AQA chemistry unit 2

Everything from papers to revision to questions!!! on AQA unit 2 Chemistry.....June 2010

I found these qns on Haloalkanes on a site. They seem really useful

1. Methylbenzene is converted into (chloromethyl)benzene in a free radical substitution reaction.
C6H5CH3 + Cl2  C6H5CH2Cl + HCl
(i) Write an equation for the initiation step.
...........................................................................................................................
(1)
(ii) Write equations for the two propagation steps.

(2)
(iii) Give the formula of another possible organic product of the reaction.
...........................................................................................................................
(1)
(Total 4 marks)
2. The reaction of bromine with ethane is similar to that of chlorine with ethane. Three steps in the bromination of ethane are shown below.
Step 1 Br2 2Br•
Step 2 Br• + CH3CH3 CH3CH2•˙ + HBr
Step 3 CH3CH2• + Br2 CH3CH2Br + Br•
(a) (i) Name this type of mechanism.
...........................................................................................................................
(ii) Suggest an essential condition for this reaction.
...........................................................................................................................
(iii) Steps 2 and 3 are of the same type. Name this type of step.
...........................................................................................................................
(iv) In this mechanism, another type of step occurs in which free-radicals combine. Name this type of step. Write an equation to illustrate this step.
Type of step .......................................................................................................
Equation.............................................................................................................
(5)
(b) Further substitution in the reaction of bromine with ethane produces a mixture of liquid organic compounds.
(i) Name a technique which could be used to separate the different compounds in this mixture.
...........................................................................................................................
(ii) Write an equation for the reaction between bromine and ethane which produces hexabromoethane, C2Br6, by this substitution reaction.
...........................................................................................................................
(2)
(Total 7 marks)
3. (a) Dichloromethane, CH2Cl2, is one of the products formed when chloromethane, CH3Cll, reacts with chlorine.
(i) Name the type of mechanism involved in this reaction and write an equation for each of the steps named below.
Name of type of mechanism ...............................................................................
Initiation step
............................................................................................................................
First propagation step
............................................................................................................................
Second propagation step
............................................................................................................................
(ii) Write an overall equation for the formation of dichloromethane from chloromethane.
...........................................................................................................................
(5)
(b) A compound contains 10.1% carbon and 89.9% chlorine by mass. Calculate the molecular formula of this compound, given that its relative molecular mass (Mr) is 237.0
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(3)

(c) Suggest the formulae of two bromine-containing organic compounds formed when dibromomethane, CH2Br2, reacts with bromine.
Compound 1 ...............................................................................................................
Compound 2 ...............................................................................................................
(2)
(Total 10 marks)

4. (a) When 3-bromo-2,3-dimethylpentane, (CH3)2CHCBr(CH3)CH2CH3, reacts with aqueous potassium hydroxide, an alcohol is formed.
(i) Name the type of reaction taking place and give the role of the reagent.
Type of reaction ...............................................................................................
Role of reagent .................................................................................................

(ii) Outline a mechanism for the reaction, showing clearly the structure of the alcohol formed.

(5)

(b) When 3-bromo-2,3-dimethylpentane reacts with ethanolic potassium hydroxide, three structurally isomeric alkenes are formed.
(i) Name the type of reaction taking place and give the role of the reagent.
Type of reaction ...............................................................................................
Role of reagent .................................................................................................
(ii) One of the reaction products is 2,3-dimethylpent-2-ene.
Give the structure of this alkene and outline a mechanism for its formation.
Structure of alkene

Mechanism

(iii) Give the structures and names of the other two alkenes which are also formed.
Structure of second alkene

Name .................................................................................................................

Structure of third alkene

Name .................................................................................................................
(10)
(Total 15 marks)
5. Bromoethane, CH3CH2Br, reacts with sodium hydroxide in an elimination reaction to form ethene.
(i) Outline a mechanism for this elimination reaction.

(ii) Suggest one reason why this method for making ethene is not used in industry.
...........................................................................................................................
...........................................................................................................................
(4)
(Total 4 marks)
6. Consider the following scheme of reactions.

In Reactions 2 and 5, bromoethane undergoes nucleophilic substitution.
(i) Identify a reagent for Reaction 2. Name the organic product, P.
Reagent for Reaction 2 .....................................................................................
Name of product P .........................................................................................
(ii) Identify a reagent for Reaction 5. Name the organic product, Q.
Reagent for Reaction 5 ..................................................................................
Name of product Q .........................................................................................

