Amount of substance

Question 1

Avogrado’s constant

Answer 1

Number of particles = number of moles x avogrado’s constant

Question 2

Mole equations

Answer 2

Mass of substance = number of moles x Mr

Question 3

Calculating number of moles

Answer 3

Concentration x volume (cm3) / 1000 = number of moles

Question 4

Calculating number of moles second equation

Answer 4

Number of moles = concentration x volume (dm3)

Question 5

Gas equation

Answer 5

pV = nRT

Question 6

Breakdown of gas equation

Answer 6

p = pressure (Pa)
V = volume (m3)
n = number of moles
R = gas constant (8.31)
T = temperature in K (+273)

Question 7

Rearranging gas equation

Answer 7

pV = nRT
n = pV / RT
p = nRT / V
V = nRT / P
T = pV / nR

Question 8

The vanadium in 50.0 cm3 of a 0.800 mol dm−3 solution of NH4VO3 reacts with 506 cm3 of sulfur(IV) oxide gas measured at 20.0 °C and 98.0 kPa.
Use this information to calculate the oxidation state of the vanadium in the solution after the reduction reaction with sulfur(IV) oxide.
Explain your working.
The gas constant R = 8.31 J K−1 mol−1.

Answer 8

PV/RT
P = 98 000 V = (506=10’-6) R = 8.31 T = 293
98000 x (506 x 10’-6) / 8.31 x 293 = 2.04 x 10-2
When SO2 acts as a reducing agent, it is oxidised to sulfate ions so this is a two electron change
Moles of electrons released when SO2 is oxidised = 2.04 x 10-2 x 2 = 4.08 x 10-2
Vanadium is in oxidation state 4

Question 9

Analysis of a pure sample of citric acid showed that it contained 37.50% of carbon and 4.17% of hydrogen by mass, the remainder being oxygen. Use these data to
show that the empirical formula of the acid is C6H8O7

Answer 9

(37.5+4.17) - 100 = 58.33%
Carbon = 37.5/12 = 3.125
Hydrogen = 4.2/1 = 4.17
Oxygen = 58.88/16 = 3.645

Question 10

When the antacid tablet is added to water, sodium hydrogencarbonate and citric acid react together to form a gas. Identify this gas

Answer 10

Carbon dioxide

Question 11

Which of the following contains the most chloride ions?
A) 10 cm3 of 3.30 × 10−2 mol dm−3 aluminium chloride solution
B) 20 cm3 of 5.00 × 10−2 mol dm−3 calcium chloride solution
C) 30 cm3 of 3.30 × 10−2 mol dm−3 hydrochloric acid
D) 40 cm3 of 2.50 × 10−2 mol dm−3 sodium chloride solution

Answer 11

A

Question 12

A second sample of nitroglycerine was placed in a strong sealed container and detonated. The volume of this container was 1.00 × 10–3 m3. The resulting decomposition produced a total of 0.873 mol of gaseous products at a temperature of 1100K.
State the ideal gas equation and use it to calculate the pressure in the container after detonation.
Gas constant = 8.31

Answer 12

P = nRT/V
(0.873 x 8.31 x 1100) / (1 x 10’-3) = 7980093 Pa or 7980 kPa

Question 13

A sample of 2.18 g of oxygen gas has a volume of 1870 cm3 at a pressure of 101 kPa. What is the temperature of the gas?
The gas constant is R = 8.31 J K–1 mol–1.

Answer 13

334K

Question 14

Write the ionic equation for
Fe(s) + CuSO4(aq) -> FeSO4(aq) + Cu

Answer 14

Fe + Cu2+ -> Fe2+ + Cu