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A-Level OCR Chemistry B (Salters) 2017

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Reply 60

Matteus3

I put impurities/recrystallise ???

Reply 61

Logic4Life

Original post by GenuineHpLaptop

what did u get for the last queation, why strontium is less soluble, shouldnt it be more cause lower bond enthalpy?

and for the 6m on crystals what were the inaccuracies

Magnesium has a higher charge density so its better at attracting water molecules giving it a greater enthalpy of hydration?

Reply 62

Logic4Life

Does it matter how many significant figures we left our answers to??? It didn't indicate in the question so I used 2 sig fig throughout...

Reply 63

LaurenLovesMaths

Does it matter if you squeeze some of your answer just under the dotted lines they gave for it? I did that for quite a few questions eeek

Reply 64

Logic4Life

Original post by faturbansloth

What did everyone put for the last 6 marker?I wrote about measuring mass of precipitate, the finding the moles of the precipitate and therefore the moles of MgSo4.xH2O. Then using the mass to find the molecular mass of it, minusing the molecular mass of MgSO4 and dividing by 18 to find the value of X.

Yeah I got that too but i was stuck on finding improvements :/

Reply 65

BluntBluster

Original post by LaurenLovesMaths

Does it matter if you squeeze some of your answer just under the dotted lines they gave for it? I did that for quite a few questions eeek

I should hope so, the people marking these are, well, people. Pretty sure they can just read a little bit under the lines. I made a meal of my paper in terms of writing, though the examiners wouldn't be able to read it so just kept crossing stuff out and rewriting looooooooooool i hate nerves

Reply 66

BluntBluster

Original post by 10CogginsK

what did people get for the hess cycle calculation? I got -100kjmol-1

Arrows on the cycle go downwards I'm sure, I did what you did but then clocked

Reply 67

faturbansloth

Original post by Logic4Life

Yeah I got that too but i was stuck on finding improvements :/

I put the usual, make sure completely dissolved, standard temp and pressure etc

Reply 68

BluntBluster

0.15 Tonnes
Wavelength = -3.96x10^-7m
Kc = 0.329
Ratio = 0.80
Hess Cycle = -61.8
MgS04 LE = -2937

Reply 69

Ed5

Original post by faturbansloth

I put the usual, make sure completely dissolved, standard temp and pressure etc

I put make sure completely dissolved + dry the solid after it precipitates out

Reply 70

LaurenLovesMaths

Original post by 10CogginsK

what did people get for the hess cycle calculation? I got -100kjmol-1

Yeah I got -99.9

Reply 71

Rager6amer

Original post by Logic4Life

Does it matter how many significant figures we left our answers to??? It didn't indicate in the question so I used 2 sig fig throughout...

There was 1 question i think that asked for them to an appropriate number of sig figs, but you make your answer as accurate as your least accurate piece of data given. 2 SF should be fine for most/all questions, so you should't be penalised :smile:

Reply 72

Dandie12

What did everyone put for the test for the ions

Reply 73

Logic4Life

Original post by BluntBluster

0.15 Tonnes
Wavelength = -3.96x10^-7m
Kc = 0.329
Ratio = 0.80
Hess Cycle = -61.8
MgS04 LE = -2937

I got the same answers apart from the wavelength one.

Reply 74

Logic4Life

Original post by Dandie12

What did everyone put for the test for the ions

NaOH was definitely one cant remember other 2

Reply 75

Dandie12

Original post by Logic4Life

NaOH was definitely one cant remember other 2

I used NaOH A Sulphate and an iodide

Reply 76

faturbansloth

Original post by Ed5

I put make sure completely dissolved + dry the solid after it precipitates out

Yes I also put dry the precipitate out, hope we are right!

Reply 77

BluntBluster

Original post by Logic4Life

I got the same answers apart from the wavelength one.

Most people I know got that so idk

Reply 78

Logic4Life

First 6 marker was just emission and absorption spectras?

Reply 79

Historygcse

For the first six marker, it was just about electron being excited then returning back to lower energy levels etc right? (the usual for this sort of question)? Then at the end- use known emission spectra of strontium and compare?