(iii) Outline a mechanism for Reaction 5.

(8)
(Total 8 marks)

7. (a) Draw the structure of 2-bromo-3-methylbutane.

(1)
(b) (i) Draw the structure of methylbut-2-ene.

(ii) Methylbut-2-ene is formed when 2-bromo-3-methylbutane is treated with ethanolic potassium hydroxide. Name and outline the mechanism for this reaction.
Name of mechanism .........................................................................................
Mechanism

(5)
(c) Name the isomer of methylbut-2-ene which is also formed when 2-bromo-3-methylbutane is treated with ethanolic potassium hydroxide.
.....................................................................................................................................
(1)
(Total 7 marks)

8. When 2-chloropropane reacts with sodium hydroxide, two different reactions occur.
Each reaction produces a different organic product.

(i) Outline a mechanism for Reaction 1 and state the role of the hydroxide ion in this reaction.
Mechanism

Role of the hydroxide ion .................................................................................
(ii) Outline a mechanism for Reaction 2 and state the role of the hydroxide ion in this reaction.
Mechanism

Role of the hydroxide ion .................................................................................
(7)
(Total 7 marks)

9. (a) A substitution reaction occurs when 2-bromopropane reacts with aqueous sodium hydroxide.
(i) Draw the structure of the organic product of this reaction and give its name.
Structure

Name ...........................................................................................................
(ii) Name and outline the mechanism for this reaction.
Name of mechanism ......................................................................................
Mechanism

(5)
(b) Under different conditions, 2-bromopropane reacts with sodium hydroxide to produce propene.
(i) Name the mechanism for this reaction.
......................................................................................................................

(ii) State the role of sodium hydroxide in this reaction.
......................................................................................................................
(2)
(Total 7 marks)

10. Consider the following reaction scheme.

(a) Give a suitable reagent and state the essential conditions required for Reaction 3.
Reagent ...………………………………….…………………………………….…..
Conditions ..…………………..……………………………………………………..
(2)
(b) The reagent used for Reaction 3 can also be used to convert 2-bromopropane into propene. State the different conditions needed for this reaction.
.....................………………………………………………………………………….
(1)
(Total 3 marks)
11. Compound X, (CH3)2CHCN, can be formed from a haloalkane, C3H7Br.
(i) Name compound X.
...........................................................................................................................
(ii) Give the reagent and conditions necessary to form X from C3H7Br.
Reagent..............................................................................................................
Conditions..........................................................................................................
(iii) Name and outline the mechanism for this reaction, showing clearly the structure of C3H7Br.
Name of mechanism..........................................................................................
Mechanism

(7)
(Total 7 marks)

12. (a) The equation below shows the reaction of 2-bromopropane with an excess of ammonia.
CH3CHBrCH3 + 2NH3  CH3CH(NH2)CH3 + NH4Br
Name and outline the mechanism involved.
Name of mechanism ...............................................................................................
Mechanism

(5)

(b) When 2-bromopropane is heated with ethanolic potassium hydroxide, an elimination reaction occurs. State the role of potassium hydroxide and outline a mechanism for this reaction.
Role of potassium hydroxide ...................................................................................
Mechanism

(5)
(Total 10 marks)

13. Classify the following reaction.
C3H7Br + KOH  C3H6 + KBr + H2O
...............................................................................................................................
(1)
(Total 1 mark)
14. (i) Give the structural formula and name of the organic product of the reaction between CH3CH2CH2CH2Br and potassium cyanide.
Structural formula.............................................................................................
Name.................................................................................................................
(ii) Name and outline the mechanism involved in this reaction.
Name.................................................................................................................
Mechanism

(iii) Suggest why CH3CH2CH2CH2F reacts less rapidly than CH3CH2CH2CH2Br with potassium cyanide.
...........................................................................................................................
...........................................................................................................................
(6)
(Total 6 marks)

15. (a) Name and outline a mechanism for the reaction of 2-bromo-2-methylpropane with ethanolic potassium hydroxide to form the alkene 2-methylpropene, (CH3)2C=CH2
Name of mechanism ..................................................................................................
Mechanism

(4)

(b) When 2-bromo-2-methylpropane reacts with aqueous potassium hydroxide,
2-methylpropan-2-ol is formed as shown by the following equation.

State the role of the hydroxide ions in this reaction.
.....................................................................................................................................
(1)

(c) Write an equation for the reaction that occurs when CH3CH2CH2CH2Br reacts with an excess of ammonia. Name the organic product of this reaction.
Equation ......................................................................................................................
Name of product ..........................................................................................................
(3)
(Total 8 marks)
16. Alkenes can be made in the laboratory from halogenoalkanes by heating them with a suitable reagent. By a similar method, cyclohexene can be prepared from bromocyclohexane.
(i) Suggest the name of a suitable reagent and state an essential condition, other than heat, for this reaction, starting from bromocyclohexane.
Reagent .............................................................................................................
Condition ..........................................................................................................
(2)

(ii) Using graphical formulae, write an equation for this reaction.

(2)
(iii) Give the name of this type of reaction.
...........................................................................................................................
(1)
(Total 5 marks)

17. (a) (i) Write an equation for the reaction between 1-bromopropane and potassium cyanide.
...........................................................................................................................
(1)
(ii) Give the name of the type of mechanism involved in the reaction in (b)(i).
...........................................................................................................................
(1)
(b) Give the formula of the attacking species in (b) and state what feature of its structure is responsible for its role.
Formula ..........................................................................................................
Structural feature ............................................................................................
(2)
(Total 4 marks)

18. Consider the following reaction in which an alkene is formed from a haloalkane.

(a) Name the haloalkane used in this reaction.
.....................................................................................................................................
(1)
(b) Name and outline a mechanism for this reaction.
Name of mechanism ....................................................................................................
Mechanism

(4)
(Total 5 marks)

19. (a) The reaction of chloromethane with chlorine to form trichloromethane is a free radical substitution involving several propagation steps.
(i) Write an overall equation for this reaction.
............................................................................................................................
(ii) What is meant by the term propagation step?
............................................................................................................................
............................................................................................................................
(iii) Write an equation for a propagation step in which chloromethane reacts.
............................................................................................................................
(iv) Write an equation for a propagation step in which trichloromethane is formed.
............................................................................................................................
(4)
(b) Write an equation and outline a mechanism for the reaction of chloromethane with an excess of ammonia.
Equation .....................................................................................................................
Mechanism

(5)
(Total 9 marks)

20. When a mixture of chlorine with an excess of methane is irradiated with ultraviolet light, a reaction occurs with chloromethane as the main organic product.
Write an equation and a mechanism for the formation of chloromethane.
(5)
(Total 5marks)
21. Ethene can be converted into a variety of useful products as illustrated below.

(b) Give a reagent for reaction 5.
(1)
(Total 1 mark)

22. Consider the following scheme of reactions for making ethane-1,2-diol from ethene by two different routes.

Name and outline a mechanism for Reaction 3. Explain why compound Y is susceptible to attack by hydroxide ions.
(4)
(Total 4 marks)
23. Ethene is an important starting point for the manufacture of plastics and pharmaceutical chemicals. Most of the ethene used by industry is produced by the thermal cracking of ethane obtained from North Sea gas (Reaction 1). It is also possible to make ethene either from chloroethane (Reaction 2) or from ethanol (Reaction 3).

(a) Give essential conditions and reagents for Reaction 2.
(2)
(b) Name and outline a mechanism for Reaction 2. Suggest a reason why chloroethane is not chosen by industry as a starting material to make ethene commercially.
(5)
(Total 7 marks)

24. Reaction of 2-bromobutane with potassium hydroxide can produce two types of product depending on the solvent used. In aqueous solution, the formation of an alcohol, E, is more likely but in ethanolic solution the formation of alkenes is more likely.
(a) For each type of product, name the type of reaction occurring and state the role of the potassium hydroxide.
(4)
(b) Name alcohol E and draw its structural formula. By reference to the structure of the halogenoalkane, explain why the initial step in the mechanism of the reaction producing the alcohol occurs.
(5)
(Total 9 marks)

25. The structural formulae of compounds A, B, C and D, which are the four structural isomers of molecular formula C4H9Cl, are given below.
CH3CH2CH2CH2Cl CH3CH(Cl)CH2CH3 (CH3)2CHCH2Cl (CH3)2C(Cl)CH3
A B C D
(i) Give the name of compound D.
(1)
(ii) When refluxed with an alcoholic solution of KOH, compound B undergoes an elimination reaction. Two structurally isomeric products are formed. Draw the graphical formulae of these two structural isomers.
(2)
(iii) Draw the graphical formula for the product of the reaction between compound C and NaOH(aq). Give an outline of the mechanism involved in this reaction.
(4)
(Total 7 marks)

