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# Multiple choice A-level questions watch

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A, B, C, D

but not necessarily in that order
2. Answer for question 11 is C as 10% of the O2 reacts so that leaves 270cm^3 of oxygen and as the ratio of O2 to O3 is 3mol:2mol, we have 30cm^3 O2 reacting to produce 20cm^3 of O3 so there is 270+20=290cm^3 (c)

Answer for question 12 I think is B because (assuming that the ratio of alkene to dichloroalkane is 1mol:1mol) the formula for number of moles is n=mass/Mr which gives the equation for the number of moles of alkene = 1.40/14x where x is the number of carbons in the alkene and the number of moles of dichloroalkane = 3.77/(14x+2(35.5)) as chlorine has the Ar 35.5 so calculating these for each value of x possible (2,3,4,6) shows that x=3 gives the two closest values so B is the best solution (it is easier to think about as just trial and error for each of the given answers than to use this mathematical method but is more difficult for me to explain on here in words than the maths sorry if it is difficult to follow)

Answer for 9 is D as the number of moles of iron in the iron oxide is 1.12/56=0.02 and the number of moles of oxygen in the oxide is (1.6-1.12)/16=0.03 so the ratio of iron to oxygen is 2:3 so Fe2O3 is the answer
3. (Original post by MattSull)
Answer for question 11 is C as 10% of the O2 reacts so that leaves 270cm^3 of oxygen and as the ratio of O2 to O3 is 3mol:2mol, we have 30cm^3 O2 reacting to produce 20cm^3 of O3 so there is 270+20=290cm^3 (c)

Answer for question 12 I think is B because (assuming that the ratio of alkene to dichloroalkane is 1mol:1mol) the formula for number of moles is n=mass/Mr which gives the equation for the number of moles of alkene = 1.40/14x where x is the number of carbons in the alkene and the number of moles of dichloroalkane = 3.77/(14x+2(35.5)) as chlorine has the Ar 35.5 so calculating these for each value of x possible (2,3,4,6) shows that x=3 gives the two closest values so B is the best solution (it is easier to think about as just trial and error for each of the given answers than to use this mathematical method but is more difficult for me to explain on here in words than the maths sorry if it is difficult to follow)

Answer for 9 is D as the number of moles of iron in the iron oxide is 1.12/56=0.02 and the number of moles of oxygen in the oxide is (1.6-1.12)/16=0.03 so the ratio of iron to oxygen is 2:3 so Fe2O3 is the answer
Thanks! It all makes sense now

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