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Chem unit 1 pastpap2

QuestionAnswer
This question is about hexane, C6H14, and hex-1-ene, C6H12. What test would you use to distinguish between hexane and hex-1-ene Give the results of the test for each substance, Test : add bromine (water) /bromine solution bromine gas /bromination (1) Result: no change with hexane / stays orange brown/ stays red brown/ stays yellow and goes colourless with hex-1-ene(1) OR
Give the results of the test for each substance, Test : add (acidified) potassium manganate((VII)(solution)ALLOW potassium permanganate Result: no change with hexane/stays purple And goes colourless / brown with hex-1-ene (1) OR
Give the results of the test for each substance, Test : add alkaline potassium manganate((VII))(solution)(1) ALLOW potassium permanganate Result: no change with hexane/stays purple and goes green with hex-1-ene (1)
Explain why stereoisomerism can occur in alkenes, and why hex-2-ene has stereoisomers but hex-1-ene does not C=C restricts rotation/ C=C prevents twisting /C=C can’t rotate/ lack of free rotation round C=C (so the groups can’t change position relative to the bond)
Hex-1-ene has no group which takes priority on the C at one end of C=C &.. Hex–2-ene has different groups on the C at each
The value for the enthalpy change of combustion in this experiment is different from the value given in data books. Suggest TWO reasons for this difference Heat losses (from calorimeter)/ poor insulation • Incomplete combustion/burning • Evaporation of fuel (after weighing) heat absorbed by calorimeter. Heat capacity of calorimeter. Measurements not carried out under standard conditions.
A student suggested that the results would be more accurate if a thermometer which read to 0.1°C was used. Explain why this would not improve the accuracy of the result. A calculation is not required. Error in reading temperature is less than the effect of ignoring heat loss.
C6H12(l) + H2(g) → C6H14(l) (i) What catalyst is used in this reaction? nickel.
Explain why the values(standard enthalpy change) are so similar same(number and type of) bonds are broken. and made in each reaction / one C=C (and one H-H) are broken and two C-H made
Chloroethae, C2H5Cl, can be made from either ethane or ethene.(i) What reagent and condition would be used to make chloroethane from ethane Reagent: chlorine/ Cl2 (1) Condition: uv/ sunlight
State the type of reaction and mechanism by which this reaction occurs (free) radical (1) Substitution
What reagent would be used to make chloroethane from ethene Hydrogen chloride / HCl
Which of making chloroethane has electrophilic addition a higher atom economy Higher atom economy from ethene /by Higher yield from ethane
From ethene one product / all atoms are used making product /no unwanted products
For ethene yield high as no di-, tri- etc substituted products form /only one product / no by-products OR no side reactions occur OR no C4 compounds can form.
PVC. Almost a quarter of the PVC used to make water pipes,formerly made of metal. Give TWO factors considered when deciding PVC or metal, contributes to more sustainable uses of resources. Energy for man materials/lifetime of product/how often need replaced /metal rusts/plastic more easily punctured etc • ease of recycling/steel an excellent recyclable material/consequences of disposal/is it biodegradable? from a non-renewable resource?
The compound butane has the empirical formula C2H5 and the molecular formula C4H10.
Avogadro constant 6.0 × 1023 mol–1. Therefore the number of atoms in 1 mol of carbon dioxide is 1.8 × 1024
The enthalpy change for the reaction CH4(g) ---> C(g) + 4H(g) is +1648 kJ mol–1. Hence the mean bond enthalpy for the C–H bond is / by 4 +412kjmol-1
Ethane reacts with chlorine when the substances are exposed to UV radiation. The equation for this reaction C2H6 + Cl2 --> C2H5Cl + HCl.
The role of the UV radiation in the reaction is to break the Cl Cl bond forming Cl• free radicals
Created by: ufuoma
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