1
1
135 moles of urea, (NH2)2CO, is stored in the tank of a car.
Calculate the mass, in kg, of the stored (NH2)2CO.
mass of (NH2)2CO = ................................ kg [2]
[Total: 2]
2
Some chlorides are hydrated.
When hydrated barium chloride crystals, BaCl2•xH2O, are heated they give off water.
BaCl2•xH2O(s) → BaCl2(s) + xH2O(g)
A student carries out an experiment to determine the value of x in BaCl2•xH2O.
In an experiment, 4.88 g of BaCl2•xH2O is heated until all the water is given off. The mass of BaCl2
remaining is 4.16 g.
[Mr: BaCl2, 208; H2O, 18]
Determine the value of x using the following steps.
•
Calculate the number of moles of BaCl2 remaining.
................................... mol
•
Calculate the mass of H2O given off.
....................................... g
•
Calculate the number of moles of H2O given off.
................................... mol
•
Determine the value of x.
x = .................................... [4]
[Total: 4]
2
3
When hydrated magnesium sulfate crystals, MgSO4•xH2O, are heated they give off water.
MgSO4•xH2O(s) → MgSO4(s) + xH2O(g)
A student carries out an experiment to determine the value of x in MgSO4•xH2O.
Step 1 Hydrated magnesium sulfate crystals were weighed.
Step 2 Hydrated magnesium sulfate crystals were heated.
Step 3 The remaining solid was weighed.
(a) Describe how the student can ensure that all the water is given off.
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
[2]
(b) In an experiment, all the water was removed from 1.23 g of MgSO4•xH2O. The mass of MgSO4
remaining was 0.60 g.
Mr: MgSO4 = 120; Mr: H2O = 18
Determine the value of x using the following steps.
•
Calculate the number of moles of MgSO4 remaining.
moles of MgSO4 = ........................
•
Caluculate the mass of H2O given off.
mass of H2O = ......................... g
•
Calculate the moles of H2O given off.
moles of H2O = .............................
•
Determine the value of x.
x = .................................. [4]
[Total: 6]
3
4
PCl5 reacts with lithium fluoride, LiF, to form LiPF6.
PCl5 + 6LiF → LiPF6 + 5LiCl
Calculate the mass of LiF needed to form 3.04 g of LiPF6 using the following steps.
• Calculate the number of moles of LiPF6 formed.
[Mr: LiPF6, 152]
number of moles = .........................................
• Deduce the number of moles of LiF needed.
number of moles = .........................................
• Calculate the mass of LiF needed.
mass = ................................ g [3]
[Total: 3]