AQA A2 CHEM4 & CHEM5 June 2015 [official discussion thread]

Reply 3980

p208134

2

Original post by RThornton

I got -363.5?

I got that couldn't remember 100%

Reply 3981

chem@uni

9

0.383?

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Reply 3982

p208134

2

Original post by Thomas_Zhou

0.38moldm^3 concentration anyone? Please.

I got 0.072 the only reason was you x10 didn't you to go from 25cm3 to get to 250Cm3 but I thought it meant the original X Fe value and x2 to go from 25cm3 to get to 50cm3 Idk if i was correct and am regretting it now :frown:

Reply 3983

_Caz_

10

Original post by chem@uni

0.383?

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Was this for the five mark calculation?I got this too if so.

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Reply 3984

Thomas_Zhou

1

Original post by p208134

I got 0.072 the only reason was you x10 didn't you to go from 25cm3 to get to 250Cm3 but I thought it meant the original X Fe value and x2 to go from 25cm3 to get to 50cm3 Idk if i was correct and am regretting it now :frown:

I think I times the concentration i calculated and times it by 250cm3 to get the number of moles of Iron Sulfate then used that value and divide by 50cm^3 to find the original concentration of X if that makes any sense

Reply 3985

ekk123

11

What was the weakest oxidising agent guys?

Reply 3986

Protoxylic

14

The 50cm^3 added sulfuric acid for the titration was an irrelevant piece of information, it wasn't needed for the calculation to find the concentration of Fe(III) in X.

Reply 3987

Protoxylic

14

Original post by ekk123

What was the weakest oxidising agent guys?

Fe(II) iirc

Reply 3988

THEMathlete

12

Well that was... Okay

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Reply 3989

RThornton

4

Original post by ekk123

What was the weakest oxidising agent guys?

Fe2+

Reply 3990

aalex.. ~~~

6

Guys how to do Cr(OH)3(H2O)3 + HCL? I have no idea

Reply 3991

anngreg

1

Was the indicator colour change colourless to purple? and what did people put for Chromium (iii) hydroxide with HCl?

Reply 3992

than4711

1

Original post by Protoxylic

The 50cm^3 added sulfuric acid for the titration was an irrelevant piece of information, it wasn't needed for the calculation to find the concentration of Fe(III) in X.

true that it doest affect, :tongue:

but H2SO4 is added to make sure MnO4- form Mn2+, not MnO2 (i think)

Reply 3993

THEMathlete

12

Original post by chem@uni

0.383?

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I hope ur right

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Reply 3994

aalex.. ~~~

6

Original post by anngreg

Was the indicator colour change colourless to purple? and what did people put for Chromium (iii) hydroxide with HCl?

I put pink ;( and due to excess MnO4-

Reply 3995

p208134

2

Original post by Protoxylic

The 50cm^3 added sulfuric acid for the titration was an irrelevant piece of information, it wasn't needed for the calculation to find the concentration of Fe(III) in X.

Why would they include it oh well 12 marks lost than

Reply 3996

rohan9777

1

What do you reckon grade boundaries will be? about 86-87 for an a*?

Reply 3997

hukdealz

10

Original post by RThornton

Fe2+

no, it was F2, unlucky!

Reply 3998

than4711

1

Here are my answers for the caculations, i managed to put in my graphic calculator:
-363.5
-155
-244
206
216
954
976
250K( for SO2 MP)
0.383

(edited 8 years ago)

Reply 3999

anngreg

1

Original post by Protoxylic

The 50cm^3 added sulfuric acid for the titration was an irrelevant piece of information, it wasn't needed for the calculation to find the concentration of Fe(III) in X.