CGP EXAM QUESTIONS: DF Flashcards
10g of calcium carbonate react with excess dilute hydrochloric acid at RTP to produce calcium chloride, water and carbon dioxide: CaCO3(s) + 2HCl(aq) –> CaCl2(s) + H2O(l) + CO2(g)
What volume of carbon dioxide gas is given off?
Mr of CaCO3 = 40.1 + 12.0 + (3 x 16.0) = 100.1
So 10g of calcium carbonate is (100.1/10) = 0.10 mol
From the equation, 1 mol of CaCO3, reacting with excess HCl, will produce 1 mol of CO2, so 0.10 mol of CaCO3 will produce 0.10 mol of CO2
At RTP, 0.10 mol of gas has a volume of 0.10 x 24.0 = 2.4 dm3
4 dm3 of ethane (C2H6) are burned in 20 dm3 of oxygen to produce carbon dioxide and water vapour.
Write a balanced equation for the reaction.
2C2H6 + 7O2 –> 4CO2 + 6H2O
or C2H6 + 3½O2 –> 2CO2 + 3H2O
4 dm3 of ethane (C2H6) are burned in 20 dm3 of oxygen to produce carbon dioxide and water vapour.
What is the total volume (at constant temperature and pressure) of all species present once the reaction is complete?
A) 20 dm3
B) 24 dm3
C) 26 dm3
D) 30 dm3
C) 26 dm3
6dm3 of unreacted O2, 8 dm3 of CO2 and 12 dm3 of H2O
Magnesium carbonate (MgCO3) thermally decomposes to produce magnesium oxide (MgO) and carbon dioxide. What mass of magnesium carbonate is needed to produce 6.00 dm3 of carbon dioxide at RTP?
MgCO3 –> MgO + CO2
1 mole of MgCO3 produces 1 mole of CO2
At RTP, 6.00 dm3 of CO2 = 6.00/24.0 = 0.250 mol
So, 0.250 mol of CO2 is produced by 0.250 mol of MgCO3
Mr of MgCO3 = 84.3 x 0.250 = 21.1g
At what temperature will 1.28g of chlorine gas occupy 98.6 dm3, at a pressure of 175 Pa?
Moles of Cl2 = (1.28/(35.5 x 2)) = 0.0180 mol
Rearranging pV=nRT to find T gives T = (pV)/nR
So, T = (175 x (98.6 x 10-3))/(0.0180 x 8.314) = 115 K
Explain why the bond enthalpy of C=O in ketones is greater than the bond enthalpy of C-O in alcohols
The C=O bond consists of four shared electrons. The C-O bond is only made up of two shared electrons. This means there is a greater electron density between the positive nuclei in the C=O bond, so the nuclei are more strongly attracted to the shared electrons
Hydrogen peroxide has the structure: H-O-O-H
Using values from the table, calculate the overall enthalpy change for the reaction:
H2O2(aq) –> H2O(l) + ½O2(g)
Overall enthalpy change = total energy absorbed - total energy released
= [(2 x 463) + (1 x 146)] - [(2 x 463) + (½ x 498)]
= 1072 - 1175 = 103 kJ mol-1
If the standard enthalpy change of formation of Al2O3(s) is -1676 kJ mol-1 and the standard enthalpy change of formation of MgO(s) is -602 kJ mol-1, calculate the enthalpy change of the following reaction:
Al2O3(s) + 3Mg(s) –> 2Al(s) + 3MgO(s)
ΔrHϴ = sum of ΔfHϴ (products) - sum of ΔfHϴ (reactants)
= [0 + (3 x -602)] - [-1676 + 0]
= 130 kJ mol-1
Write a balanced equation, including state symbols, for the complete combustion of propane gas.
