Unit C2, C2.3.3 Quantitative chemistry
1.
A student heated some hydrated copper sulfate crystals.
The equation for this reaction is shown below.
CuSO4.5H2O(s)
hydrated copper sulfate crystals
CuSO4(s)
+
5H2O(1)
anhydrous copper sulfate
water
The diagram shows the apparatus used.
Hydrated copper sulfate crystals
Vapour
Heat
Ice cube
Liquid A
(a)
Name liquid A ......................................................................
(1)
(b)
What helped the vapour to condense into liquid A?
.....................................................................................................................................
(1)
(c)
Put a tick (
) next to the correct meaning of the symbol
(
Meaning
)
equal amounts of reactants and products
exothermic reaction
reversible reaction
(1)
(d)
The student weighed the copper sulfate before and after it was heated.
The experiment was repeated and the two sets of results are shown in the table.
Page 1 of 4 Mass of copper sulfate
before heating in grams
Mass of copper sulfate
after heating in grams
Mass lost in grams
2.50
1.65
0.85
2.50
1.61
0.89
Unit C2, C2.3.3 (i)
Draw a ring around the average mass lost for these two sets of results.
0.85 g
0.87 g
0.89 g
(1)
(ii)
The student used the same mass of copper sulfate each time but the mass lost was
different.
Put a tick (
different.
) next to the two reasons which could explain why the mass lost is
Reason
(
)
The student used different test tubes for the two experiments.
The student made errors in weighing during the experiments.
The student used more ice in one of the experiments.
The student did not heat the copper sulfate for long enough in one of
the experiments.
(2)
(Total 6 marks)
2.
Toothpastes often contain fluoride ions to help protect teeth from attack by bacteria.
Some toothpastes contain tin(II) fluoride.
This compound has the formula SnF2 .
(a)
Calculate the relative formula mass (Mr) of SnF2.
Relative atomic masses: F = 19; Sn = 119
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
Relative formula mass (Mr) = ..........................................
(2)
Page 2 of 4 Unit C2, C2.3.3 (b)
Calculate the percentage by mass of fluorine in SnF2.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
Percentage by mass of fluorine = .......................................... %
(2)
(c)
A tube of toothpaste contains 1.2 g of SnF2 .
Calculate the mass of fluorine in this tube of toothpaste.
....................................................................................................................................
....................................................................................................................................
....................................................................................................................................
Mass of fluorine = .......................................... g
(1)
(Total 5 marks)
3.
This cake recipe is taken from a cookery book.
Soda Cake
• Mix the flour and butter and add the sugar, currants and flavouring.
• Then add the beaten egg.
• Add a little milk with a teaspoonful of baking soda (sodium hydrogencarbonate)
and mix it in well.
• Bake in a moderate oven for about 30 minutes.
When sodium hydrogencarbonate is heated in an oven, it forms carbon dioxide gas.
2 NaHCO3
Heat
⎯⎯
⎯→ Na2CO3 + H2O + CO2
A teaspoonful of baking soda contains a mass of 11 g of sodium hydrogencarbonate.
Calculate the mass of carbon dioxide that could be made from 11 g of sodium hydrogencarbonate.
Show clearly how you work out your final answer.
Relative atomic masses: H = 1; C = 12; O = 16; Na = 23.
...............................................................................................................................................
...............................................................................................................................................
...............................................................................................................................................
Mass of carbon dioxide = ............................................... g
(Total 3 marks)
Page 3 of 4 Unit C2, C2.3.3 4.
Cosmetic powders were widely used in ancient Egypt.
Cosmetic powders that may have been used in face paints have
been analysed. These powders contained compounds that are rare
in nature. The compounds must have been made by the ancient
Egyptians using chemical reactions.
One of these compounds is called phosgenite.
Analysis of this compound shows that it contains:
76.0% lead (Pb)
13.0% chlorine (Cl)
2.2% carbon (C)
8.8% oxygen (O)
Calculate the empirical formula of this compound.
To gain full marks you must show all your working.
Relative atomic masses: C = 12 ; O = 16 ; Cl = 35.5 ; Pb = 207
...................................................................................................................................
...................................................................................................................................
...................................................................................................................................
...................................................................................................................................
...................................................................................................................................
...................................................................................................................................
...................................................................................................................................
...................................................................................................................................
(4)
(Total 4 marks)
Page 4 of 4