1
1
Compound X has the following composition by mass.
H, 3.66%; P, 37.80%; O, 58.54%
Calculate the empirical formula of compound X.
empirical formula = ........................... [2]
[Total: 2]
2
A student prepares magnesium sulfate crystals, MgSO4, by adding excess magnesium to dilute
sulfuric acid.
Magnesium sulfate crystals have the formula, MgSO4•xH2O, where x is a whole number of molecules
of water.
The student heats the crystals to remove the molecules of water.
MgSO4•xH2O(s) → MgSO4(s) + xH2O(g)
The student heats a sample of MgSO4•xH2O and finds it has lost 0.140 moles of H2O and has
2.40 g of MgSO4 remaining.
Determine the value of x .
Use the following steps.
(a) Calculate the Mr of MgSO4.
Mr = .................................. [1]
(b) Determine the number of moles of MgSO4 formed.
moles of MgSO4 formed = ........................... [1]
2
(c) Determine the value of x in MgSO4•xH2O.
x = .................................... [1]
[Total: 3]
3
When potassium is added to water, it reacts vigorously and a coloured flame is seen.
The equation for the reaction is shown.
2K(s) + 2H2O(l) → 2KOH(aq) + H2(g)
3
(a) Calculate the volume, in cm , of hydrogen gas formed when 2.34 g of potassium is added to
excess water at room temperature and pressure.
Use the following steps.
(i)
Calculate the number of moles of potassium added.
= .......................................................mol [1]
(ii) Determine the number of moles of hydrogen gas formed.
= .......................................................mol [1]
3
(iii) Calculate the volume of hydrogen gas formed.
3
volume = ..........................................cm
[1]
[Total: 3]
4
Calcium nitrate crystals are hydrated and have the formula Ca(NO3)2•xH2O where x is a whole
number of molecules of water.
The student heats the crystals to remove the molecules of water.
Ca(NO3)2•xH2O(s) → Ca(NO3)2(s) + xH2O(g)
The student heats a sample of Ca(NO3)2•xH2O and forms 2.46 g of Ca(NO3)2 and 0.0600 moles
of H2O.
Determine the value of x. Use the following steps.
(a) Calculate the Mr of Ca(NO3)2.
Mr = ................................................ [1]
(b) Determine the number of moles of Ca(NO3)2 formed.
moles of Ca(NO3)2 formed = ........................ [1]
4
(c) Determine the value of x in Ca(NO3)2•xH2O.
x = .................................................. [1]
[Total: 3]
5
Compound Y has the empirical formula H3PO4 and a relative molecular mass of 98.
Deduce the molecular formula of compound Y.
molecular formula = .......................... [1]
[Total: 1]
6
Fluorine reacts with sulfur to form a compound which has 25.2% sulfur by mass and a relative
molecular mass of 254.
Determine the molecular formula of this compound.
molecular formula = ......................................... [3]
[Total: 3]
5
7
3
Determine the volume of CO2 gas given off when excess MgCO3 is added to 25.0 cm of
3
0.400 mol / dm HCl at room temperature and pressure.
MgCO3 + 2HCl → MgCl2 + H2O + CO2
Use the following steps.
•
3
3
Calculate the number of moles of HCl in 25.0 cm of 0.400 mol / dm of acid.
.................................... m o l
•
Determine the number of moles of CO2 gas given off.
.................................... m o l
•
3
Calculate the volume of CO2 gas given off in cm .
.................................... cm
3
[3]
[Total: 3]
8
When solid copper(II) nitrate is heated copper(II) oxide, nitrogen dioxide and oxygen are formed.
2Cu(NO3)2 → 2CuO + 4NO2 + O2
Calculate the volume of nitrogen dioxide formed at room temperature and pressure when 4.7 g of
Cu(NO3)2 is heated.
Use the following steps:
(a) Calculate the mass of one mole of Cu(NO3)2.
............................... g [1]
6
(b) Calculate the number of moles of Cu(NO3)2 used.
........................ moles [1]
(c) Determine the number of moles of nitrogen dioxide formed.
........................ moles [1]
(d) Calculate the volume of nitrogen dioxide formed at room temperature and pressure.
3
........................... dm
[1]
[Total: 4]
9
The Avogadro constant is the number of particles in 1 mole.
23
The numerical value of the Avogadro constant is 6.02 x 10 .
(a) Calculate the number of molecules in 22.0 g of carbon dioxide, CO2.
.......................................molecules [2]
7
3
(b) Calculate the number of molecules in 6.00 dm of carbon dioxide gas at room temperature
and pressure.
.......................................molecules [1]
[Total: 3]
10 Lead is a metallic element in Group IV. One of the ores of lead is galena, which is an impure form
of lead(II) sulfide, PbS.
Lead also occurs in the ore cerussite, which contains lead(II) carbonate, PbCO3.
(a) Calculate the relative formula mass, Mr, of PbCO3.
Mr of PbCO3 = .............................................. [1]
(b) The Mr of PbS is 239.
Calculate the percentage of lead by mass in PbS.
percentage of lead by mass in PbS = .......... [1]
[Total: 2]
8
11
Many organic compounds contain carbon, hydrogen and oxygen only.
An organic compound R has the following composition by mass.
C, 69.77%;
H, 11.63%;
O, 18.60%
Calculate the empirical formula of compound R.
empirical formula = ........................... [2]
[Total: 2]