Chemistry Form 12
1. (10 points) The principle of a fireworks-type explosion can be demonstrated by igniting a sucrose
jellybaby with sodium chlorate, NaClO3.
a. The explosion reaction.
i) Balance the equation for the explosion reaction:
....NaClO3(s) + C12H22O11(s) → .....NaCl(s) + ......C(s) + ......CO2(g) + ......H2O(g) 1 point
ii) What is the oxidation state of Cl in NaClO3? 1 point
iii) Determine oxidizer and reducer in this reaction. 2 points
b. During this reaction 2191 kJ of heat was released then 1 mol of C12H22O11 is exploded. Calculate the
quantity of heat released when one jelly-baby containing 4.56 g of sucrose (C12H22O11) was exploded. The
heat released by the explosion can be used to vaporise strontium chloride to give the fireworks red colour.
The heat required to convert SrCl2 from the solid to the gas state is 343 kJ/mol. Calculate the mass of solid
SrCl2 that can be vaporised by exploding one jelly baby containing 4.56 g of sucrose. 3 points
c. Barium nitrate is one of the components of ‘sparklers’. It gives the bengal fire green colour. During the
combustion reaction barium nitrate reacts with aluminum. Barium and aluminum oxides, and nitrogen are
created. Write chemical equation for this reaction, balance it and determine physical forms of all
compounds. 3 points
2. (12 points) Student added 20ml of 0.1 mol/l potassium hydroxide solution to 20ml of 0.1 mol/l sulphuric
acid.
pipett
e
20ml of 0.1mol/l potassium
hydroxide solution
beaker
r
20ml of 0.1 mol/l
sulphuric acid
a. Identify which of the following statement(s) is/are R-right and which is/are wrong W-wrong. 6 points
A
B
C
D
E
F
The number of SO42-(aq) ions in the beaker decreased.
The final solution has equal numbers of H+(aq) and OH-(aq) ions.
The number of H+(aq) ions in the beaker decreased.
A precipitate formed during the reaction.
Water molecules formed during the reaction.
The pH of the solution decreased.
b. To the obtained solution student added additional 10 g of 5 % sodium hydroxide solution. What could be
pH of the final solution (>7; <7 or =7)? Show all steps. 6 points
3. (8 points) Archeologists found some corroded silver coins and a badly rusted sword.
a. The silver coins were restored by wrapping them in zinc foil and put them in a beaker of salt solution.
What type of reaction took place? 1 point
b. The iron blade of the sword was attached to its handle by a copper band. Explain why, although the
copper was uncorreded, the iron had rusted badly. 1 point
c. Iron has several isotopes. One of them has the electronic configuration [Ar]3d64S2, an atomic number of
26 and a mass number of 56.
i) Which of these pieces of information would be the most use in helping a chemist decide on the
likely chemical reactions of iron? 1 point
ii) Write the electronic configuration of Ar. 1 point
d. Before now “silver“ coins were made from an alloy of silver, copper and nickel. To determine the silver
composition, a coin weighing 10,00 g was dissolved in nitric acid and the resulting solution diluted to 1000
ml in a standard flask. 0.20 mol/l hydrochloric acid was added to 100 ml of this solution until precipitation
of silver(I) chloride was complete. The precipitate was recovered by filtration, washed, dried and found to
have a mass of 0.60 g.
i)Calculate the percentage by mass of silver in the coin. 3 points
ii) How would you confirm that precipitation was complete. 1 point
4. (13 points) The hydrocarbons present in a mixture can be separated using chromatography. The mixture
is vapourised and is then passed through a special column. Different hydrocarbons move through the
column at different speeds. The following graph was obtained.
C
E
B
D
A
F
a. How many different molecular formulas are needed to describe all hydrocarbons shown in the graph?
Write all of them. 4 points
b. Give names for D and E compounds using IUPAC nomenclature rules. 2 points
c. Make two general statements linking the structure of hydrocarbon with the length of time taken to pass
through the column. 2 points
d. Predict position of the peak in this graph for propane if it were been in original hydrocarbons mixture. 1
point
e. One of these hydrocarbons was completely burnt and 44.4 % CO2 (by volume) were generated in the gas
mixture. Which one it was? 4 points
5. (6 points) Provide one good example for:
a. Reaction: alkane
alkene 1 point
b. Reaction: alkene
alcohol 1 point
c. Aromatic compound: 1 point
d. Hydrocarbon capable to decolourize bromine water: 1 point
e. Water-soluble organic compound: 1 point
f. Alkyne synthesis reaction: 1 point