Moles 3 - solutions

Question 1

phenolphthalein and methyl orange indicators in acids and alkali

Answer 1

Phenolphthalein:
In acid: colourless
In alkali: pink

Methyl orange:
In acid: red/orange
In alkali: yellow

Question 2

Calculating solution concentrations in mol/dm^3

Answer 2

Concentration = moles / volume (dm^3)

Question 3

Calculating solution concentrations in g/dm^3

Answer 3

Concentration = mass / volume (dm^3)

Question 4

Calculating volume of gases

Answer 4

Volume of gas (dm^3) = moles x 24

Question 5

Converting between mg, g, kg and tonnes

Answer 5

g –> mg -x10^3
kg –> mg x10^6
tonnes –> mg x10^9

Question 6

Calculating uncertainty

Answer 6

% uncertainty = +/- (uncertainty/measurement made on apparatus)*100

balance - 0.001g
volumetric flask - 0.1cm^3
25cm^3 pipette - 0.1cm^3
burette - 0.05cm^3

Question 7

Methods to decrease apparatus uncertainties

Answer 7

1. Using apparatus with a greater resolution
2. Increase the size of the measurement made

Question 8

Calculating percentage difference

Answer 8

% difference = (difference between actual value and calculated value/calculated value)*100