Download AS Paper 1 Practice Paper 12 - A

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AS LEVEL CHEMISTRY
PAPER 1
PRACTICE PAPER 12
(structured questions only)
Answer all questions
Max 80 marks
Name
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Mark
……../80
……....%
Grade ………
Note – this paper only contains structured questions
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1.
Nitrogen dioxide dissociates according to the following equation.
2NO2(g)
2NO(g) + O2(g)
When 21.3 g of nitrogen dioxide were heated to a constant temperature, T, in a flask of volume
11.5 dm3, an equilibrium mixture was formed which contained 7.04 g of oxygen.
(a)
(i)
Calculate the number of moles of oxygen present in this equilibrium mixture and
deduce the number of moles of nitrogen monoxide also present in this equilibrium
mixture.
Number of moles Of O2 at equilibrium .................................................
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Number of moles of NO at equilibrium .................................................
(ii)
Calculate the number of moles in the original 21.3 g of nitrogen dioxide and hence
calculate the number of moles of nitrogen dioxide present in this equilibrium mixture.
Original number of moles of NO2 ................................................................
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Number of moles of NO2 at equilibrium ...............................................
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(4)
(b)
Write an expression for the equilibrium constant, Kc, for this reaction. Calculate the value
of this constant at temperature T and give its units.
Expression for Kc ..........................................................................................
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Calculation ....................................................................................................
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(4)
(c)
The total number of moles of gas in the flask is 0.683. Use the ideal gas equation to
determine the temperature T at which the total pressure in the flask is 3.30 × 105 Pa.
(The gas constant R = 8.31 J K–1mol–1)
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(3)
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(d)
State the effect on the equilibrium yield of oxygen and on the value of Kc when the same
mass of nitrogen dioxide is heated to the same temperature T, but in a different flask of
greater volume.
Yield of oxygen .............................................................................................
Value of Kc ....................................................................................................
(2)
(Total 13 marks)
2.
The equation below shows the reaction between boron trifluoride and a fluoride ion.
BF3 + F– → BF
(i)
Draw diagrams to show the shape of the BF3 molecule and the shape of the BF
each case, name the shape. Account for the shape of the BF
angle present.
ion. In
ion and state the bond
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(ii)
In terms of the electrons involved, explain how the bond between the BF3 molecule and
the F– ion is formed. Name the type of bond formed in this reaction.
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(Total 9 marks)
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3.
Water can be found as ice, water and steam.
(a)
The following diagram shows the arrangement of some of the water molecules in a
crystal of ice.
With reference to the structure shown above give one reason why ice is less dense than
water.
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(1)
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(b)
Water and methane have similar relative molecular masses and both contain the element
hydrogen. The table below gives some information about water and methane.
H2O
CH4
Mr
18.0
16.0
Melting point / K
273
91
(i)
State the strongest type of intermolecular force holding the water molecules
together in the ice crystal.
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(1)
(ii)
State the strongest type of intermolecular force in methane.
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(1)
(iii)
Give one reason why the melting point of ice is higher than the melting point of
methane.
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(1)
(c)
A molecule of H2O can react with an H+ ion to form an H3O+ ion.
(i)
Draw and name the shape of the H3O+ ion. Include any lone pairs of electrons.
Shape of the H3O+ ion
Name of shape ...................................................................................
(2)
(ii)
Suggest a value for the bond angle in the H3O+ ion.
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(1)
(iii)
Identify one molecule with the same number of atoms, the same number of
electrons and the same shape as the H3O+ ion.
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(1)
(d)
Water can also form the hydroxide ion.
State the number of lone pairs of electrons in the hydroxide ion.
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(1)
(Total 9 marks)
Paddington Academy
4.
Barium can be extracted from barium oxide (BaO) in a process using aluminium.
A mixture of powdered barium oxide and powdered aluminium is heated strongly.
The equation for this extraction process is shown below.
3BaO(s) + 2Al(s) → 3Ba(s) + Al2O3(s)
Some standard enthalpies of formation are given in the table below.
Substance
∆H
(a)
(i)
f
ο
/ kJ mol–1
BaO(s)
Al2O3(s)
–558
–1669
State what is meant by the term standard enthalpy of formation.
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(3)
(ii)
State why the standard enthalpy of formation of barium and that of aluminium are
both zero.
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(1)
(iii)
Use the data to calculate the standard enthalpy change for the reaction shown by
the equation above.
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(3)
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(c)
(i)
Write an equation for the reaction of barium with water.
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(1)
(ii)
A solution containing barium ions can be used to test for the presence of sulfate
ions in an aqueous solution of sodium sulfate.
Write the simplest ionic equation for the reaction which occurs and state what is
observed.
Simplest ionic equation
.............................................................................................................
Observation .........................................................................................
(2)
(iii)
State how barium sulfate can be used in medicine. Explain why this use is possible,
given that solutions containing barium ions are poisonous.
Use .....................................................................................................
Explanation .........................................................................................
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(2)
(Total 12 marks)
5.
Acidified silver nitrate solution can be used to identify and distinguish between halide ions in
solution.
(a)
Explain why hydrochloric acid should not be used to acidify the silver nitrate.
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(1)
(b)
State and explain what would be observed when acidified silver nitrate solution is added
to a solution of sodium fluoride.
Observation .................................................................................................
Explanation …..............................................................................................
(2)
(c)
State what would be observed when acidified silver nitrate solution is added to a solution
containing iodide ions. Write the simplest ionic equation for the reaction that occurs.
Observation .................................................................................................
Explanation ..................................................................................................
(2)
(Total 5 marks)
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6.
In the past 150 years, three different processes have been used to extract bromine from
potassium bromide. These processes are illustrated below.
