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Questions on Qualitative Analysis – Assignment 2 – Answers
Question One:
a)
Barium ion, Ba2+
b)
B Barium sulfate, BaSO4
C Sodium bromide, NaBr
D Barium carbonate, BaCO3
E Silver bromide, AgBr
F Bromine, Br2
A Barium bromide, BaBr2
c)
BaBr2(aq) + Na2CO3(aq)  BaCO3(s) + 2NaBr(aq)
d)
Carbon dioxide, CO2
e)
Cl2(aq) + 2Br–(aq)  2Cl–(aq) + Br2(aq)
This is a redox reaction. The chlorine is reduced to chloride while the bromide is oxidised to bromine.
Question Two:
a)
FeCl3(aq) + 3NaOH(aq)  Fe(OH)3(s) + 3NaCl(aq)
b)
● Between 1.0 and 5.0 cm 3 of sodium hydroxide, the iron(III) chloride is in excess. This can be seen
because the level of the precipitate increases.
● At 6.0 cm3 of sodium hydroxide, the ratio of sodium hydroxide to iron(III) chloride is correct for both
chemicals to react completely.
● Between 7.0 and 10.0 cm3 of sodium hydroxide, the sodium hydroxide is in excess. This can be
seen because the level of the precipitate remains almost constant.
● Therefore, 5.0 cm 3 of FeCl3 reacts with 6.0 cm 3 of NaOH.
● moles of NaOH = c  v  10–3 = 0.1  6.0  10–3 = 0.0006
● From the balanced chemical equation:
moles of FeCl3 = moles of NaOH  3 = 0.0006  3 = 0.0002
● Therefore, there are 0.0002 mol of FeCl3 in 5.0 cm3 of solution.
moles of FeCl3 in 1000 cm3 = (0.0002  5)  1000 = 0.04 = 0.04 mol dm–3
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Question Three:
a)
P Lead(II) iodide, PbI2
Q Calcium hydroxide, Ca(OH)2
R Zinc chloride, ZnCl2
S Hydrogen, H2
T Silver chloride, AgCl
X Calcium Iodide (CaI2) and zinc (Zn)
b)
Pb(NO3)2(aq) + CaI2(aq)  PbI2(s) + Ca(NO3)2(aq)
c)
Ca2+(aq) + 2OH–(aq)  Ca(OH)2(s)
d)
ZnCl2(aq) + 2AgNO3(aq)  Zn(NO3)2(aq) + 2AgCl(s)
Question Four:
a)
A Copper(II) carbonate, CuCO3
B Carbon dioxide, CO2
C Calcium carbonate, CaCO3
D Copper(II) oxide, CuO
E Sulphuric acid, H2SO4
F Copper(II) sulfate, CuSO4
G Barium sulfate, BaSO4
H Copper(II) hydroxide, Cu(OH)2
I Zinc, Zn
J Copper, Cu
K Zinc sulfate, ZnSO4
L Zinc oxide, ZnO
M Sulphur trioxide or sulphur(VI) oxide, SO3
b)
CuCO3(s)  CuO(s) + CO2(g)
c)
CuSO4(aq) + Ba(NO3)2(aq)  Cu(NO3)2(aq) + BaSO4(s)
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