GCSE – Chemistry – Grade 9 Question with Mark scheme & Detailed Explanation

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Question:

Explanation:

What is Cracking ?

• Converting long hydrocarbon chain molecule into small hydrocarbon chain molecule
• It’s is a Thermal decomposition reaction , that helps to breaking a molecule by heating
• Heating the long chain molecule and vaporise them is very common in cracking

Types of cracking:

• Catalytic cracking (Eg. Making ethanol from Sugarcane)
• Steam cracking (Eg. Making ethanol from Crude oil)

Detailed explnation:

The products of cracking include alkanes and alkenes. In the question they have supplied the name of one of the product is Ethene ( C₂H₄ ). So the second product will be an alkane which contain rest of the C and H atoms . Hence the balance carbon will be ( 6 – 2 = 4) and the balance hydrogen will be ( 14 – 4 = 10). So the name of the other compound will be Butane (C₄H₁₀ ).

Mark Scheme:

Question:

Mark scheme

Question:

Detailed Explanation:

Ethanol from Sugar	Ethanol from Crude Oil
Carbon neutral (Reduce global warming) (Sugar cane plants absorb CO2 during photosynthesis)	High cost
Sugar cane plants are renewable. Hence save resources	Crude Oil is Non-renewable
Low energy processing	High energy processing (Need energy for fractional distillation and cracking )
Large areas of land need to cultivate sugar cane. This leads destruction of the habitats & forest.
Ethanol is impure (contains 50% ethanol)	100% pure
Supply of ethanol is seasonal
Batch process (Very slow process)	Continuous process

Mark Scheme: