Hydrogen Peroxide

7) Aqueous hydrogen peroxide is used to sterilise contact lenses. At room temperature, aqueous hydrogen peroxide decomposes very slowly to form water and oxygen.

The decomposition can be represented by the equation below:

2  H – O – O – H     O = O   +  2 H – O – H       ∆H = – 206 kJ/mol

 

a) With reference to the energy changes during bond breaking and bond formation, describe and explain how the temperature of the solution changes when aqueous hydrogen peroxide decomposes.
a) With reference to the energy changes during bond breaking and bond formation, describe and explain how the temperature of the solution changes when aqueous hydrogen peroxide decomposes.
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b)

The table shows some bond energies, measured in kilojoules per mole, kJ/mol.

Bond	Bond energy in kJ/mol
O – H	463
O = O	496

Use the data provided to calculate the bond energy for the O – O bond in hydrogen peroxide.

 

8)      An organic compound X has a structural formula as shown in the diagram below:

1. a) Isomers can have different functional groups.

(i)   Write the molecular formula of compound X.                                ………………

(ii)   An isomer of compound X has the condensed formula CH₂CHCOOCH₃.                       Draw the full structural formula of CH₂CHCOOCH₃.

 

1. b) The following tests were carried out on compound X.

Test I       Compound X is shaken with aqueous bromine to give compound A.Test II     Magnesium ribbon is added to an aqueous solution of compound X. Test III     On refluxing with a little concentrated sulfuric acid, compound X reacts with methanol to give another compound B.

 

(i)   Describe an observation made in Test I and explain your answer.

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(ii)  Draw the full structural formula of compound A.

(iii) Construct a balanced chemical equation for the reaction in Test II.

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(iv)  State one physical property of compound B.                                                     ……………………………………………………………………………………………

 

 

 

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Did you answer the Secondary Chemistry Tuition Question correctly?

 

7.a. The temperature of the solution increased.

The energy released into the surrounding during bond making is greater than the energy absorbed during bond breaking.

1. Energy absorbed to break 4 O – H bonds and 2 O – O bonds

= 4(+463) + 2x

Energy released to form 1 O = O bond and 4 O – H bonds

= -496 + 4(-463)

4(+463) + 2x + (-496) + 4(-463) = -206

                                                x = 145

O – O bond energy = 145 kJ/mol

8.a.i. C₄H₆O₂

b.i. Reddish-brown solution of bromine decolourises/ turns colourless.

Compound X is an unsaturated compound / contains C=C bond which allows bromine atoms to be added

 

1. Mg + 2 CH₃COOH → Mg(CH₃COO)₂ + H₂Learn from our Chemistry Tuition Question and Answer. Miracle Learning Centre Call 6463 8756 or sms 8128 8342/9839 9908.(Specialist in Science and Maths) for Primary, Secondary and JC levels.Miracle Learning Centre specialises in Physics tuition, Chemistry tuition, Maths tuition and Science tuition Classes.