Name:
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Date:
F.5 Chemistry Test 1 Microscopic World II
Time allowed : 30 minutes
September 2019
Section I – Multiple choice questions
(8 marks)
1
Which of the following combinations about the numbers of electron pairs in the outermost
shell of the phosphorous atom in a PCl5 molecule is correct?
Number of bond pair(s)
Number of lone pair(s)
A
5
0
B
4
1
C
3
2
D
2
3
2
In which of the following paris do the molecules have a similar shape?
A BF3 and NH3 B CS2 and OF2 C H2O and CO2 D SiH4 and CCl4
3
Which of the following statements about ammonia and phosphine (PH3) is correct?
A Ammonia molecule and phosphine molecule have a similar shape.
B Hydrogen bonds exist in both ammonia and phosphine.
C The boiling point of phosphine is higher than that of ammonia.
D Phosphine molecules are polar while ammonia molecules are non-polar.
4
Which of the following molecules would NOT form hydrogen bond with another of its own
molecule?
5
To which of the following molecule is the ‘octet rule’ applicable?
(1) CO2 (2) NO2 (3) SF2
A (1) and (2) only
(3)
6
B
(1) and (3) only
C
(2) and (3) only
D
Which of the following molecules is / are polar?
(1) CO
(2) CO2
(3) ClBr
A
(1) only B
(2) only C
(1) and (3) only
1
D
(2) and (3) only
(1), (2) and
Directions: Each question (Question 7 – 8) consists of two separate statements. Decide whether
each of the two statements is true of false; if both are true, then decide whether or not
the second statement is a correct explanation of the first statement. Then select one
option from A to D according to the following table:
A
B
C
D
Both statements are true and the 2nd statement is a correct explanation of the 1st statement.
Both statements are true but the 2nd statement is NOT a correct explanation of the 1st
statement.
The 1st statement is false but the 2nd statement is true.
Both statements are false.
1st statement
2nd statement
7
Methane can dissolve in water.
Methane can form hydrogen bonds with
water.
8
A sulphur hexafluoride molecule has a net
dipole moment.
Each S–F bond in a sulphur hexafluoride
molecule is polar.
9
a)
Sketch the boiling point trend of hydrogen halides (HF, HCl and HBr).
(2 marks)
b)
Explain your answer for (a).
(5 marks)
2
10
A jet of methanol (CH3OH) is run from a burette as shown below.
a) A positively charged rod is placed near to the jet of methanol as shown below.
Complete the above diagrams to show the expected observations. With reference to the
structure of a methanol molecule, explain your answers.
(2 marks)
b)
Explain whether the viscosity of methanol is higher or lower than that of ethanol
(CH3CH2OH).
(2 marks)
11. Both BF3 and NH3 exist as simple molecules.
(a) For each of these molecules, draw its three-dimensional structure. BF3 and NH3
(b) For each of these molecules, explain whether or not it is polar.
3
(2 marks)
(2 marks)
(c)
BF3 reacts with NH3 to give F3BNH3. Describe the bond formation between BF3 and NH3.
(2 marks)
12. Chlorine reacts with water according to the equation below:
Cl2(aq) + H2O(l)
HOCl(aq) + HCl(aq)
(a) Name the type of reaction involved.
(1 mark)
(b) (i) Complete the electron diagram below for a HOCl molecule.
Show the outermost shell electrons only.
(1 mark)
(ii) Predict the shape of a HOCl molecule. Explain your answer.
(1 mark)
(c) Chlorine has been added to drinking water for over a century. Recently, some
scientists have put forward the case of NOT chlorinating drinking water. This is
because chlorine may react with organic compounds in water to form CHCl3.
(i) Draw an electron diagram to represent the bonding in a CHCl3 molecule.
Show electrons in the outermost shells only.
(1 mark)
(ii) Draw the shape you expect for the CHCl3 molecule.
(i)
(ii)
4
(1 mark)
END
Suggested Answers
Section I – Multiple choice questions
(8 marks)
1
A
2
D
3
A
6
C
7
D
8
C
4
B
5
Section II – Short questions
9
(24 marks)
a)
b)
B
(2)
The boiling point of a compound depends on the strength of its intermolecular
attractions.
(1)
Hydrogen bonds exist in HF
while only van der Waals’ forces exist in HCl and HBr.
(1)
Hydrogen bonds are stronger than van der Waals’ forces.
More heat is needed to separate the HF molecules during boiling.
Thus, the boiling point of HF is higher than that of HCl.
(1)
A HBr molecule has a larger molecular size than a HCl molecule.
Hence the strength of van der Waals’ forces in HBr is greater than that in HCl.
(1)
(1)
More heat is needed to separate the HBr molecules during boiling.
Thus, the boiling point of HBr is higher than that of HCl.
5
10
a)
(1)
The methanol molecule is polar.
The jet of methanol is deflected by the positively charged rod.
b)
Negative ends of the molecules are attracted towards the rod.
The jet of methanol is also deflected by the negatively charged rod.
(1)
The viscosity of methanol is lower than that of ethanol.
(1)
Compared with ethanol, methanol has a smaller molecular size. The van der Waals’
forces in methanol is less strong.
(1)
11
12
a)
b)
Disproportionation /Redox
i)
(1)
(1)
6
ii)
c)
i)
V-shaped, the two bond pairs and two lone pairs repel each other.
(1)
ii)
(1)
7
(1)