A LEVEL CHEMISTRY: ALL PAPER 1
QUESTIONS AND ANSWERS 100%
ACCURATE
0 4 . 5 A 6.01 g sample of salicylic acid (Mr = 138.0) is reacted with 10.0 cm3 of ethanoic anhydride (Mr =
102.0). In the reaction the yield of aspirin is 84.1%
The density of ethanoic anhydride is 1.08 g cm-3
Show by calculation which reagent is in excess. Calculate the mass, in g, of aspirin (Mr = 180.0)
produced. [5 marks] - ANS-1) find which is in excess:
moles of salicylic acid= 6.01/138= 0.0436
mass of ethanoic anhydride= 1.08 x 10= 10.8g
moles= 10.8/102= 0.106
so ethanoic anhydride is in excess
2) if yield of asprin was 100% moles of asprin would be:
0.436 so mass= 0.436 x 180= 7.848g
3) find the mass of 84.1%:
7.848 x (84.1/100)= 6.59g
This question is about citric acid, a hydrated tricarboxylic acid. Its formula can be represented as
H3Y.𝑥H2O
0 8 . 1 A 1.50 g sample of H3Y.𝑥H2O contains 0.913 g of oxygen by mass.
The sample burns completely in air to form 1.89 g of CO2 and 0.643 g of H2O
Show that the empirical formula of citric acid is C3H5O4 [5 marks] - ANS-1) find the moles of O2:
0.913/16= 0.057
2) find the moles of CO2:
1.89/44= 0.04295
3) therefor the moles of C are 0.04295
,4) find the moles of H2O:
0.643/18= 0.0357
5) therefore the moles of H are 2 x 0.0357= 0.0714
6) simplify the ratio by dividing by smallest number:
C= 1, H= 1.66, O= 1.33
7) then multiply up ratio to a whole number:
multiplied by 3= C= 3, H= 5, O= 4
calculate the mass, in g, of hexan-2-ol formed from 11cm3 of hex-1-ene if the yield is 31.0%.
give your answer to 1dp
density of hex-1-ene= 0.678cm3 [4 marks] - ANS-1) calculate the mass of hex-1-ene:
0.678 x 11= 7.458g
2) find the moles of hex-1-ene:
7.458/84= 0.08879
3) find the moles of hexan-2-ol:
it's a 1:1 ratio so moles= 0.08879
4) find 100% yield mass:
0.08879 x 102 = 9.06g
5) find 31% yield mass:
9.06 x (31/100)= 2.8g
this question is about olive oil.
A sample of olive oil is mainly the unsaturated fat Y mixed with a small amount of inert impurity,
Y has an Mr of 880.
The amount of Y is found measuring how much bromine water is decolourised by a sample of oil, using
this method.
- transfer a weighed sample of oil to a 250cm3 volumetric flask and make up to the mark with an inert
organic solvent.
- titrate 25cm3 samples of the olive oil solution with 0.025 mol dm3 Br2
, calculate a suitable mass of olive oil to transfer to the volumetric flask using your answer to 09.1
(7.5x10-4) moles of Br2) and the structure of Y.
assume that olive oil contains 85% of Y by mass.
(structure has 5 double bonded carbons)
[5 marks] - ANS-1) find the ratio of Br2 to Y:
5:1
2) find the moles of Y:
7.5x10-4/5= 1.5x10-4
3) find the moles in 250cm3:
1.5x10-4 x 10= 1.5x10-3
4) find the mass if the yield of Y was 100%:
1.5x10-3 x 880= 1.32g
5) find the mass of olive oil needed:
1.32 x (100/85) = 1.55g
A sample of rhenium is ionised by electron impact in a time of flight mass spectrometer.
A 185Re+ ion with a kinetic energy of 1.153x10-13J travels through a 1.450m flight tube.
The kinetic energy of the ion is given by the equation KE= 1/2mv^2
where
m= mass/ kg
v= speed/ m s-1
KE= kinetic energy/ J
calculate the time, in seconds, for the ion to reach the detector.
