Chemistry Form 10
1. (6 points) The flow diagram shows tests that can be used to identify carbonate, chloride and sulfate ions
present in a sample.
Write balanced identification equations for all reactions in these steps in ionic and overall forms.
2. (11 points) Bone consists of a complex mixture of calcium salts, such as calcium carbonate, and other
material. If bone is strongly heated, the calcium carbonates turn into calcium oxide, CaO. This can be
separated from the other material by dissolving it in dilute hydrochloric acid, to form calcium chloride,
CaCl2, solution.
a. Write complete and balanced chemical equations showing state symbols for these reactions. 2 points
b. An experiment showed that 14.4 g of calcium oxide were made from a sample of bone of mass 50.0 g.
Calculate the % of calcium by mass in the bone. Calculate the not used amount of hydrochloric acid in the
reaction in g, if obtained calcium oxide was completely dissolved in 100 ml 20 % of dilute hydrochloric acid.
Hydrochloric acid solution density is 1.1 g/ml. 6 points
c. Strontium compounds are incorporated into bones because their chemistry is similar to that of calcium
compounds. For example, both strontium and calcium form ions with the same charge. Explain, in terms of
the Periodic Table, the electronic structures of the atoms why calcium and strontium (and their
compounds) have similar chemical properties. 3 points
3. (8 points) Below a part of Periodic Table with few elements is shown in figure. Answer the following
questions by using just these elements.
a. Write a molecular formula for a compound which has a covalent polar bond.
b. Write a molecular formula for a compound which has a covalent nonpolar bond and is in gas state under
normal conditions.
c. Write a molecular formula for a compound which has an ionic bond.
d. Which two of these elements have similar chemical properties?
e. Write a molecular formula for a compound which has high melting point.
f. Which element is conductive to electricity and heat?
g. Which element is chemically inactive?
h. Write a molecular formula for a compound which is well soluble in water and has an ionic crystal lattice.
4. (10 points) Two of the greenhouse gases which contribute to global warming are carbon dioxide (CO2)
and methane (CH4).
a. Name one other greenhouse gas. 1 point
b. Name one natural and one man-made source of carbon dioxide. 2 points
c. The diagram shows part of the Erath and ways that carbon dioxide can be removed from Earth’s
atmosphere. Give three ways that carbon dioxide can be removed from the Earth’s atmosphere. 3 points
d. Changes in ocean chemistry can have extensive direct and indirect effects on organisms and their
habitats, for example, the production of shells and plates out of calcium carbonate (CaCO3). Calculate the
amount of calcium carbonate which would be produced in 1 m3 15 °C of seawater if all dissolved CO2 would
be used. Consider that seawater density is 1 g/cm3. 4 points
5. (13 points) A mixture of petrol and air is burned in a car engine. Petrol is a mixture of alkanes –
compounds consisting of hydrogen and carbon atoms only. Air is a mixture of gases.
The tables give information about the composition of petrol and the composition of air.
Petrol
Compounds
hexane
heptane
octane
nonane
decane
Air
Gas
Percentage by volume (%)
nitrogen
78
oxygen
21
carbon dioxide
0.035
Small amounts of water and other
gases
Formula
C6H14
……
C8H18
C9H20
C10H22
a. According to information given in the petrol composition table write a molecular formula of heptane. 1
point
b. Compounds in petrol burn in air. The equations represent two reactions of hexane burning in air.
Reaction 1
Reaction 2
C6H14 + 9.5 O2
C6H14 + 6.5 O2
→
→
6 CO2 + 7 H2O
6 CO + 7 H2O
i) Give a reason why produced carbon compounds are different. 1 point
ii) Indicate oxidation states of both produced carbon oxides. 2 points
c. A 10 g mixture of hexane and decane was completely burnt and 15.57 l CO2 was produced. Write
balanced reactions equations and calculate the percentage composition of the initial mixture of alkanes.
How much air needed to completely burn this mixture? 9 points