‫ العادية‬8002 ‫دورة سنة‬
‫الشهادة المتوسطة‬
‫مسابقة في مادة الكيمياء‬
‫ ساعة واحدة‬:‫المدة‬
Part of
the Q
1
2
3
4.1
4.2
1
2
3
‫وزارة التربية والتعليم العالي‬
‫المديرية العامة للتربية‬
‫دائرة االمتحانات‬
‫معيار التصحيح‬
Answer
First Exercise (6 points)
Based on Figure-1, the bond in O2 molecule is a double covalent bond because it results
from the sharing of two pairs of electrons between two oxygen atoms.
The valence of oxygen atom is 2.
*The number of valence electrons for each oxygen atom is 6, its valence is 8-6 = 2
*Based on Lewis dot structure, oxygen atom has two unpaired electrons =>its valence is
2.
Based on Figure-1:
N has five valence electrons (Lewis dot structure) (0.5pt)
N belongs to period 2. The electron configuration of N is: K2, L5 (0.5pt)
The atom is electrically neutral. The number of protons is equal to the number of
electrons. (0.5pt)
Number of protons = Atomic number (Z)  Z = 7 (0.5pt)
Number of moles n = m (g) / M (g.mol–1) (0.5pt)
n (He) = 0.8/4 = 0.2mol (0.5pt)
*No unit (0.25pt)
Under high pressure (deep-diving), nitrogen gas is dissolved in the blood, where it can
cause mental disorientation. To avoid this disorientation, he filled his breathing bottle
with helium-oxygen mixture. The un-reactive helium gas which dissolves in the blood
does not cause mental disorientation.
*To avoid mental disorientation (zero)
Second Exercise (7 points)
- Cu strip is the anode of the galvanic cell (G2).
- In the galvanic cell (G2), metal Y has less tendency to lose electrons than Cu, because
Cu is releasing electrons. Based on the given axis "tendency to lose electrons",
Y is Ag.(1pt)
- In the galvanic cell (G1), metal X has more tendency to lose electrons than Cu, because
X is releasing electrons. Based on the given axis "tendency to lose electrons",
X is Zn. (1pt)
The materials numbered on the schema of the galvanic cell (G1) are:
1 - Solution containing Cu2+ ions
2 – Salt bridge
3 - Solution containing Zn2+ ions
4 - Connecting wires
5 – Voltmeter
(5×0.25 pt)
1
Mark
1
1
2
1
1
0.75
2
1.25
4
5
6
1.1
1.2
2.1
2.2
3.1
3.2
4
5
* - U tube containing electrolyte.
- Multimeter.
- The half-reaction at the anode is:
Cu → Cu2+ + 2e- The half-reaction at the cathode is:
Ag+ + e- → Ag (2×0.5 pt)
2+
Cu → Cu + 2e
2x (Ag+ + e- → Ag )
(0.5pt)
+
2+
Cu + 2Ag → Cu + 2 Ag (0.5pt) is the equation of the overall reaction of the
galvanic cell (G2) .
- The written cell representation which has the greater voltage is:
Zn | Zn2+ ― salt bridge ― Ag+ | Ag Because the difference in the tendency to lose
electrons between Zn and Ag is greater than the difference in the tendency to lose
electrons between Zn and Cu.
Third Exercise (7 points)
The molecular formula of ethanol is C2H6O
The condensed structural formula is:
CH3 – CH2 OH
Compound (B) is: Ethanoic acid.
C – OH, is simple covalent bond.
C = O, is double covalent bond. (2×0.50pt)
According to the law of conservation of mass (atoms), the number of atoms of each
element is conserved. (0.5pt)
A molecule of ethanol contains two carbon atoms =>A molecule of alkene (E) contains
two carbon atoms. The general formula of alkenes is: CnH2n.
For n = 2  The molecular formula of (E) is: C2H4 (1pt)
*CnH2n+H2O→ C2H6O for n=2 the formula is C2H4 (1 pt)
*CxHy+H2O→C2H6O for x= 2 and y+2 = 6 => y=4 the formula of (E) is C2H4 (1 pt)
*C2H4+H2O→C2H6O (1 pt)
The functional group is: Double covalent bond.
The equation of the reaction is:
H H
H H
‫׀ ׀‬
‫׀ ׀‬
H- C = C - H + H- Cl → H- C – C - H
‫׀ ׀‬
H Cl
*molecular formula or condensed structural formula (0.5pt)
Esterification reaction.
* Ester formation reaction.
2
1
1
1
1
0.50
0.75
1
1.5
0.50
1.25
0.50