Extraction Process 1
2KBr + MnO2 + 2H2SO4 → MnSO4 + K2SO4 + 2H2O + Br2
Extraction Process 2
The reaction of solid potassium bromide with concentrated sulfuric acid.
Extraction Process 3
The reaction of aqueous potassium bromide with chlorine gas.
(a)
Write a half-equation for the conversion of MnO2 in acid solution into Mn2+ ions and water.
In terms of electrons, state what is meant by the term oxidising agent and identify the
oxidising agent in the overall reaction.
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(3)
(b)
Write an equation for Extraction Process 2 and an equation for Extraction Process 3.
Calculate the percentage atom economy for the extraction of bromine from potassium
bromide by Extraction Process 3. Suggest why Extraction Process 3 is the method in
large-scale use today.
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(5)
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(c)
Bromine has been used for more than 70 years to treat the water in swimming pools.
The following equilibrium is established when bromine is added to water.
Br2 +
H2O
HBrO + HBr
Give the oxidation state of bromine in HBr and in HBrO
Deduce what will happen to this equilibrium as the HBrO reacts with micro-organisms in
the swimming pool water. Explain your answer.
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(4)
(Total 12 marks)
7.
(a)
Sodium hydroxide can be obtained as a monohydrate (NaOH.H2O). When heated, the
water of crystallisation is lost, leaving anhydrous sodium hydroxide (NaOH).
A chemist weighed a clean, dry crucible. The chemist transferred 1.10 g of NaOH.H2O to
the crucible. The crucible and its contents were heated until a constant mass had been
reached. The chemist recorded this mass.
The experiment was repeated using different masses of the monohydrate.
For each experiment, the chemist recorded the original mass of NaOH.H2O and the mass
of NaOH left after heating. The chemist’s results are shown in the table below.
Mass of NaOH.H2O / g
Mass of NaOH / g
0.50
0.48
1.10
0.79
2.05
1.41
2.95
2.06
3.50
2.28
4.20
2.93
4.90
3.41
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(i)
Plot a graph of mass of NaOH.H2O (y-axis) against mass of NaOH on the grid.
Draw a straight line of best fit on the graph.
(3)
(ii)
Use your graph to determine the mass of NaOH.H2O needed to form 1.00 g of
NaOH
........................... g
(1)
Paddington Academy
(iii)
Use your answer from part (a) (ii) to confirm that the formula of sodium hydroxide
monohydrate is NaOH.H2O
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(2)
(b)
Sodium hydroxide is used to remove grease from metal components.
Sodium hydroxide cannot be used to clean components made of aluminium because it
reacts with this metal.
(i)
Balance the equation for the reaction of aqueous sodium hydroxide with aluminium.
...... NaOH + ...... Al + ...... H2O
...... NaAl(OH)4 + 3H2
(1)
(ii)
In 1986, a sealed aluminium tank exploded while being used by mistake for
transporting concentrated sodium hydroxide solution.
Suggest one reason why the tank exploded.
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(1)
(c)
A strong alkali such as potassium hydroxide is used as the electrolyte in some alkaline
batteries for household use. The electrolyte will escape if the battery casing is broken.
Suggest one reason why a leak of this electrolyte is hazardous.
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(1)
(Total 9 marks)
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8.
Copper(II) sulfate solution, together with copper(II) carbonate (CuCO3) powder, can be used to
determine the identity of three solutions A, B and C. The three solutions are known to be
hydrochloric acid, barium chloride, and sodium chloride.
In Experiment 1 a small amount of copper(II) carbonate powder was added to each of the three
solutions.
In Experiment 2 a dropping pipette was used to add 2 cm3 of copper(II) sulfate solution to each
of the three solutions.
The results of these experiments are shown in the table below.
(a)
Experiment 1
Addition of copper(II)
carbonate powder
Experiment 2
Addition of copper(II)
sulfate solution
Solution A
no visible change
white precipitate
Solution B
no visible change
no visible change
Solution C
effervescence
(bubbles of gas)
no visible change
Use the observations in the table to deduce which of the solutions, A, B or C is
hydrochloric acid ............................................................................................
barium chloride ..............................................................................................
(2)
(b)
Explain why a precipitate was formed when copper(II) sulfate solution was added to
solution A.
Write an equation for the reaction that occurred.
Explanation ....................................................................................................
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Equation .........................................................................................................
(2)
(c)
Suggest the identity for the colourless gas produced when copper(II) carbonate powder
was added to solution C.
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(1)
Paddington Academy
(d)
Identify the two reagents that could be used in a test to confirm that the solutions
contained chloride ions, not bromide ions. State what would be observed on addition of
each reagent.
Reagent 1 ......................................................................................................
Observation 1 .................................................................................................
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Reagent 2 ......................................................................................................
Observation 2 .................................................................................................
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(4)
(e)
Copper(II) sulfate is toxic. Suggest one safety precaution you would take to minimise this
hazard when wiping up a spillage of copper(II) sulfate solution.
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(1)
(Total 10 marks)
9.
During a titration a chemist may rinse the inside of the conical flask with distilled or deionised
water. The water used for rinsing remains in the conical flask.
(a)
Explain why this rinsing can improve the accuracy of the end-point.
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(1)
(b)
Explain why the addition of water during rinsing does not give an incorrect result.
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(1)
(Total 2 marks)
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10.
In an experiment to determine the concentration of a solution of sodium hydroxide, 25.0 cm3 of
0.100 mol dm–3 hydrochloric acid were transferred to a conical flask. An indicator was added to
the flask. The solution of sodium hydroxide was then added to the flask from a burette.
(a)
State a suitable amount of indicator solution that should be added to the flask.
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(1)
(b)
State why it is important to fill the space below the tap in the burette with alkali before
beginning the titration.
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(1)
(Total 2 marks)