Mod 1B: Moles RE Test
1)
a)
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%
Iridium, atomic number 77, is a very dense metal. The relative masses of the isotopes
are shown below.
Explain the term isotopes. [2]
b)
Use the information in the table to calculate the relative atomic mass of the iridium in
this meteorite. Give your answer to one decimal place. [2]
Isotope
Abundance
%
191Ir
38
193Ir
62
c)
i)
Iridium reacts with fluorine to form a yellow solid Y with the percentage composition by
mass: Ir = 62.75%; F = 37.25%.
The empirical formula of Y can be calculated from this information.
Define the term empirical formula. [1]
ii)
Calculate the empirical formula of Y. [2]
2)
When magnesium oxide is added to warm dilute nitric acid, a reaction takes place:
MgO(s)
+
2HNO3(aq) 
Mg(NO3)2(aq) +
H2O(l)
a)
A student reacted 0.0500 moles of MgO with 0.400 mol dm-3 nitric acid.
i)
What would you see during this reaction? [1]
ii)
Calculate the mass of MgO that reacted. [2]
iii)
Calculate the volume of 0.400 mol dm-3 HNO3 required to react exactly with this
amount of MgO. [2]
3)
a)
The group 2 metal strontium, Sr, is very reactive.
The reaction of strontium with water is shown. A student reacted 0.438g of strontium
with 200cm3 of water.
Sr(s)
i)
+
2H2O(l)

Sr(OH)2(aq)
Calculate how many moles of Sr were reacted. [1]
Ar: Sr = 87.6
+
H2(g)
ii)
Calculate the volume in, dm3, of H2(g) produced. You can assume, that under the
experimental conditions, 1.00 Mol of H2(g) has a volume of 24.0 dm3. [1]
iii)
Calculate the concentration, in mol dm3, of the Sr(OH)2 produced. [1]
4)
A student had a stomach-ache and decided to take some Milk of Magnesia, which is
an aqueous suspension of magnesium hydroxide, Mg(OH)2.
Mg(OH)2(s)

2HCl(aq) 
MgCl2(aq)

H2O(l)
a) The student’s stomach contained 500 cm3 of stomach fluid with an acid
concentration of 0.108 mol dm–3. The student swallowed some Milk of Magnesia
containing 2.42 g Mg(OH)2. He wondered whether this dose was sufficient to
neutralise the stomach acid. Assume that all the acid in the stomach fluid was 0.108
mol dm–3 hydrochloric acid.
(i) How many moles of HCl were in the 500 cm3 of stomach fluid? [1]
(ii) Calculate the mass of Mg(OH)2 necessary to neutralise this stomach fluid. [3]
(iii)Determine whether the student swallowed too much, too little, or just the right
amount of Milk of Magnesia to neutralise the stomach acid. [1]
5) Antimony is found naturally in a number of minerals including stibnite. Stibnite typically
contains 5% of Sb2S3. Antimony can be obtained by reducing Sb2S3 with scrap iron.
Sb2S3
a) How many moles of Sb2S3 are in 500 kg of a typical sample of stibnite containing 5% by
mass of Sb2S3?
Mr Sb2S3 = 340 g mol–1; Ar Sb = 122 [2]
b) Calculate the mass of antimony that could be obtained by processing 500 kg of stibnite. [2]
6) Nickel makes up 25% of the total mass of a fifty pence coin. A fifty pence coin has a mass
of 8.0 g.
a) Calculate how many moles of nickel atoms are in a fifty pence coin. [2]
b) Calculate the number of atoms of nickel in a fifty pence coin.
[1]
L = 6.02  1023 mol–1