chemisrry unit 2 revision Qs

1. The diagram below shows the electronic structure of boron.

(a) The electrons are represented by arrows. What property of the electrons do these ‘up’ and ‘down’ arrows represent?
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(1) (b) Suggest why electrons which occupy the 2p sub-levels have a higher energy than electrons in the 2s sub-level.
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(1) (c) Complete the following energy level diagram to show the electronic structure of carbon. (2) (d) Explain the meaning of the term first ionisation energy.
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(2)

(e) Explain why boron has a lower first ionisation energy than beryllium.
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(3)

(f) Explain why the first ionisation energy of helium is very large.
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(1)
(Total 10 marks)

2. (a) Complete the table below to show the relative masses and charges of a proton, a neutron and an electron.

Relative mass
Relative charge
Proton

Electron

Neutron

(3) (b) Describe the process by which particles are ionised in a mass spectrometer.
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(2)

(c) Give two reasons why particles must be ionised before being analysed in a mass spectrometer.
Reason 1 .....................................................................................................................
Reason 2 .....................................................................................................................
(2)

(d) A sample of boron contains 20% by mass of 10B and 80% by mass of 11B.
Calculate the relative atomic mass of boron in this sample.
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(2) (e) Compound X contains only boron and hydrogen. The percentage by mass of boron in X is 81.2%. In the mass spectrum of X the peak at the largest value of m/z occurs at 54.
(i) Use the percentage by mass data to calculate the empirical formula of X.
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(ii) Deduce the molecular formula of X.
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(4)
(Total 13 marks)

3. (a) What is a covalent bond?
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(1)

(b) Draw diagrams to show the shapes of the following molecules and in each case show the value of the bond angle on the diagram.
BeCl2 BF3

CCl4 SF6

(8) (c) Explain why the shape of NF3 is not the same as the shape of BF3.
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(3)
(Total 12 marks)

4. (a) Explain why electrical conductivity decreases across Period 3 from sodium to phosphorus.
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(3)

(b) Explain why atomic radius decreases across Period 3 from sodium to chlorine.
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(2)

(c) The table below shows the melting temperatures, Tm, of the Period 3 elements.
Element
Na
Mg
Al
Si
P
S
Cl
Ar
Tm/K
371
923
933
1680
317
392
172
84
Explain the following in terms of structure and bonding.
(i) Magnesium has a higher melting temperature than sodium.
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(2)

(ii) Silicon has a very high melting temperature.
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(2)

(iii) Sulphur has a lower melting temperature than magnesium.
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(2)

(iv) Argon has a lower melting temperature than chlorine.
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(3)
(Total 14 marks)

5. Describe, with the aid of diagrams, the structure of, and bonding in, sodium chloride, iodine, diamond and graphite. How do the properties of these different types of crystal enable you to distinguish between them?
(Total 20 marks)

6. (a) Figure 1 shows the melting points of the elements sodium to argon.

Figure 1 By reference to their structure and bonding, explain the melting points of the elements from sodium to argon.
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(5)

(b) Figure 2 shows the trends in atomic radius and molar first ionisation energy for
Group 1 elements.

Figure 2 Explain why the atomic radius increases and the ionisation energy decreases as the group is descended.
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(4) (c) Write balanced equations to show the reaction of water with:
(i) sodium;
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(1)
(ii) sodium oxide.
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(1)
(Total 11 marks)

7. (a) Give the symbol, including mass number and atomic number, for the isotope which has a mass number of 34 and which has 18 neutrons in each nucleus
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(2)

(b) Give the electronic configuration of the F– ion in terms of levels and sub-levels.
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(1)
(c) Give a reason why it is unlikely that an F– ion would reach the detector in a mass spectrometer.
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(1)
(d) Some data obtained from the mass spectrum of a sample of carbon are given below.
Ion
12C+
13C+
Absolute mass of one ion/g
1.993 × 10–23
2.158 × 10–23
Relative abundance/%
98.9
1.1 Use these data to calculate a value for the mass of one neutron, the relative atomic mass of 13 C and the relative atomic mass of carbon in the sample.
You may neglect the mass of an electron. Mass of one neutron. ..................................................................................................
Relative atomic mass of 13C. .......................................................................................
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..................................................................................................................................... Relative atomic mass of carbon in the sample............................................................
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(6)
(Total 10 marks)

