As Chem Paper 2 Flashcards
Hexane is a saturated hydrocarbon.
State what is meant by the term ‘saturated hydrocarbon’. Your answer should refer to both words in the term (2)
saturated means all bonds (between C atoms) are single (1)
• hydrocarbon contains hydrogen and carbon only
When methane reacts with gaseous chlorine, the initiation step is bond breaking in the chlorine molecule to form chlorine free radicals.
The equation for this step is shown.
Cl2(g) → 2Cl•(g)
Two equations for the propagation step are shown.
Cl•(g) + CH4(g) → CH3•(g) + HCl(g)
CH3•(g) + Cl2(g) → CH3Cl(g) + Cl•(g)
(i) Write the overall equation for this reaction of methane with chlorine.
State symbols are not required.
CH4 +Cl2 -> CH3Cl +HCl
When methane reacts with gaseous chlorine, the initiation step is bond breaking in the chlorine molecule to form chlorine free radicals.
The equation for this step is shown.
Cl2(g) → 2Cl•(g)
Two equations for the propagation step are shown.
Cl•(g) + CH4(g) → CH3•(g) + HCl(g)
CH3•(g) + Cl2(g) → CH3Cl(g) + Cl•(g)
(ii) Calculate the maximum mass, in grams, of chloromethane produced when 7.00 g of chlorine gas reacts completely with excess methane. (2)
[Molar mass of CH3Cl = 50.5 g mol–1]
moles of chlorine molecules = 7.00 ÷ 71 = 0.098592 (mol)
Do not award use of 70 for the molar mass of chlorine molecule
1 mole chlorine molecules produces 1 mole CH3Cl moles of CH3Cl = 0.098592 (mol)
= 0.098592 × 50.5 = 4.9789 (g) = 4.98 / 5.0 / 5 g
TE on mol of chlorine
Ignore SF including 1 SF
Allow TE from equation in (b)(i)
Use 35.5 for the molar mass to give 9.96 g scores M2
When methane reacts with gaseous chlorine, the initiation step is bond breaking in the chlorine molecule to form chlorine free radicals.
The equation for this step is shown.
Cl2(g) → 2Cl•(g)
Two equations for the propagation step are shown.
Cl•(g) + CH4(g) → CH3•(g) + HCl(g)
CH3•(g) + Cl2(g) → CH3Cl(g) + Cl•(g)
(iii) Write an equation for a termination step for this reaction. State symbols are not required. (1)
CH3• + CH3.~> C2H6
Or
Cl• + Cl•-> Cl2
Or
CH3• + Cl•-> CH3Cl
Or
2CH3•-> CH3CH
Further substitution of chloromethane can occur, producing dichloromethane, which is a liquid at room temperature.
Calculate the maximum volume, in cm3, of dichloromethane liquid that could be produced from 12.5 g of chloromethane.
Give your answer to an appropriate number of significant figures.
(3)
CH3Cl(g) + Cl2(g) → CH2Cl2(l) +HCl(g)
[Density of dichloromethane, CH2Cl2(l) = 1.32 g cm–3]
12.5 ÷ 50.5 = 0.24752
Mr CH2Cl2 = 85
0.24752 × 85 = 21.040 (g)
21.040 ÷ 1.32 = 15.939 (cm3) = 15.9 / 16 (cm3)
calculation of mol CH3Cl (1)
• calculation of mass of CH2Cl2 produced (1)
• conversion of mass to volume of liquid using density and
answer given to 2 or 3 SF only (1)
Commercial diesel fuel is a mixture of hydrocarbons.
One of the components of commercial diesel fuel is a hydrocarbon with the formula C12H26 .
An equation for the complete combustion of C12H26 is shown. C12H26(l) + 181⁄2O2(g) → 12CO2(g) + 13H2O(l)
(i) Calculate the maximum volume, in m3, of carbon dioxide gas produced in an engine by the complete combustion of 1.00 kg of C12H26 at 200 °C, at a pressure of 6.0 × 106 Pa.
(4 marks)
[The ideal gas equation is pV = nRT Gas constant, R = 8.31 J mol–1 K–1]
1.00 kg = 1000 g
C12H26 = 170 g mol−1
moles C12H26 = 1000 ÷ 170 = 5.8824 (mol)
moles of CO2 = 5.8824 × 12 = 70.588 (mol)
T = 200 + 273 = 473 K
and
V = nRT/p
V = 70.588 x 8.31 x 473 6 x 106
V = 0.046243 (m3)
Biodiesel is derived from plants and petrodiesel is derived from crude oil. Biodiesel is increasingly widely used, although it is more expensive and provides less energy per kg when burned than petrodiesel.
Give one reason why biodiesel is now preferred to petrodiesel. (1)
Renewable / sustainable resource (derived from plant matter)
Cleaner burning (because it contains oxygen in the molecule)
Better lubricant (than petrodiesel)
Uses up waste (cooking) oils
Plants grown locally so less dependent on import
This question is about alkenes and some of their reactions. (a) Alkenes have the same general formula as cycloalkanes.
Explain why this general formula is different from that of alkanes. Include the general formulae in your answer (3 marks)
General formula of alkenes and/or cycloalkanes = CnH2n
General formula of alkanes = CnH2n+2. (Mark 1)
alkenes have a double bond (with two less hydrogens). (M2)
• cycloalkanes have carbons in a ring (resulting in two less hydrogens) (M3)
The industrial manufacture of margarine involves the addition of hydrogen to an alkene.
Which catalyst is used for this process?
A iron
B nickel
C phosphoric acid
D sodium hydroxide
B
What is the type and mechanism for the reaction of hydrogen bromide with propene?
A electrophilic addition
B electrophilic substitution
C nucleophilic addition
D nucleophilic substitution
A
Various methods are used to reduce the problem of plastic waste, including the incineration, recycling and introduction of biodegradable polymers.
(i) Describe how the toxic gas hydrogen chloride produced during the incineration of poly(chloroethene) could be removed.(1)
• scrubbing with alkali / pass through any alkaline solution eg NaOH(aq) /over solid base e.g. CaO
(ii) Give a reason why some polymers cannot be recycled.
(1)
…………………………………………………………………………………………………………………………………………………………………………
Polymer degrades during heating (for recycling)
Heavy pigmentation/ colour of plastic to be recycled
Thermoset / 3D polymers cannot be recycled (because of their structure)
It’s difficult to separate polymers into types