The Avogadro constant, L= 6.022x10^23 mol-1
[5 marks] - ANS-1) rearrange equation:
V= √2KE/m
2) find the mass of the ion:
(185/6.022x10^23)/1000 = 3.0721x10-25
3) substitute:
QUESTIONS AND ANSWERS 100%
ACCURATE
0 4 . 5 A 6.01 g sample of salicylic acid (Mr = 138.0) is reacted with 10.0 cm3 of ethanoic anhydride (Mr =
102.0). In the reaction the yield of aspirin is 84.1%
The density of ethanoic anhydride is 1.08 g cm-3
Show by calculation which reagent is in excess. Calculate the mass, in g, of aspirin (Mr = 180.0)
produced. [5 marks] - ANS-1) find which is in excess:
moles of salicylic acid= 6.01/138= 0.0436
mass of ethanoic anhydride= 1.08 x 10= 10.8g
moles= 10.8/102= 0.106
so ethanoic anhydride is in excess
2) if yield of asprin was 100% moles of asprin would be:
0.436 so mass= 0.436 x 180= 7.848g
3) find the mass of 84.1%:
7.848 x (84.1/100)= 6.59g
This question is about citric acid, a hydrated tricarboxylic acid. Its formula can be represented as
H3Y.𝑥H2O
0 8 . 1 A 1.50 g sample of H3Y.𝑥H2O contains 0.913 g of oxygen by mass.
The sample burns completely in air to form 1.89 g of CO2 and 0.643 g of H2O
Show that the empirical formula of citric acid is C3H5O4 [5 marks] - ANS-1) find the moles of O2:
0.913/16= 0.057
2) find the moles of CO2:
1.89/44= 0.04295
3) therefor the moles of C are 0.04295
,4) find the moles of H2O:
0.643/18= 0.0357
5) therefore the moles of H are 2 x 0.0357= 0.0714
6) simplify the ratio by dividing by smallest number:
C= 1, H= 1.66, O= 1.33
7) then multiply up ratio to a whole number:
multiplied by 3= C= 3, H= 5, O= 4
calculate the mass, in g, of hexan-2-ol formed from 11cm3 of hex-1-ene if the yield is 31.0%.
give your answer to 1dp
density of hex-1-ene= 0.678cm3 [4 marks] - ANS-1) calculate the mass of hex-1-ene:
0.678 x 11= 7.458g
2) find the moles of hex-1-ene:
7.458/84= 0.08879
3) find the moles of hexan-2-ol:
it's a 1:1 ratio so moles= 0.08879
4) find 100% yield mass:
0.08879 x 102 = 9.06g
5) find 31% yield mass:
9.06 x (31/100)= 2.8g
this question is about olive oil.
A sample of olive oil is mainly the unsaturated fat Y mixed with a small amount of inert impurity,
Y has an Mr of 880.
The amount of Y is found measuring how much bromine water is decolourised by a sample of oil, using
this method.
- transfer a weighed sample of oil to a 250cm3 volumetric flask and make up to the mark with an inert
organic solvent.
- titrate 25cm3 samples of the olive oil solution with 0.025 mol dm3 Br2
, calculate a suitable mass of olive oil to transfer to the volumetric flask using your answer to 09.1
(7.5x10-4) moles of Br2) and the structure of Y.
assume that olive oil contains 85% of Y by mass.
(structure has 5 double bonded carbons)
[5 marks] - ANS-1) find the ratio of Br2 to Y:
5:1
2) find the moles of Y:
7.5x10-4/5= 1.5x10-4
3) find the moles in 250cm3:
1.5x10-4 x 10= 1.5x10-3
4) find the mass if the yield of Y was 100%:
1.5x10-3 x 880= 1.32g
5) find the mass of olive oil needed:
1.32 x (100/85) = 1.55g
A sample of rhenium is ionised by electron impact in a time of flight mass spectrometer.
A 185Re+ ion with a kinetic energy of 1.153x10-13J travels through a 1.450m flight tube.
The kinetic energy of the ion is given by the equation KE= 1/2mv^2
where
m= mass/ kg
v= speed/ m s-1
KE= kinetic energy/ J
calculate the time, in seconds, for the ion to reach the detector.
The Avogadro constant, L= 6.022x10^23 mol-1
[5 marks] - ANS-1) rearrange equation:
V= √2KE/m
2) find the mass of the ion:
(185/6.022x10^23)/1000 = 3.0721x10-25
3) substitute:
