Class
Adm No
Candidate Name:
2021 Weighted Assessment 2
Pre-University 1
H2 CHEMISTRY
9729
Multiple-Choice & Structured Questions
28 July 2021
1 hour 15 minutes
Candidates answer on the Question paper.
Additional materials: Data Booklet
READ THESE INSTRUCTIONS FIRST
Do not turn over this question paper until you are told to do so.
Write your name, class on all the work you hand in.
Write in dark blue or black pen.
You may use an HB pencil for any diagrams or graphs.
Do not use staples, paper clips, glue or correction fluid.
Answer all questions.
All numerical answers should be given to 3 significant figures, and units must be given where
appropriate.
The use of an approved scientific calculator is expected, where appropriate.
A Data Booklet is provided.
At the end of the examination, fasten all your work securely together.
The number of marks is given in brackets [ ] at the end of each question or part question.
Question
MCQ
10
11
12
13
Total
Marks
9
7
8
9
7
This question paper consists of 8 printed pages and 2 blank pages.
40
2
Section A – Multiple Choice
For each question there are four possible answers, A, B, C, and D. Choose the one you consider to
be correct and fill in your answers to Section A in the boxes below.
1
Q1
Q2
Q3
Q4
Q6
Q7
Q8
Q9
Q5
When passed through an electric field, the 1H+ ion is deflected as shown below.
A
1
H+
−
B
o
4
o
4
C
source
D
+
Which of the above beams represents the deflection for an ion 2X2– when passed through the
same electric field?
2
Use of the Data Booklet is relevant to this question.
Which of the following species has the same electronic configuration as Mn+?
3
A
Cr
B
Cu
C
Fe2+
D
V+
In which of the following pairs is the bond angle in the first species smaller than that in the
second species?
1
PBr3, PBr4+
2
H2Se, H2O
3
SF2, SCl2
A
1 and 2 only
B
1 and 3 only
C
2 and 3 only
D
1, 2 and 3
3
4
The successive ionisation energies, in kJ mol–1, of elements G and H are given below.
G
H
580
940
1820
2050
2740
2970
11600
4140
14800
6590
18400
7880
23300
14900
Which statements about elements G and H are true?
1
The first ionisation energy of G is lower than that of the element preceding it in the Periodic
Table.
5
2
G and H forms a compound with the formula G3H2.
3
H has an outer electronic configuration ns2 np4.
A
1 and 2 only
B
C
1 and 3 only
2 and 3 only
D
1, 2 and 3
Propanone is known commonly as acetone and is used as a nail polish remover.
How many σ and π bonds are there in the molecule?
6
σ bonds
π bonds
A
8
1
B
8
2
C
9
1
D
9
2
40 cm3 of an unknown hydrocarbon, CxHy, was exploded in 280 cm3 oxygen. The volume of the
residual gases was found to be 200 cm3. On being shaken with potassium hydroxide, the final
volume was found to be 80 cm3.
What is the molecular formula of the unknown hydrocarbon?
(All volumes are measured at r.t.p)
A
C2H4
B
C2H6
C
C3H6
D
C3H8
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4
7
Use of the Data Booklet is relevant to this question.
An element M can exist in a few oxidation states.
15.00 cm3 of an aqueous solution of 0.100 mol dm3 of Mn+ required 20.00 cm3 of
0.0250 mol dm3 of acidified K2Cr2O7 solution for a complete reaction.
What is the change in oxidation state of M?
A
8
+2
B
C
+3
D
-2
-3
The bond lengths and bond angles in the molecules of methane, ammonia and water may be
represented as follow:
ammonia
methane
C
109.5°
0.109 nm
water
0.101 nm
N
O
0.096 nm
105°
107°
What causes this trend in the bond angles shown?
1
Increasing repulsion between hydrogen atoms as the bond length decreases.
2
Number of non–bonding electron pairs of the central atom in the molecule.
3
Non-bonding electron pair–bonding electron pair repulsion is greater than bonding
electron pair–bonding electron pair repulsion.
A
3 only
B
1 and 2 only
C
2 and 3 only
D
1, 2 and 3
5
9
Trichloroisocyanuric acid is commonly used in swimming pools as a disinfectant. The
recommended concentration level of the acid is 1.50 mg per dm3 of water.
trichloroisocyanuric acid
Mr = 232.5
How many chlorine atoms are present in a 2.50 x 106 dm3 Olympic–sized swimming pool filled
with the recommended concentration level of trichloroisocyanuric acid?
A
2.91 x 1025
B
2.91 x 1028
C
9.71 x 1024
D
9.71 x 1027
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6
Section B: Structured Questions
Answer all questions.
10 The graph below shows the first ionisation energy of the elements beryllium to magnesium.
First ionisation energy / kJ mol-1
3000
2000
1000
0
Be
Be
(a)
Be
B
C
C
N
N
O
O
F
F
Ne
Ne
Na
Na
Mg
Mg
Define, with the aid of an equation, the term first ionisation energy of sodium.
…………………………………………………………………………………………………………
…………………………………………………………………………………………………………
…………………………………………………………………………………………………………
…………………………………………………………………………………………………….. [2]
(b)
Account for the general increasing trend of ionisation energy from beryllium to neon.
…………………………………………………………………………………………………………
…………………………………………………………………………………………………………
…………………………………………………………………………………………………………
…………………………………………………………………………………………………………
…………………………………………………………………………………………………….. [2]
For
Examiners’
Use
7
(c)
Explain why the first ionisation energy decreases from beryllium to boron and from nitrogen
to oxygen.
…………………………………………………………………………………………………………
…………………………………………………………………………………………………………
…………………………………………………………………………………………………………
…………………………………………………………………………………………………………
…………………………………………………………………………………………………….. [2]
(d)
Explain why the first ionisation energy decreases sharply from neon to sodium.
…………………………………………………………………………………………………………
…………………………………………………………………………………………………………
…………………………………………………………………………………………………….. [1]
[Total: 7]
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For
Examiners’
Use
8
11 Group 2 metals are commonly known as alkali earth metals as they generally dissolve in water to
form alkaline solutions. Magnesium and calcium are both group 2 metals.
(a)
Complete the table below for two isotopic species of magnesium.
isotopic species
[2]
number of neutrons
number of electrons
14
12
24
Mg2+
(b)
State the structure and bonding in magnesium.
Draw a labelled diagram to illustrate the structure of magnesium.
…………………………………………………………………………………………………………
…………………………………………………………………………………………………….. [3]
(c)
Predict how the melting point of magnesium will differ from beryllium. Explain.
…………………………………………………………………………………………………………
…………………………………………………………………………………………………………
…………………………………………………………………………………………………………
…………………………………………………………………………………………………………
…………………………………………………………………………………………………………
…………………………………………………………………………………………………….. [3]
[Total: 8]
For
Examiners’
Use
9
12 Magnesium oxide has a melting point of 2852 C.
(a)
For
Examiners’
Use
Explain, in terms of structure and bonding, why magnesium oxide has a higher melting point
than sodium oxide, which has a melting point of 1950 °C.
…………………………………………………………………………………………………………
…………………………………………………………………………………………………………
…………………………………………………………………………………………………………
…………………………………………………………………………………………………………
…………………………………………………………………………………………………………
…………………………………………………………………………………………………….. [3]
(b)
Draw the ‘dot-and-cross’ diagrams for magnesium oxide, and for water.
[2]
(c)
Magnesium ions in the aqueous state exists as the hydrate magnesium ion [Mg(H2O)6]2+,
where a central magnesium ion is bonded to six water molecules via dative covalent bonds.
(i) By considering the number of bond pairs and lone pairs of electrons around the central
magnesium ion, deduce the shape and bond angle about the central magnesium ion in
[Mg(H2O)6]2+.
Shape: ………………………………………
Bond Angle: …………………………… [2]
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10
(ii) Explain why the magnesium ion is able to form dative covalent bonds with water
molecules.
……………………………………………………………………………………………………
……………………………………………………………………………………………………
……………………………………………………………………………………………………
……………………………………………………………………………………………….. [2]
[Total: 9]
For
Examiners’
Use
11
13 To facilitate better plant growth, there is widespread use of fertilisers and soil additives in the
agricultural sector.
Agricultural lime is a soil additive used to increase soil pH so as to facilitate uptake of plant nutrients
such as nitrogen and phosphorous. It is usually made up of a combination of calcium carbonate
and magnesium carbonate.
A manufacturer claims that a 2.00 g sample of agricultural lime contains 92 % calcium carbonate
(Mr = 100.1) and 8 % magnesium carbonate (Mr = 84.3) by mass.
To verify the manufacturer’s claim, the following steps were carried out:
Step 1
The solid carbonate mixture was dissolved in 250 cm3 of
0.25 mol dm–3 hydrochloric acid.
Step 2
A 25.0 cm3 portion of this resultant solution was titrated with
0.14 mol dm–3 potassium hydroxide.
It was found that 12.50 cm3 of potassium hydroxide was
required for complete neutralisation.
(a)
(i) Use the information above to calculate the amount of HCl in the 25.0 cm3 portion that
reacted with potassium hydroxide in step 2.
[1]
(ii) Calculate the amount of excess HCl in the 250 cm3 volumetric flask in step 1.
[1]
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For
Examiners’
Use
12
(iii) Calculate the amount of HCl that has reacted with the solid carbonate in step 1.
[1]
(iv) Hence calculate the total amount of carbonate present in the sample.
[1]
(b)
Based on the manufacturer’s claim of
92% calcium carbonate and
8% magnesium carbonate by mass, calculate the amount of each carbonate present in the
sample of agricultural lime.
[2]
13
The manufacturer’s claim is considered valid if the difference between the actual and
theoretical total amount of carbonate present in the sample is less than 0.0010 mol.
(c)
Using your answers in (a)(iv) and (b), determine if the manufacturer’s claim is valid.
[1]
[Total: 7]
End of Weighted Assessment
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