C3H8(g) + 5O2(g) –> 3CO2(g) + 4H2O(l)
Using the values of ΔfHϴ given in the table, draw an enthalpy cycle to determine the standard enthalpy of combustion of propane. Hence, calculate a value for ΔcHϴ [propane]
ΔcHϴ = sum of ΔfHϴ (products) - sum of ΔfHϴ (reactants)
= [(3 x -394.0) + (4 x -285.0)] - [(-104.7) + 0]
= -2221 kJ mol-1
The equation below shows the fermentation of glucose
C6H12O6(s) –> 2C2H5OH(l) + 2CO2(g)
Calculate the enthalpy change for the reaction.
Use the enthalpy cycle and the standard enthalpies of combustion shown below in your calculations
ΔrHϴ = ΔcHϴ (glucose) - 2ΔcHϴ (ethanol)
= [-2820] - [2 x -1367]
= -86 kJ mol-1
The initial temperature of 25.0 cm3 of 1.00 mol dm-3 hydrochloric acid in a polystyrene cup was measured at 19.0 oC. This acid was exactly neutralised by 25.0 cm3 of 1.00 mol dm-3 sodium hydroxide solution.
The maximum temperature of the resulting solution was measure as 25.8oC
Calculate the standard enthalpy change of neutralisation for the reaction. (You many assume the neutral solution formed has a specific heat capacity of 4.18 J g-1 K-1, and a density of 1.00g cm-3.)
Δ*T* = 25.8 - 19.0 = 6.80<sup>o</sup>C = 6.80 K m = 25.0 + 25.0 = 50.0 cm<sup>3</sup> of solution, which has a mass of 50.0g
Assume density to be 1.00g cm-3
Heat produced by reaction = mcΔT
= 50.0 x 4.18 x 6.80 = 1421.2 J
No. of moles of HCl = 1 x (25.0/1000) = 0.0250
No. of moles of NaOH = 1 x (25.0/1000) = 0.0250
Therefore, no. of moles of water = 0.0250
Producing 0.0250 mol of water takes 1421.2 J of heat, therefore producing 1 mol of water takes 1421.2/0.0250 = 56 848 J
= 58.6 kJ
So enthalpy change is -56.8 kJ mol-1 (3.s.f)
negative - because exothermic
A 50.0 cm3 sample of 0.200 mol dm-3 copper(II) sulfate solution placed in a polystyrene beaker gave a temperature increase of 2.00 K when excess zinc powder was added and stirred. (Ignore the increase in volume due to the zinc.)
Calculate the enthalpy change when 1 mol of zinc reacts. Assume the solution’s specific heat capacity is 4.18 J g-1 K-1. The equation for the reaction is: Zn(s) + CuSO4(aq) –> Cu(s) + ZnSO4(aq)
No. of moles of CuSO4 = 0.200 x (50.0/1000) = 0.0100 mol
From the equation, 1 mole of CuSO4 reacts with 1 mole of Zn
So, 0.0100 mol of CuSO4 reacts with 0.0100 mol of Zn
Heat produced by reaction = mcΔT
= 50.0 x 4.18 x 2.00 = 418 J
0.0100 mol of zinc produces 418 J of heat, therefore 1 mol of zinc produces 418/0.0100 = 41800 J = 41.8 kJ
So the enthalpy change is -41.8 kJ
A 50.0 cm3 sample of 0.200 mol dm-3 copper(II) sulfate solution placed in a polystyrene beaker gave a temperature increase of 2.00 K when excess zinc powder was added and stirred. (Ignore the increase in volume due to the zinc.)
The equation for the reaction is: Zn(s) + CuSO4(aq) –> Cu(s) + ZnSO4(aq)
Draw a labelled enthalpy profile diagram for this reaction, showing Ea and ΔrH
The following reaction represents an important stage in the industrial manufacture of sulfuric acid
2SO2(g) + O2(g) –> 2SO3(g)
The catalyst used is V2O5(s). Explain why this is considered a heterogeneous catalyst.
V2O5(s) is classed as a heterogeneous catalyst, as it is in a different state/phase from the reactants
Vanadium(V) oxide’s a solid, but the reactants are gases
The following reaction represents an important stage in the industrial manufacture of sulfuric acid
2SO2(g) + O2(g) –> 2SO3(g)
The catalyst used is V2O5(s). How could you show, experimentally, that V2O5(s) is a catalyst and not a reactant?
