ENGINEERING CHEMISTRY 123
2019’s A3 Memorandum
2021
(FYI if you only wrote down these answers you would not receive full marks. Many marks are
awarded for calculation, methodology and logic)
QUESTION 1
1.1) e
1.2) a
1.3) b
1.4) c
1.5) e
1.6) c
1.7) b
1.8) c
1.9) b
1.10) d
QUESTION 2
2.1.
2.2. pOH = 2.00
2.3.
2.4. i) False, ii) False
2.5. Fe2O3
Oxidation state of Fe = +3
2.6. [OH ] = 1.7 x 10-4 mol/L
2.7. Gas is Oxygen
QUESTION 3
i)
ii)
iii)
Use redox balance method to get balanced reaction
nNO = 0.175 mol NO
nN2 = 0.242 mol N2
PN2 = 365 kPa
PNO = 235 kPa
QUESTION 4
i)
ii)
Solubility = 1.35 x 10-3 mol/L PbI2
Qsp>Ksp so precipitation does occur
Bonus: to prevent iodine deficiency
QUESTION 5
i)
ii)
% ionization = 0.64%
Temperature should be decreased to favour forward reaction, since this reaction is
exothermic (with ehat as a product) and le chattelier’s principle favours the forward
reaction when heat is removed.