Edexcel Chemistry IGCSE 1C Unofficial Mark Scheme 19th May 2016

Why did hydrogen have a low melting point?

What about that question on why solution Y gave a lower temperarure and why the burrete had to be cleaned with water and solution y .

I put that solution Y was more dilute than solution x

Wasn't too sure about the cleaning of the burette but I put:

Water - To wash out any remaining solution x
Solution Y - To react with the water, so only solution Y was present.

For question 3f.) the first part of the question was asking which one shows a noble gas. The answer was - atom with 8 electrons in outer shell. That should complete all 5 parts of 3f giving 5 marks in total I think.

There were 6 parts to it, it was out of 6 marks.

oops...what was the 6th one? There's only 4 on the unofficial mark scheme

Could you explain the first answer? (solution Y was more dilute than solution x)
Would "because Y had a higher initial temperaure" be correct?

Tell me the questions which I'm missing out - I'll add them in. Please try your best to remember the rough question number.

1.a)
Condensation. (1)

1.b)
Energy: average ke of particles decreases.
Arrangement: the intermolecular spaces decrease (as some intermolecular
forces between particles start to form).
Movement: particles in liquids slide over each other. (3)

2.a)
Filtration. (1)

2.b)
Arrow drawn into solvent inside beaker.
Arrow drawn onto chromatography paper.
Arrow drawn onto the line on the chromatography paper. (3)

2.c)
There are for 4 dyes present in the substance as the original substance
dissolved into the solvent and 4 dyes were drawn up. (1)

3.a)
Hydrogen molecule bonding - two circles that cross over each other and at the
point of intersection there is a cross and a dot. The circles both have letters H
inside of them. (1)

3.b)
Element in the air - argon. (1)

3.c)
Compound present in unpolluted air - H2O (water) or CO2 (carbon dioxide). (1)

3.d)
Isotopes are atoms with specific number of neutrons independent to the number of protons that defines the element. (2)

3.e)
H1 - 1 proton, 0 neutrons, 1 electron.
H2 - 1 proton, 1 neutron, 1 electron.
H3 - 1 proton, 2 neutrons, 1 electron. (3)

3.f)
Atom with 3 protons - the diagram with 3 dots.
Atom in period 3 - the diagram with 15 dots (phosphorous).
Atom with 15 electrons - diagram with 15 dots (phosphorous).
Atom which is stable - diagram with 8 dots in outer shell (Neon).

3.g)
A pair of electrons and nuclei of two atoms. (2)

4.a)
Simple filling in the temperatures - to 1 dp. (4)

4.b)
Max temperature produced by magnesium. (1)

4.c)
Ice used to cool down and condense the water vapour. (1)

4.d)
Products formed - magnesium chloride and hydrogen (gas). (2)

4.e) Magnesium can't be used in the reaction using air as it would oxidise to form magnesium oxide. (1)

4.f)
Increasing volume of acid to 50cm3 - not so great a rise in temperature as increase in volume of acid means that more energy is required for the same rise in temperature. (2)

4.g)
Draw arrow up onto the powder. (1)

5.a)
Copper pile turns black because the oxygen in the air reacts with it in a combustion reaction to form Copper oxide (black solid). (2)

5.b)
The gas is cooled down before it is measured so that its volume can be recorded at rtp (as the original volume had been measured in these conditions). Heated gases = expansion of volume. (1)

5.c)
Why didn't the small heap of copper turn black - because all of the oxygen in the air had been used up in the previous reaction hence no combustion reaction to oxidise copper. (1)

5.d)
Percentage of oxygen - 16.6 (recurring) or 16.7%. (2)

5.e)
Hydrogen has a low m + b pt. as it is a simple molecular compound hence has weak intermolecular forces which don't require a lot of energy to break. (2)

6.a)
In order of reactivity - Q, R, S, P. (4)

6.b)
Graph - draw straight lines of best fit, both lines must intersect. (4)

6.c)
Volume used - 12.5 cm3. (1)

6.d)
10 degrees celcius. (1)

7.a)
Test for presence of water - add to anhydrous copper (II) sulphate, turns white to blue.
OR add to anhydrous cobalt (II) chloride paper, turns blue to pink. (2)

7.b)
Test for purity - physical boiling point test - boils at 100 degrees celsius. (1)

9.a)
I2 + Cl2 = 2ICl. (1)

9.b)
Two features of equilibrium - rate of forward reaction = rate of reverse reaction and concentration of
products and reactants are equal. (2)

9.c)
The reverse reaction was endothermic because if the forward reaction is exothermic, increasing the temperature decreases the amount of product being formed hence equilibrium shifts to the left where ICl is formed which is brown. (2)

9.d)
Test for chloride ions - add nitric acid and silver nitrate, a white precipitate of silver chloride will form. (2)

10.a)
Enthalpy change. (1)

10.b)
19740 J - something around that. (2)

10.c)
Exothermic reaction - transfer of energy from system to surroundings. (1)

11.a)
Propane. (1)

11.b)
C4H10. (1)

11.c)
W, X, Y. (1)

11.d)
Empirical formula for Y - CH2. (1)

11.d)
A hydrocarbon with a double carbon = carbon covalent bond.
A hydrocarbon is a organic compound made of hydrogen and carbon only. (3)

11.e)
Displayed formula should have only 1 Br atom in it. (1)

11.f)
Condition required - UV light. (1)

12.a)
Carbon soot was formed in the incomplete combustion due to insufficient oxygen. (1)

12.b)
Reason why this affected result - fuel doesn't react fully with air due to insufficient oxygen in incomplete combustion hence not as much energy release. (1)

12.c)
Other loss of energy - heat energy lost to surroundings, hence not all transferred to water. (1)

13.a)
Reason for cotton wool - prevent acid from spitting out during reaction. (1)

14.a)Fill in the boxes for number of moles in the thermal decomposition. (4)

14.b)
Third equation is correct because 2 mole of the original substance forms 1 mole of the product and the table values were 0.08 moles and 0.04 moles. (2)

15.a)
Formula of titanium something must equal to that of the question. (2)

15.b)
Structure of titanium - giant metallic, layers of +ve ions surrounded by a sea of delocalised electrons. (2)

15.c)
Titanium is conductive as free delocalised electrons don't belong to specific ion hence can quickly transfer charge form -ve to +ve terminal in circuit. (1)

16.a)
Draw graph line - steeper and levels off first but at same level. (2)

16.c)
Increase in concentration = increase in particles per unit volume, hence increase in no. of collisions per unit time hence increase in no. of successful collisions per unit time, hence increase in rate of reaction. (3)

Where are the other 20 marks????

I thought that both solution X and Y were HCL, and the only reason I could think of that would result in one reaction having a higher enthalpy change was that one of the solutions was more concentrated than the other, which would result in a more vigorous reaction.
Idk its technically correct so maybe

I thought that both solution X and Y were HCL, and the only reason I could think of that would result in one reaction having a higher enthalpy change was that one of the solutions was more concentrated than the other, which would result in a more vigorous reaction.
Idk its technically correct so maybe