8. The boiling temperatures, Tb, of some Group IV and Group V hydrides are given below
Compound
CH4
SiH4
NH3
PH3
Tb/K
112
161
240
185 (a) The polarity of a carbon-hydrogen bond can be shown as —
(i) What does the symbol d+, above the hydrogen atom, signify?
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(ii) Explain briefly, in terms of its shape, why a CH4 molecule has no overall polarity.
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(3)

(b) Name the type of intermolecular forces which exist between CH4 molecules in liquid methane.
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(1) (c) Explain why the boiling temperature of PH3 is greater than that of CH4.
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(3) (d) Explain why the boiling temperature of NH3 is greater than that of PH3
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(2)

(e) Sketch a diagram to show the shape of a molecule of NH3 and indicate on your diagram how this molecule is attracted to another NH3 molecule in liquid ammonia.

(3) (f) Suggest why the strength of the C–H bond in CH4 is greater than that of the Si–H bond in SiH4. State the relationship, if any, between the strength of the covalent bond in CH4 and the boiling temperature of CH4
Reason for stronger C-H bond....................................................................................
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Relationship between covalent bond strength and boiling temperature.....................
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(2)
(Total 14 marks)

9. (a) Compound A (Mr = 215.8) contains 22.24% carbon, 3.71% hydrogen and 74.05% bromine by mass. Show that the molecular formula of A is C4H8Br2.

(3)

(b) There are nine structural isomers of molecular formula C4H8Br2, three of which have branched carbon chains. Give the names and draw the graphical formulae for any two of the branched chain isomers of C4H8Br2.
Name of isomer 1 .......................................................................................................
Graphical formula of isomer 1

Name of isomer 2 .......................................................................................................
Graphical formula of isomer 2

(4) (c) 2-bromopropane, CH3CH(Br)CH3, will react with KOH to form two different products.
One product is formed by an elimination reaction, while the other is formed by a substitution reaction. For each type of reaction, suggest the condition(s) most likely to lead to that type of reaction and draw the structure of the organic product.
(i) Elimination reaction
Condition(s) .....................................................................................................
Structure of the product

(2)

(ii) Substitution reaction
Condition(s) .....................................................................................................
Structure of the product

(2) (d) For the reaction between 2-bromopropane and potassium cyanide:
(i) give the name or formula of the attacking species involved;
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(1)
(ii) give the name of the mechanism involved;
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(1) (iii) write an equation for the reaction;
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(1)
(iv) draw the graphical structure of the organic product.

(1)
(Total 15 marks)

10. (a) Co-ordinate bonding can be described as dative covalency. In this context, what is the meaning of each of the terms covalency and dative?
Covalency....................................................................................................................
Dative .........................................................................................................................
(2)

(b) Write an equation for a reaction in which a co-ordinate bond is formed.
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(2) (c) Why is sodium chloride ionic rather than covalent?
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(2) (d) Why is aluminium chloride covalent rather than ionic?
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(2)

(e) Why is molten sodium chloride a good conductor of electricity?
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(1)
(f) Explain, in terms of covalent bonding, why the element iodine exists as simple molecules whereas the element carbon does not.
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(3)
(Total 12 marks)

11. The diagram below shows how a water molecule interacts with a hydrogen fluoride molecule.

(a) What is the value of the bond angle in a single molecule of water?
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(1) (b) Explain your answer to part (a) by using the concept of electron pair repulsion.
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(4)

(c) Name the type of interaction between a water molecule and a hydrogen fluoride molecule shown in the diagram above.
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(1) (d) Explain the origin of the d+ charge shown on the hydrogen atom in the diagram.
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(2)

(e) When water interacts with hydrogen fluoride, the value of the bond angle in water changes slightly. Predict how the angle is different from that in a single molecule of water and explain your answer.
Prediction ...................................................................................................................
Explanation ................................................................................................................
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(2)
(Total 10 marks)