1 Bromine is a reactive element. It combines with other non-metals to form covalent compounds. Phosphorus tribromide, PBr3, and iodine monobromide, IBr, are examples of covalent compounds used in organic synthesis.
(a) PBr3 can be prepared by heating bromine with phosphorus, P4.
(i) Write an ...
1 bromine is a reactive element it combines with other non metals to form covalent compounds phosphorus tribromide
are examples of covalent compounds used in orga
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Chemistry
PMT
AS Level Chemistry A
H032/02 Depth in chemistry
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1 Bromine is a reactive element. It combines with other non-metals to form covalent compounds.
Phosphorus tribromide, PBr3, and iodine monobromide, IBr, are examples of covalent compounds used in
organic synthesis.
(a) PBr3 can be prepared by heating bromine with phosphorus, P4.
(i) Write an equation for this reaction.
…………………………………………………………………………………………. [1]
(ii) How many molecules are present in 1.3535 g of PBr3?
number of molecules =.......................................... [3]
(iii) The ‘dot-and-cross’ diagram of a molecule of PBr3 is given below.
Name the shape of this molecule and explain why the molecule has this shape.
name: ………………………………………………………………………………………..
explanation: ………………………………………………………………………………….
……………………………………………………………………………………………….
……………………………………………………………………………………………….
[3]
Chemistry H032/02
, PMT
3
(b) Bromine reacts with iodine to form iodine monobromide, IBr.
The table below lists some average bond enthalpies which are required in different parts of this
question.
Bond Average bond enthalpy / kJ mol1
Br–Br +193
I–I +151
I–Br +175
(i) Average bond enthalpy is the enthalpy change for the breaking of 1 mole of bonds in
gaseous molecules.
Why do Br2 and I2 not exist in the gaseous state under standard conditions?
……………………………………………………………………………………………….
……………………………………………………………………………………….. [1]
(ii) Calculate the enthalpy change of formation, fH, for IBr.
fH = ……………………… kJ mol1 [2]
(c) Iodine monobromide, I–Br, is a polar molecule.
Heterolytic fission of the I–Br bond forms an electrophile.
State the meaning of the term electrophile and suggest the formula of the electrophile formed from
IBr.
……………………………………………………………………………………………….
……………………………………………………………………………………….. [2]
(d) Bromine disproportionates when it reacts with potassium hydroxide solution.
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