Download First Exercise (7 points) Importance of the Element Phosphorus The

First Exercise (7 points)
Importance of the Element Phosphorus
The element phosphorus in the combined state has an important role in the human body. It is
essential for memory, for the formation and the maintenance in good health of the bones and of
the teeth. In industry, phosphorus is used to produce phosphoric acid H3 PO4 . Also, it it converted
to phosphorus sulfide (P4 S3 ) which is used as active ingredient in the match head.
Given: Relative charge of an electron=-1; M(P)= 31 g.mol-1
1- Give the value of the letters a, b and c in the table below.
Atomic symbol
31
15
Atomic number
Number of neutrons
Relative charge of the
electron cloud
c
a
b
P
2- The electron configuration of phosphorus atom is: K 2 , L8 , M5
2.1- Deduce the placement, column (group) and row (period) of phosphorus in the
periodic table.
2.2- Write the Lewis electron dot symbol of phosphorus atom.
3- Hydrogen atom has one electron on its valence energy level (K). The element hydrogen
combines with the element phosphorus to form the compound phosphine (PH3 ).
- Explain the bond formation in the molecule of phosphine.
4- The human body needs on the average 0.062g of phosphorus (P) per day.
4.1- Determin the number of moles of phosphorus corresponding to this mass.
4.2- Choose among the given number of moles of phosphorus the amount needed by
human body in seven days.
a- 0.148mol b- 0.14 mol
c- 0.014 mol
d- 1.48 mol
e- 1.5 mol
5- Give two reasons, based on the text, why humans should include in their daily nutrition,
food containing phosphorus.
6- Pick out from the passage one use of phosphorus in industry.
Second Exercise (7 points)
Organic Acids and Alcohols
Organic acids and alcohols are very common compounds
used in our everyday life. The bar graphs (I) and (II)
given on the right represent the number of C, O and H
atoms in a molecule of each of the two organic
compounds (A) and (B) respectively.
1- Choose among the molecular formulas given below,
the one that corresponds to compound (A) and the one
that corresponds to compound (B).
a- CH4 O b- C2 H4 O2
c- C2 H6 O
d- CH2 O 2
2- Compound (A) is an alcohol and compound (B) is carboxylic acid.
2.1- Write the condensed structural formula of compound (A) and the structural formula of
compound (B).
2.2- Given the IUPAC name of compound (B).
3- Indicate the type of bonds between the carbon atom and each of the two oxygen atoms of
the carboxyl group of compound (B).
4- One molecule of compound (A) can be obtained by the addition of one molecule of water
(hydration) to one molecule of hydrocarbon (W) in the presence of sulfuric acid as catalyst
and heat.
4.1- Determine the molecular formula CxHy of hydrocarbon (W).
4.2- Specify, based on this chemical property, the class (family) of hydrocarbon (W).
5- Food manufactures often use certain esters which are chemically prepared as artificial
flavoring agents in soft drinks to make it taste natural. Compound (A) reacts with compound
(B) to produce an organic compound (E) and water.
- Justify why compound (E) can be used as artificial flavoring agent by food manufactures.
Third Exercise (6points)
Voltage of Electrochemical Cells
Two galvanic cells (G1) and (G2) are constructed. The anode is the metal which has more
tendency to lose electrons than the cathode. The greater the difference between the tendency of
the metals to lose electrons, the greater is the voltage reading of the voltmeter. See the schemas
below.
1- Copy and complete the table given below.
Galvanic cell
Anode half - Cathode
Anode Oxidation halfReduction
cell
reaction
Half-reaction
(G1 )
Cu ‫ ׀‬Cu2+
Cu
Ag++e- →Ag
(G2 )
Cu
Al →3e- + Al3+
2- Based on the given and the schemas of the two galvanic cells:
2.1- Deduce which one of the metals Cu, Ag or Al has the least tendency to lose
electrons.
2.2- Indicate for which pair of metals (aluminium and copper) or (copper and silver), the
difference between the tendency to lose electrons is greater. Justify.
3- Show that the equation of the overall reaction of galvanic cell (G2) is:
2Al + 3Cu2+ → 2Al3+ + 3Cu
4- Give the written cell representation of galvanic cell (G1 ).