AQA A-level Chemistry 7405 - Paper 3 - 19th June 2019 unofficial mark scheme Watch

CeliaaaWuuu
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AQA A-level Chemistry 7405 - Paper 3 - 19th June 2019

this is my multiple choice answer

CADCC
BAABB
AADAB
ACAAB
CDADC
DADDD
Last edited by CeliaaaWuuu; 4 weeks ago
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Khushi.S
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7.1*10^-3 for the KA?
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melonmelon
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Ka 7.21x10-3
22.65cm3
-0.013V and 303K
-0.8V
1.47%
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CeliaaaWuuu
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isn't the % uncertainty =0.005/0.685 something
(Original post by melonmelon)
Ka 7.21x10-3
22.65cm3
-0.013V and 303K
-0.8V
1.47%
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CeliaaaWuuu
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i got 0.73%
(Original post by CeliaaaWuuu)
isn't the % uncertainty =0.005/0.685 something
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KVJ
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This is quick lol
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CeliaaaWuuu
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7.21*10∧-3
(Original post by Khushi.S)
7.1*10^-3 for the KA?
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0rg4n1c
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you had to multiply 0.005 by 2 since the weighing involved 2 readings
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mpatel12
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It was once used to measure mass of container and once to measure mass of container and solid. Uncertainty will be ×2
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Evil Homer
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How did it go today guys?
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Khushi.S
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(Original post by CeliaaaWuuu)
7.21*10∧-3
Sorry yeah, I missed out the two
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zixd
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I don’t think it was -0.8V it was positive cause 0.8+0.33=1.13




(Original post by CeliaaaWuuu)
isn't the % uncertainty =0.005/0.685 something
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melonmelon
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(Original post by zixd)
I don’t think it was -0.8V it was positive cause 0.8+0.33=1.13



it was oxidation so flip the sign?
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Tonyaefv
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(Original post by CeliaaaWuuu)
i got 0.73%
need to times by 2
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zixd
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(Original post by melonmelon)
it was oxidation so flip the sign?
Ahhhh ffs didn’t even think of that
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melonmelon
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S2O3 2- + 2H+  S + So2 + h20
so2 is acidic
SO2 + H2O --> H2SO3
Sodium thiosulfate and hcl, water bath, range of temperatures, conical flask on top of a black cross stopwatch, time taken for cross to disappear, rate is 1/time. Plot 1/time against temperature, exponential shape due to Arhenius equation

H2SO4  H+ + HSO4-
HSO4- <-> H+ +so4 2-
Ka is 7.21x10^-3
Increased conc of so4 2-, so equilibrium shifts left, H+ decreases and ph Increases

Salt bridge
Allows movement of ions
Platinum
C; HCL/1 moldm3
D: hydrogen gas at 100kPa
E: solution of fe2+ and fe 3+ at 1 moldm3
2Fe3+ + H2 --> 2Fe2+ + 2H+

-0.013V (gradient)
303K
-0.80V

Nucleophilic addition
Racemic mixture
Planar C=O, Equal probability of nucleophilic attack from above and below the plane, racemate formed
Draw optical isomers of 2hydroxypropanenitrile (mirror images in 3D)
C.h2s04/ 600K
3 repeating units with trailing bonds

Fe + h2so4  feso4 +h2
MnO4-(aq) + 8H+(aq) + 5Fe2+ (aq) Mn2+ (aq) + 4H2O (l) + 5Fe3+ (aq)
Colourless to pale pink/purple
22.65 cm3
1.47% as two readings

Some multiple choice
-1139
+0.78V
Benzoic acid
Last edited by melonmelon; 4 weeks ago
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TomSR
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ignore this
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Khushi.S
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(Original post by melonmelon)
S2O3 2- + 2H+  S + So2 + h20
Sodium thiosulfate and hcl, water bath, range of temperatures, conical flask on top of a black cross stopwatch, time taken for cross to disappear, rate is 1/time. Plot 1/time against temperature, exponential shape due to Arhenius equation

H2SO4  H+ + HSO4-
HSO4- <-> H+ +so4 2-
Ka is 7.21x10^-3
Increased conc of so4 2-, so equilibrium shifts left, H+ decreases and ph Increases

Salt bridge
Allows movement of ions
Platinum
C; HCL/1 moldm3
D: hydrogen gas at 100kPa
E: solution of fe2+ and fe 3+ at 1 moldm3
-0.80V

Nucleophilic addition
Racemic mixture
Planar C=O, Equal probability of nucleophilic attack from above and below the plane, racemate formed
Draw optical isomers of 2hydroxypropanenitrile (mirror images in 3D)
C.h2s04/ 600K
3 repeating units with trailing bonds

Fe + h2so4  feso4 +h2
MnO4-(aq) + 8H+(aq) + 5Fe2+ (aq) Mn2+ (aq) + 4H2O (l) + 5Fe3+ (aq)
Colourless to pale pink/purple
22.65 cm3
1.47% as two readings

Some multiple choice
-1139
+0.78V
Benzoic acid
Yes I got all of these
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haf4321
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Gradient -0.013V
E value of Zn was -0.8V
Uncertainty was like 0.73% cant remember exactly
Mean titre 22.65cm3
What was the answer to which compound is the best drying agent and which compound can be recrystallised?
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melonmelon
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(Original post by haf4321)
Gradient -0.013V
E value of Zn was -0.8V
Uncertainty was like 0.73% cant remember exactly
Mean titre 22.65cm3
What was the answer to which compound is the best drying agent and which compound can be recrystallised?
calcium sulfate and benzoic acid
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