OCR Chemistry AS Depth Thursday 23rd 2019 Unofficial Markscheme

1) weighted mean mass of an atom compared to the mass of 1/12 a carbon 12 atom
2) something like 86?
3) some volumes were 60, 35.8 (or 38.5)? cm3?

Sr + 2H2O --> Sr(OH)2 + H2
If you use calcium (less reactive), it's less vigorous (it'll take more time for the metal to dissolve and more times for the bubbling assuming same mass used) but also pH will be less (as you go down group 2, they get more alkaline).

For the hydrolysis, you use a timer and see how long it takes for a precipitate to form. C-I bond enthalpy is lower so reacts faster.

For catalyst, reduces activation energy by providing alternative reaction pathway so more particles have energy >= activation increasing rate.

As the reaction progresses, rate decreases as rectants are used up (conc goes down) so the number of unreacted particles colliding decreases per unit time ==>> rate goes down over time.

With the new graph, it hits the same volume at the end (as number of moles is the same) but it's done faster.



First 6 marker:
I found the mass needed, 25.63g or something. So I said get this mass, weighing boat, 100cm3 beaker and stirr, add distilled water, put into volumetric flask (through funnel), rise the beaker and transfer the rinse and then add distilled water until bottom of miniscus is at 250 then invert for uniform concentration then you've got it?

Second 6 marker:
Mass 8.16g? So first you remove water by getting organic and aqueous layer, separating funnel, invert, allow to settle, add water, the layer that expands is water and water is denser than both so in bottom then remove the water onto a flask and same for conical flask for organic layer and then you have both the organic layer and aqueous then you wanna separate hexan-1-ol and the alkene by redistilling it and colleting off the liquid hex-1-ene.

If you use hexan-2-ol, you reduce yield as you also make hexan-2-ene.


Metallic bonding - strong electrostatic attraction between sea of delocalised electrons and positive metal cations. A high temperature is needed to provide sufficient energy to overcome these strong electrostatic forces, hence high elting point. These delocalised electrons can move and conduct.

Polymer - I said fertiliser? Is this even a mark?

For drawing, I did 2 repeat units for it.

Nickel catalyst needed, solution turns from orange to colorless.

For drawing the 3, one was just an alkane, one had a H at the end and chlorine at penultimate one (for major product) and one had 2 bromines.


X=5.8
He did it many times to heat to constant mass and ensure no water of crystallisation left.

Modifications:
1) more accurate mass balance to more dp
2) use larger mass.

No fam

Could you tell me all the topics if possible for the exam as my exam is tomorrow

I’m willing to pay for it if you have access to it

I know this I late but can someone explain to me how they got 8.16 for the grams (I haven’t done the paper yet ) but what Info was given on that question ? Like where did 0.625 come from

o.625 came as it says in the question that the theoretical yield or something is 62.5 so you divide by 100 because in percentage yield you times by a hundred in the end. So you get the moles divide by 0.625 then times by the mr of the thing being made (which is 102) to get 8.16

Oh okok cool , so they gave that info so that should be okay 👌, one last question I’ve been reading through this and I’ve done so much reading up on it , about the question which it asked for water of crystallisation and so many people got 5.8 ? Is that even possible , because I thought you were supposed to round to whole numbers all the time , so did it specifically ask for a decimal ?

What did you get for X in SrCl2 x H2O? I got 5.8 when not rounding any other calcs but 5.9 when rounding. I went with 5.8 in the end. Overall I felt like it was a good paper, the 6 markers were nice too

hey could you send me the paper/questions