Find the mass of the V2O5(s) before and after the reaction - if it is acting as a catalyst, they will be the same
The following reaction represents an important stage in the industrial manufacture of sulfuric acid
2SO2(g) + O2(g) –> 2SO3(g)
The catalyst used is V2O5(s). Platinum catalysts are more efficient than vandium catalysts but are seldom used because they are susceptibel to poisoning by arsenic. Suggest an explanation for how the poisoning happens
The arsenic probably clings to the surface of the platinum and stops it getting involved in the reaction
This is how heterogeneous catalysts are normally poisoned
Crude oil is a source of fuels and petrochemicals. It’s vaporised and separated into fractions using fractional distillation. Some heavier fractions are processed using cracking
Give one economic reason why a catalyst is used in the cracking process
Cracking can be carried out at lower temperatures and pressures using a catalyst
Crude oil is a source of fuels and petrochemicals. It’s vaporised and separated into fractions using fractional distillation. Some heavier fractions are processed using cracking
Write an equation for the thermal cracking of dodecane, C12H26
E.g. C12H26 –> C2H4 + C10H22
Many answers - make sure C’s and H’s balance and there’s an alkane and an alkene
There are a number of different molecules with the molecular formula C5H10
Draw an unbranched cycloalkane with this fomula
There are a number of different molecules with the molecular formula C5H10
Draw a branched alkene with this fomula
There are a number of different molecules with the molecular formula C5H10
Draw an unbranched alkene with this fomula
Draw the structure of the molecule 3-methylbutan-2-ol
Draw the three-dimensional structure of propene. Mark two different bond angles on your diagram. Label each of these angles with its size.
Propene contains sigma bonds and one pi bond. Draw a labelled diagram showing where the pi bond is in the molecule and the electron arrangement in the bond.
Below is the structural formula of propa-1,2-diene. Mark two different bond angles on your diagram. Label each of these angles with its size.
Draw the structural formula for methanol
Draw the three-dimensional structure of methanol. On your diagram, mark one tetrahedral bond angle
Explain why the molecule exists in this shape
Electron pairs repel each other. This shape allows the electron pairs to be as far apart as possible
Draw the two structural isomers of chloropropane (C3H7Cl)
Draw the structural and skeletal formula of a cyclic alkane with the formula C6H12
Draw the structural and skeletal formula of a branched alkene with the formula C4H8
Name the molecule below
propan-1-ol
Name the molecule below
2-methylbutane
Which three of the following molecules are structural isomers?
A, B and C
A, B and C have the molecular formula C10H12O2
D has the molecular formula C11H14O2
Draw and name the E/Z isomers of pent-2-ene
Explain why alkenes can have E/Z isomers but alkanes cannot
E/Z isomers occur because atoms can’t rotate about C=C double bonds like they can around single bonds
Alkenes contain C=C double bonds and alkanes do not, so alkenes can form E/Z isomers and alkanes can’t
Which of the following molecules is an E isomer?
B
Name the molecule below
trans-2-chlorobut-2-ene
Name the molecule below
Z-hex-3-ene
Chloroethene CH2=CHCl forms the polymer poly(chloroethene), commonly known as PVC.
Write an equation to show the polymerisation of chloroethene. Your equation should show clearly the structure of the repeating unit in poly(chloroethene).
