i) What reaction changes starch to glucose?
(ii) You know another two.
(iii) The only change to the pictured experiment is that amylase is used instead of hydrochloric acid. The questions suggests that it is a surprise that this did not produce the same result. For some reason the amylase id not work.
Where does amylase come from ? saliva
(b) Carbohydrates have 6 or 12 carbons.

12. (a) (i) Do not change any of the formulae.
  TICl4 + H2O -----> TiO2 + HCl
  HCl
  HCl
  HCl

  Now need 4 H on left hand side

(ii) Liquid at room temperature suggests 'low' melting point. Suggest molecule so bonding is ?
(b) Only 1 x Ti in TiO2 (mass of TiO2 is (1 x Ti)+(2 x O)

  48 in 80 x 100 to get percentage

(13(a) Remember spectator ions are like pupils - they do nothing! So score NO3- which appears on both sides then copy out accurately.
(b) One of the reactants (there are three) must be being oxidised. Look on page 7. Ie Cu or Ag+ (NO3- is not on page 7). So must be
  Cu ---> or Ag+ --->

Oxidation goes opposite way. Oxidation is loass (OIL)

 (c) (i) The labels needed are mentioned in the description of the experiment on the first line. 'copper displaces silver from silver nitrate' Three chemical three labels
(ii) Sodium carbonate must cause a problem. dealing with ions so try page
5. Does carbonate react with anything else in the beakers.

14. (a) Add something to the diagram to measure the volume of gas given off. remember in diagrams - nothing open to the air and if liquid present draw it in. It also needs to measure the volume given off so needs a scale.
(b) (b) label both axes; put on the scale; make sure over half the graph paper is used; make sure it is a line graph.

(c) Read it off of your graph - be accurate.
(d) formula for sodium carbonate - use sodium ion (Na+) and carbonate ion (CO32-). Keep the charges in.

15. (a) mercury is unreactive while magnesium is the most reactive of the three.
Which method is the simplest ?
Lead must be the middle description - not heat alone but not need electricity.
(b) What large hot thing is iron produced in ?
(c) step 1: copy out equation
Fe2O3 + 3CO -----> 2Fe + 3CO2

  step 2: underline what chemicals the question is interested in
  Fe2O3 -----> 2Fe
  step 3: write number of moles
  1 mole of Fe2O3 -----> 2 moles of Fe
  step 4: calculate mass of these moles
  (2 x Fe)+(3 x O) -----> (2 x Fe)
  (2 x 56)+(3 x 16) -----> (2 x 56)
160 -----> 112
  thus 160g iron oxide produces 112g iron
  step 5: units are not g!
thus 160tonnes iron oxide produces 112tonnes iron
  step 6: calculate how much 1600 tonnes would produce

16. (a) first two lines tells you that glucose undergoes fermentation to produce alcohol plus a gas. The formula of glucose is C6H12O6 - what possible gases could come from this compound. Since no nitrogen it cannot be NO2.
(b) 15% alcohol concentration stops it - must prevent something happening
(c) (i) The main reactant is an alkene; unsaturated; C=C double bond
(ii) look at the example given. What change occurs when the product is formed?
The double bond beaks; one carbon of the double bond gets another H; the other carbon of the double bond gets a OH.
Do the same to the molecule in the question. make the double bond a single and put the H and OH onto the carbons.

17. (a) Write the molecular formula for each molecule in the boxes. Just need the right hand side molecules as these are the aldehydes and ketones - so C2H4O; C3H6O; C3H6O and C4H8O -
general formul should be of the kind CnHn
(b) Look at the structures of the alcohol and what is formed. First two make aldehyde and second two make ketone. Where is the OH part of the molecule ?
c) Two metals suggest some kind of comparison.
Copper oxide is reduced to copper metal but, the question suggests, that aluminium oxide cannot be reduced to aluminium.

18. (a) What is the advantage of using air and water rather than other chemicals ?
(b) What is the formula of ammonia ? NH3
What elements are needed ? nitrogen and hydrogen ? Which from the air ?
(c) Acid + Alkali makes a salt. The acid is phosphoric acid.
Use page 4 to get the second name of the salt.
First name of salt comes from the ammonia plant
(d) (i) Pressure is the X axis but careful the question is about temperature and yield.
The yield increase/decreases/stays the same as temperature increases
(ii) Might help with part (b)
Can something from the graph help - temperature

19. burette, numbers, titre - it is a titration calculation
(a)(i) The volumes are - do not use the rough value - 20.0 and 20.2
(ii) Use this average volume to calculate the number of moles.
 
  number of moles = volume and concentration

  You have the volume - guess 20.7 if you did not answer part (a).
  Change it to litres
  Find the concentration on the diagram.
Multiply together.

(b) You know the number of moles from part (ii) - (if not guess 5)
Questions states 1 mole of ethanoic acid reacts with 1 mole of sodium hydroxide.
Which means 1 mole of sodium hydroxide reacts with 1 mole of ethanoic acid.
If you have guessed 5 mole of sodium hydroxide.
How many mole of acid ?

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