Quantitative Chemistry (Part 2) - Unit 2 Topic 6

Question 1

How do you calculate the percentage of an element in a compound?

Answer 1

Mass of element in 1 mole of compound (RAM)
———————————————- x 100
Mass of 1 mole of compound (RFM)

Question 2

Calculate the percentage by mass of Carbon in Pentene
C5H10
C = 12
H = 1

Answer 2

60/70 x 100 = 85.7%

Question 3

What does it mean if something is an aqueous solution?

Answer 3

Dissolved in water

Question 4

What is the concentration of a solution?

Answer 4

A measure of how much of a substance is dissolved in a known volume of water.

Question 5

What are the units of concentration?

Answer 5

Moles per litre (mol/l) or moles per dm3 (mol/dm3)

Question 6

How many dm3 is 1 litre.

Answer 6

1 dm3

Question 7

What is the formula triangle for c, n, v.

Answer 7

Conc|volume

Question 8

Calculate the concentration of a solution which contains 0.5 mol of solute dissolved in 1dm3 of water.

Answer 8

C=n/v
C = 0.5/1
C = 0.5mol/dm3

Question 9

What is the formula triangle for m, n, RFM?

Answer 9

No moles / RFM

Question 10

Calculate the mass of sodium hydroxide which when dissolved in 1dm3 of water will produce a solution with a concentration of 0.1mol/dm3.

Answer 10

N = c x v = 0.1 x 1 = 0.1 mol
M = n x RFM = 0.1 x 40 = 4g

Question 11

What happens when a solution is diluted?

Answer 11

The concentration changes

Question 12

How do you calculate the new concentration of the acid when it has been diluted?

Answer 12

Original concentration
———————- = New concentration
Dilution factor

Question 13

A 1mol/dm3 solution of hydrochloric acid was diluted by a factor of 10. What is the new concentration of the acid?

Answer 13

O/d = n
1/10 = 0.1mol/dm3

Question 14

Calculate the dilution factor when a 4mol/dm3 solution of NaOH is diluted to a new concentration of 0.1mol/dm3.

Answer 14

N = 0/df
0.1 = 4/df
DF = 40

Question 15

Calculate the dilution factor when a 4mol/dm3 solution of sodium hydroxide is diluted to a new concentration of 0.1mol/dm3. Calculate the concentration of the HCl.

Answer 15

NaOH HCl
Conc| 0.125 0.145
N| 0.003125 0.003125
V| 0.025 0.0216

Concentration = 0.145 mol/dm3

Question 16

What are titrations used for?

Answer 16

Finding out the volume of one liquid which will react with a known volume of another.

Question 17

How many decimal places should a titration result be recorded to?

Answer 17

1

Question 18

What are concordant results?

Answer 18

Ones that differ by less than 0.1cm3.

Question 19

What units can you use for titration solutions?

Answer 19

Mol/dm3

G/dm3

Question 20

What are the colours in acid + alkali of phenolphthalein?

Answer 20

Acid = Colourless 
Alkali = pink

Question 21

What are the colours in acid and alkali of methyl orange?

Answer 21

Acid = orange
Alkali = yellow

Question 22

Describe, in detail, how you would transfer 25cm3 alkali into a conical flask using a pipette.

Answer 22

Rinse pipette with deionised water then with alkali using pipette filler. Fill pipette above line using pipette filler and release alkali into conical flask.