First Exercise (7points)
Calcium Ion Is Essential for Health
The calcium ion is essential for the formation and maintenance of teeth, bones and other tissues in
the human body. The deficiency of calcium ion causes a disease called osteoporosis. The bar graph
shows the mass number of calcium and oxygen atoms.
1- Determine, using the information given in the bar
graph, the number of neutrons for the oxygen atom.
2- The electron configuration for each of oxygen atom
and calcium atom, respectively is:
O: K2 L6
and Ca: K2 L8 M8 N2
a- Identify the placement, row (period) and
column (group), of calcium atom in the periodic
table.
b- Write the Lewis electron – dot symbol for each
of the mentioned atoms.
3- A calcium atom loses two electrons to attain a stable
electron configuration and a calcium ion having a
2+ charge is obtained.
a- Translate this statement into an equation form.
b- Justify, by calculation, why the calcium ion has
a 2+ charge.
Relative charge of a proton is 1+ and relative charge of an electron is 14- The physician recommends to a patient suffering from osteoporosis a certain medicament.
Justify what metal-ion should this medicament contain.
Second Exercise (6 points)
Oxygen Is an Important Gas
Oxygen gas is essential for life processes such as respiration in the cells of living things and it is
needed for burning.
In the laboratory, oxygen gas can be obtained by applying
electrolysis on water to which a small quantity of sulfuric acid is
added. The adjacent schema shows the different parts of the
setup used for this electrolysis.
The electrodes used are inert.
The half - reaction that takes place at the anode is:
2H2O → 4H+ + O2 + 4e- (I)
The half- reaction that takes place at the cathode is:
2H+ +2e- → H2 (II)
1- Deduce the over -all reaction of this electrolysis.
2- Based on what has preceded, attribute to each numbered part of the schema the
corresponding term from the following list: anode, electrolytic cell, direct current power
supply, hydrogen gas, oxygen gas.
Given: Number 3 is cathode.
3- Extract from the passage, the two sentences that show the importance of oxygen gas.
4- The Lewis electron – dot symbol for each of hydrogen and oxygen atom, respectively, is: H
and O Explain why a water molecule (H2O) consists of one oxygen atom and two hydrogen
atoms.
Third Exercise (7 points)
Hydrocarbons and Enviroment
At the refinery, petroleum is separated into different fractions (groups of hydrocarbons that have
different boiling points). The separation of the hydrocarbons takes place in a fractionating column.
1- Give the name of the separation method employed.
2- The carbon atoms in the molecule of an alkane obtained from petroleum could be in a
straight – chain or a branched – chain. (F) and (G) are among the condensed structural
formulas of the alkane having molecular formula, C7H16.
(F) CH3-CH2-CH2-CH2-CH2-CH2-CH3 and CH3-CH2-CH-CH3
Indicate which of the condensed sutructural formulas (F) or (G) is branched – chain and
give the (IUPAC) name of the corresponding hydrocarbon.
3- After separating the alkanes, ethene (C2H4) could be obtained by cracking of alkanes having
long chain of carbon atoms.
- Distinguish between fractional distillation and cracking.
4- The ethane obtained is used in industry to produce chloroethane and ethanol.
- Write, using condensed structural formulas, the equation of the reaction that allows to
produces each of the mentioned chemicals.
5- Ethene undergoes polymerization reaction to produce polyethene (polyethylene). Polyethene
is used to manufacture drinking water bottles.
a- Write, using structural formulas, the equation of the polymerization reaction and identify
the type of this reaction.
b- The incineration (burning) of drinking water polyethene-bottles that are thrown away
increases the amount of greenhouse gases such as carbon dioxide and water vapor into
the atmosphere.
- Indicate the effect of the increase of the amount of greenhouse gases on the Earth’s
atmospheric temperature and give one of the consequences.
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