Chemistry Reference
In-Depth Information
The equation for the reaction is:
→
Questions
Use the following
A
r
values to answer the questions below:
O
=
16; Mg
=
24; S
=
32; K
=
39; Cu
=
63.5.
1
Calculate the mass of sulfur dioxide produced by burning
16 g of sulfur in an excess of oxygen in the Contact
process (see p. 199).
2
Calculate the mass of sulfur which, when burned in
excess oxygen, produces 640 g of sulfur dioxide in the
Contact process.
3
Calculate the mass of copper required to produce 159 g
of copper(ii)
ii
) oxide when heated in excess oxygen.
4
In the rocket mentioned previously in which hydrogen is
used as a fuel, calculate the volume of hydrogen used to
produce 24 dm
3
of water (H
2
O(
g
)).
5
Calculate the volume of 2 mol dm
−3
solution of sulfuric
acid required to react with 24 g of magnesium.
6
What is the concentration of potassium hydroxide
solution used in the following neutralisation reaction?
20 cm
3
of 0.2 mol dm
−3
solution of hydrochloric acid just
neutralised 15 cm
3
of potassium hydroxide solution.
+
+
2NaHCO
3
(
s
)
Na
2
CO
3
(
s
)
H
2
O(
g
)
CO
2
(
g
)
2 moles 1 mole
Step 1: Calculate the RFM of sodium
hydrogencarbonate (
A
r
: Na = 23; C = 12;
O = 16; H = 1)
RFM of NaHCO
3
= 84
Step 2: 2 moles of NaHCO
3
produces 1 mole
of CO
2
.
168 g of NaHCO
3
would give 44 g of CO
2
,
which would have a volume of
24 dm
3
at rtp.
84 g of NaHCO
3
should give 12 dm
3
of CO
2
at rtp.
Hence the mass of NaHCO
3
in the
sample was 84 ×
11.5
12
= 80.5 g
Step 3: Calculate the percentage purity.
There is 80.5 g of sodium
hydrogencarbonate in the 84 g sample.
Percentage purity =
80.5
84
× 100% = 95.8%
Checklist
After studying Chapter 4 you should know and understand the following terms.
•
Avogadro's Law
Equal volumes of all gases measured under the same conditions
of temperature and pressure contain equal numbers of molecules.
•
Calculating moles
of compounds
mass of compound
(in grams)
=
number of
moles
×
mass of 1 mole
of compound
number of moles
=
mass of compound
mass of 1 mole of compound
•
Calculating moles of elements
mass of element
(in grams)
×
mass of 1 mole
of the element
number of moles
=
mass of the element
mass of 1 mole of that element
•
Calculating moles of gases
1 mole of any gas occupies 24 dm
3
(litres) at room temperature and pressure (rtp).
number of moles of gas
=
volume of the gas (in dm
3
at rtp)
24 dm
3
=
number of
moles
•
Calculating moles of solutions
concentration of a solution (in mol dm
−3
)
=
number of moles of solute
volume (in dm
3
)
=
×
number of
moles
concentration
(in mol dm
−3
)
volume of solution
(in dm
3
)
