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Practice
exercises
Francine
Taylor-Campbell, Contributor
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| All
ready to go on the canopy tour, high above the trees. One of the off-site activities
offered by New Generation summer camps. - Contributed photos |
Practice exercises1.
Two moles of sulphuric acid react with one mole of sodium carbonate to form a
salt, water and carbon dioxide. Write
a balanced equation for this reaction.
(2 marks) Is
the salt formed, an acid salt or a normal salt? Give a reason for your answer.
(2 marks) Calculate
the mass of the salt formed when 10.6g of sodium carbonate are used in the reaction.
(Relative atomic mass: Na = 23, C = 12, O = 16, S = 32, H = 1) (2 marks) Answers:
1.
(i) 2H2SO4 + Na2CO3
== NaHSO4 + H2O + CO2 (ii)
An acid salt is formed since it contains hydrogen ions (using the mole ratio given
only an acid salt could be formed). (iii
) Molar mass of Na2CO3 = (23*2) +
12 + (16*3) = 106g 10.6g of Na 2 CO 3 = 0.1 mol (10.6/106) Based
on the equation 1 mol Na2 CO3 produce
1 mol of salt. Therefore, 0.1 mol Na 2 CO 3 produces 0.1 mol NaHSO 4 Molar
mass of NaHSO 4 = 23 + 1 + 32 + 16*4 = 120g Mass
of 0.1 mol of NaHSO4 = 0.1 x 120 = 12g 2.
Sodium reacts with ethanol at room temperature and pressure according to the following
equation: 2 Na(s) + 2 C2H5OH(i)
== 2 C2H5ONa
(s) + H2 (g) What
volume of hydrogen at r.t.p. can be produced when 11.5g sodium react with excess
ethanol? (2 marks)
 |
| Mountain
biking is another off-site activity offered by New Generation Camp in St. Ann,
through Chukka Adventure Tours. | Answers:
2.
First of all, we must determine how many moles of sodium are present. Molar
mass of Na = 23g, thus 11.5g = 11.5/23 = 0.5 mol Na Based
on the equation, 2 mol Na give off 1 mol H2
gas (2:1 ratio) Thus
0.5 mol Na will produce 0.25 mol H2 1
mol H2 at r.t.p. == 24 dm³ 0.25
mol H2 = 0.25 x 24 = 6 dm³.
3. Sodium
carbonate, carbon dioxide and water are produced when sodium hydrogen carbonate
is heated. Write an equation for the reaction. What is the maximum volume of carbon
dioxide that could be produced at room temperature and pressure on heating 21g
of sodium hydrogen carbonate? (4 marks) Answers:
2NaHCO3
(s) ==== Na2CO3 (s) + CO2
(g) + H2O-(l) Molar
mass of NaHCO3 = 23 + 1 + 12 + 16*3 = 84g 21g
of NaHCO3 = 0.25 mol = 21/84 Based
on the equation, 2 mol of NaHCO3 produce 1 mol CO2
Thus
0.25 mol NaHCO3 will produce 0.125 mol CO2
At r.t.p.
1 mol CO2 has a volume of 24 dm3 0.125
mol CO2 = 0.125 x 24 = 3 dm 4.
A sample of calcium carbonate is heated to constant mass. Write an equation to
represent this reaction. Calculate the mass of solid residue that would be obtained
if 10g of calcium carbonate were heated. (5 marks) Answers:
CaCO3
(s) CaO (s) + CO2 (g) Mr
of CaCO3 = 40+12+(16*3) = 100 g; #mol
in 10 g = 10/100 = 0.1 mol CaCO 3 . Based
on equation, CaCO3 reacts to produce CaO
(solid) in a 1:1 ratio Hence
#mol of CaO formed = 0.1 mol Mr
of CaO = 40+16 = 56 Mass
of 0.1 mol = 56*0.1 = 5.6 g CaO Francine
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