Q20.
(a) Weigh the spirit burner (alcohol) before and after combustion M1
Do not allow “a known mass of alcohol” owtte
1
Water in a calorimeter / beaker M2
1
Measure volume of water (or mass) M3
1
Burn the alcohol to heat the water M4
1
Measure temperature rise in water M5
1
(b) Incomplete combustion
Evaporation of alcohol
Heat capacity of / heat absorption by the apparatus
Inadequate stirring
Any two correct
1
1
(c) Acidified potassium dichromate / manganate(VII) (Heat)
Allow sodium in place of potassium with appropriate colour change)
If reagent incomplete lose M1 but mark on.
If reagent incorrect, CE = 0/3
1
butan-1-ol orange to green / purple to colourless
1
2-methylpropan-2-ol NVC / orange / purple
1
(d) C4H9OH + 2O2 → 4C + 5H2O
OR
C4H9OH + 4O2 → 4CO + 5H2O
Allow any correct balanced equations which include combinations of C, CO and/or CO2 in the products but must be incomplete combustion.
1
Engine would not run as efficiently / would need to use more fuel / would release less energy
Allow build-up of carbon in engine costly to remove
1
CO / Particulates of carbon toxic
Allow global dimming if carbon given as product
1
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