Write an equation using shortened structural formulas for the reaction of pent-2-ene with hydrogen gas
Give details of a chemical test that would enable you to distinguish between the product and the reactant. You should include details of how your results should be interpreted
CH3CH2CH=CHCH3 + H2 –> CH3CH2CH2CH2CH3
Add bromine water to samples of each substance and shake mixture. With pentane, the solution will remain orange. With pent-2-ene, the solution will become colourless
Ethene can undergo a hydrolysis reaction with cold water in the presence of a catalyst
Name the catalyst that can be used in the reaction
sulfuric acid
Ethene can undergo a hydrolysis reaction with cold water in the presence of a catalyst
Describe what happens in the two stages of this reaction
The ethene reacts with the sulfuric acid to form ethyl hydrogen sulfate. The ethyl hydrogen sulfate then reacts with water/is hydrolysed to form ethanol
Write a balanced equation for the complete combustion of hexane
C6H14 + 9½O2 –> 6CO2 + 7H2O
or 2C6H14 + 19O2 –> 12CO2 + 14H2O
Write a balanced equation for the incomplete combustion of pentanol
C5H11OH + 5O2 –> 5CO + 6H2O
Explain why burning an alkane in a limited supply of oxygen is potentially dangerous
if there is not enough oxygen to allow the fuel to burn fully, then incomplete combustion takes place. One of the products of incomplete combustion is carbon monoxide (CO), which is poisionous
Explain how the burning of fossil fuels in a car engine can lead to photochemical smog
Oxides of nitrogen (NOx) are produced when nitrogen and oxygen atoms in the air react together as a result of the high temperature and pressure in an engine. Unburnt hydrocarbons and these nitrogen oxides react with in the presence of sunlight to form ground-level ozone (O3), which is a major component of smog
State how the levels of the pollutants that lead to photochemical smog can be reduced
E.g. catalytic converters on cars can remove unburnt hydrocarbons and oxides of nitrogen from the exhaust
A problem caused by pollution is acid rain.
Name two pollutants which lead to acid rain, and explain how this problem can be reduced.
Sulfur dioxide and nitrogen dioxide escape into the atmosphere. The problem can be reduced by using calcium oxide to remove sulfur dioxide from power station flue gases
Catalytic converters can remove both from vehicle emissions
Describe two types of measure that governments can take to try to reduce pollution
change the law/tax pollution more highly/encourage people to change their behaviour/fund the development of new fuels that cause less pollution
Describe two advantages associated with the continued large-scale use of fossil fuels as an energy source
Continued use of fossil fuels means increasing amounts of carbon dioxide being emitted, which could lead to problems with climate change.
Fossil fuels are also non-renewable, and so they will eventually run out, leading to problems if we do not have alternatives
Give two reasons why the demand for energy is rising
E.g. The world’s population is rising so there are more people demanding energy
Developing countries are getting richer, meaning their industry is growing and more energy-consuming products are being bought
Describe one advantage and one disadvantage of using wind power as a fossil fuel alternative
Advantage - wind power does not emit carbon dioxide into the atmosphere (although CO2 will be emitted during the manufacture of wind turbines)
Disadvantage - wind power is not completely reliable
Describe one advantage and one disadvantage of using hydrogen as a fossil fuel alternative
Advantage - hydrogen is a ‘clean’ fuel whose only waste product is water
Disadvantage - it takes energy to extract from seawater
In a classroom debate on the future of fuels, Martin argues that bioethanol is not a solution to the Earth’s ‘greenhouse effect’ problem because “the combustion of bioethanol still produces carbon dioxide”
However, Samantha maintains that bioethanol is “carbon neutral”
To what extent are Martin and Samantha’s arguments right or wrong?
Burning biofuels does produce carbon dioxide, although it is CO2 that the plants, that go into making biofuels, absorbed while they were growing. This is why biofuels are often considered to be carbon neutral. However CO2 is also given out while refining and transporting the fuel so the overall production is not carbon neutral
In a classroom debate on the future of fuels, Martin argues that bioethanol is not a solution to the Earth’s ‘greenhouse effect’ problem because “the combustion of bioethanol still produces carbon dioxide”
However, Samantha maintains that bioethanol is “carbon neutral”
Describe two disadvantages of replacing fossil fuels with biofuel
E.g. Petrol engines in cars would have to be modified to use biofuels. Land currently used for farming might be used to grow the crops used to produce biofuel, which might cause food shortages in developing countries
