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

Ka 7.21x10-3
22.65cm3
-0.013V and 303K
-0.8V
1.47%

isn't the % uncertainty ＝0.005/0.685 something

7.1*10^-3 for the KA?

7.21*10∧-3

isn't the % uncertainty ＝0.005/0.685 something

I don’t think it was -0.8V it was positive cause 0.8+0.33=1.13

i got 0.73%

it was oxidation so flip the sign?

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

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?