OCR GCSE Chemistry C4,5,6 UNOFFICIAL MARKSCHEME

I think C5 concentration is 0.18 mol/dm^3 because 1 mole of HCl neutralises 1 mole of the potassium hydroxide as you could tell from the symbol equation therefore if the number of moles of HCl was 0.009 it means the number of moles of Potassium Hydroxide is also 0.009 and there was 50cm^3 of potassium hydroxide so 50/1000 = 0.05 and concentration = number of moles over volume therefore 0.009/0.05 = 0.18 mol/dm^3.

I also think "What is meant by relative atomic mass?" the answer is The average mass of an atom of the element compared to 1/12th of the mass of an atom of carbon-12.

I think C5 concentration is 0.18 mol/dm^3 because 1 mole of HCl neutralises 1 mole of the potassium hydroxide as you could tell from the symbol equation therefore if the number of moles of HCl was 0.009 it means the number of moles of Potassium Hydroxide is also 0.009 and there was 50cm^3 of potassium hydroxide so 50/1000 = 0.05 and concentration = number of moles over volume therefore 0.009/0.05 = 0.18 mol/dm^3.

I also think "What is meant by relative atomic mass?" the answer is The average mass of an atom of the element compared to 1/12th of the mass of an atom of carbon-12.

also it was 0.009/ 0.02 as the volume was 20cm3 so the answer was 0.045moldm-3

oh there was that hard balancing equations one
calcium carbonate added to hydrochloric aicd?

The volume of the acid was 20cm^3, it wanted the concentration of the alkali.

If I forget anything, write in the comments

C4
Question about ions and atoms
- Mg+ (1)
- MgFl2 (1)

Why and how do Lithium atoms form ions
-It loses electrons to become stable (1)
-It loses one electron: Li- -> Li + e- (1)

Draw Na20
-dot and cross diagram with 2- charge on Oxygen atom and +1 charge on both sodium atoms

Table to fill in with Protons, Neutrons (2)
Protons: 1, +1 (1)
Neutrons: 1, 0

Why is the atom neutral?
-It has the same number of protons as electrons (1)

Size of Atom- C
forgot the q after that

Predict the properties of ammonia (4)
-Gas at room temperature
-Doesn't conduct electricity
-Low melting and boiling point due to weak IM bonds

Balancing:
CaCO3 + 2HCl -> H20 + CaCl2 + CO2 (2)

6 marker on Halogens and reactivity
-Reaction Cl2 + 2NaBr -> 2NaCl + 2Br
-Order: Z (Fluorine) ,Cl,Y (Bromine),X (Iodine) (Dont have to name them)
Explanation: Z displaced 3 solutions, Cl displaced 2, Y displaced 1 and X displaced 0

C5
Titration:
22 (1)
20(1)

30cm3 = 0.03 dm3
0.03*0.3= 0.009 mol (1)

Concentration is 0.45moldm-3 (2)

Percentage of Magnesium: 28.7% (not sure) (1)

Explain what is relative atomic mass:
-Number of protons and neutrons

mass of hydrogen: 0.004g (2)
-48cm3 = 0.048dm3
0.048/24= 0.002mol
0.002*2=0.004g

Contact Process question (screwed this one up)

Under what conditions and why the reaction is at equilibrium:
-closed system (2)
-forward reaction same as backward reaction (1)

Position of equilibrium when Oxygen is added:
-Shifts to the right (1)

Conditions of Contact Process:
-Vanadium Pentoxide (V2O5) Catalyst (1)
-High temp: 450C (1)

Conclusions about concentration of hydrogen:
Both right i think (2)

6 marker on preparing insoluble salts
Equation: Pb2+ 2I- -> PbI2
Method:
Precipitate-add lead nitrate to distilled water and do the same with the other and tip both solutions to a small beaker
Filter-put a piece of folded filter paper into funnel and stick funnel into conical flask and then swill out the beaker with more distilled water
Dry- Rinse contents with distilled water to wash soluble salts away, leave it to dry
C6
Rusting of iron equation:
-Water + Oxygen + Water -> Hydrated Iron (III) Oxide (1)

Galvanising question:
-Done with zinc and acts as sacrificial protection so it will lose electrons in preference to iron (1)
-Acts as a barrier to water and air (1)

Redox reaction: oilrig cheeky mention
-Reduction happens to Iron as it gains electrons (1)
-Magnesium is oxidised as it loses electrons (1)
Redox since both happening at same time

Alternative to ozone:
-Alkane (1)

In terms of electons, how is Chlorine and Carbon bonds split:
-Covalent bond is broken evenly where both chlorine and carbon get one of the electrons (making them both highly reactive as radicals) (2)

Why did attitudes to CFCs change (2)
-They found out Chlorine from CFCs could destroy ozone
-They found out that CFCs cause the depletion of Ozone Layer

Energy Level Diagram
-Exothermic as energy is released, there is less energy in the product (1)

Fuel Cell Question:
-O2 + 4H+ + 4e- -> 2H20 (2)

Which solution is temporary:
-A as it had hardness before boiling and none after (2)

What causes permanent hardness in water
-Calcium Sulfate (1)

6 marker on Detergents:
-Peter was right as it had excellent whiteness and something else and had very good prevention of colour fading

-Detergents have a hydrophilic head and a hydrophobic tail.
-Grease has weak IM bonds in between and so does the detergent
-The detergent forms stron IM bonds with grease due to hydrophobic tail
-Hence the detergent surrounds the grease and attaches to water
-Lifting the grease off of the clothes

Dry Cleaning:
-Solvent used is not water (1)
-Water can damage delicate linen (1)

SECTION D
idk

Hi there, I have a query about the first 6 marker. I got the opposite way round from your answers, my idea being:

If X has no reaction with none of the three it must therefore be more reactive as the other solutions don't displace it?

I see your way of thinking, just hoping somebody can floor my thinking????

Ahhh so I must have got the displacement the wrong way round... I can still hope for a few marks though, right? xD

The answer after the size of the atom question was 6 (I think)

For the direction of the equilibrium I'm pretty sure it moves to the left because only pressure can move it to the right..?