Chemistry mixed exam questions Flashcards
Give one reason why the value calculated from mean bond enthalpies is different from the value given in the databook
it is not specific for this reaction
or
they are average values from many different compounds/molecules
what is the equation to work out mean bond enthalpies?
btw this is worth a mark, so write it down in case you get the whole question wrong
June 2010
(Sum of ) bonds broken – (Sum of) bonds made/formed = ΔH
or
(⅀) B reactants – (⅀) B products = ΔH
It has been claimed that there is no net carbon (greenhouse gas) emission to the
the atmosphere when ethanol made by Process 2 is used as a fuel.
State the term that is used to describe fuels of this type.
Use the equations for Processes 1, 2 and 3 to show why it can be claimed that there is
no net emission of carbon-containing greenhouse gases.
3 marks
June 2010
The term is carbon neutral
6 moles of carbon dioxide are taken in by photosynthesis
4 moles are released in process 2 and 2 moles are released in process 3
Two different chlorine-containing compounds are formed when chlorine reacts with
cold, dilute sodium hydroxide solution. One of these compounds is sodium chloride.
Name the other chlorine-containing compound formed. (1 mark)
June 2010
Sodium chlorate(I)
Name one possible compound which could be S. (1 mark)
by the way, r in the question had a c=c bond but they both had the molecular formula of c6h12
June 2010
cyclohexane
Sulfuric acid behaves as an oxidising agent in Reaction
In terms of electrons state the meaning of the term oxidising agent. ( 1 mark)
June 2010
an electron acceptor or it gains electrons
The formation of ethanol in Reaction 3 uses concentrated sulfuric acid and proceeds in
two stages according to the following equations.
Stage 1 H2C=CH2 + H2SO4 CH3CH2OSO2OH
Stage 2 CH3CH2OSO2OH + H2O CH3CH2OH + H2SO4
State the role of sulphuric acid in these reactions (1 mark)
June 2010
It is an acid catalyst
State the meaning of the term molecular ion (1 mark)
June 2010
A molecule with an electron knocked off or a 1+ ion
State why the precise relative atomic mass for the 12C isotope is exactly 12.00000
By definition
Use your knowledge of the reactions of halide ions with silver nitrate to suggest why
the student did not include 1-fluorobutane in this experiment.
AgF is soluble in water so the student would see no visible change
Write an overall equation for the redox reaction of chlorate(I) ions with hydrochloric acid.
ClO− + Cl− + 2H+ → Cl2 + H2O
Write a half-equation for the reduction of chlorate(l) ions to chlorine in acidic conditions.
2ClO− + 4H+ 2e-→ Cl2 + 2H2O
Write a half-equation for the oxidation of chloride ions
2Cl → Cl2 + 2e(-)
A solution of sodium chlorate(l) was added to a colourless solution of potassium iodide.
Suggest what is observed.
Explain the reaction that leads to this observation
Goes brown (or shades of brown)
Due to iodine or I3−
Because I− oxidised