26. In aqueous ethanolic alkali, 2-bromo-2-methylbutane undergoes either substitution or elimination reactions to produce an alcohol or a mixture of two alkenes, respectively. Give the structures and names of these three compounds. Account for the formation of the various products by reference to the mechanisms of the reactions involved.
(14)
(Total 14 marks)

Reply 2

chanella

Questions on halogens, gr2 metals and redox
1. (a) By referring to electrons, explain the meaning of the term oxidising agent.
.....................................................................................................................................
(1)
(b) For the element X in the ionic compound MX, explain the meaning of the term oxidation state.
.....................................................................................................................................
(1)

(c) Complete the table below by deducing the oxidation state of each of the stated elements in the given ion or compound.
Oxidation state
Carbon in CO
Phosphorus in PCl
Nitrogen in Mg3N2
(3)

(d) In acidified aqueous solution, nitrate ions, NO , react with copper metal forming nitrogen monoxide, NO, and copper(II) ions.
(i) Write a half-equation for the oxidation of copper to copper(II) ions.
........................................................................................…...............................
(ii) Write a half-equation for the reduction, in an acidified solution, of nitrate ions to nitrogen monoxide.
........................................................................................…...............................
(iii) Write an overall equation for this reaction.
........................................................................................…...............................
(3)
(Total 8 marks)

5. (a) The following is an equation for a redox reaction.
2NO + 12H+ + 10I–  2NH4+ + 2H2O + 5I2

(i) Define oxidation in terms of electrons.
.....................................................................................................................

(ii) Deduce the oxidation state of nitrogen in NO and of nitrogen in NH4+
Oxidation state of nitrogen in NO .................................................................
Oxidation state of nitrogen in NH4+ ..............................................................

(iii) Identify the species formed by oxidation in this reaction...................................
(4)

(b) When chlorine gas is bubbled into an aqueous solution of sulphur dioxide, hydrogen ions, sulphate ions and chloride ions are formed.
(i) Write a half-equation for the formation of chloride ions from chlorine.
....................................................................................................................

(ii) Write a half-equation for the formation of hydrogen ions and sulphate ions from sulphur dioxide and water.
....................................................................................................................

(iii) Hence, deduce an overall equation for the reaction which occurs when chlorine is bubbled into aqueous sulphur dioxide.
....................................................................................................................
(3)
(Total 7 marks)

6. (a) In terms of electrons, what happens to an oxidising agent during a redox reaction?
.....................................................................................................................................
(1)

(b) Consider the following redox reaction.
SO2(aq) + 2H2O(l) + 2Ag+(aq) 2Ag(s) +(aq) + 4H+(aq)
(i) Identify the oxidising agent and the reducing agent in this reaction.
Oxidising agent ................................................................................................
Reducing agent .................................................................................................

(ii) Write a half-equation to show how sulphur dioxide is converted into sulphate ions in aqueous solution.
...........................................................................................................................
(3)

(c) Fe2+ ions are oxidised to Fe3+ ions by ions in acidic conditions. The ions are reduced to Cl– ions.
(i) Write a half-equation for the oxidation of Fe2+ ions in this reaction.
...........................................................................................................................

(ii) Deduce the oxidation state of chlorine in ions.
...........................................................................................................................

(iii) Write a half-equation for the reduction of ions to Cl– ions in acidic conditions.
...........................................................................................................................

(iv) Hence, write an overall equation for the reaction.
...........................................................................................................................
(4)

(Total 8 marks)

7. (a) In acidic conditions, hydrogen peroxide, H2O2, oxidises iodide ions to iodine. The hydrogen peroxide is reduced to water. In H2O2, oxygen has an oxidation state of –1.
(i) Construct a half-equation for the reduction of hydrogen peroxide to water in acidic conditions.
......................................................................................................................

(ii) Construct a half-equation for the oxidation of I– ions to iodine.
......................................................................................................................

(iii) Construct an equation for the overall reaction.
......................................................................................................................
(3)

(Total 12 marks)

8. Chlorine and bromine are both oxidising agents.
(a) Define an oxidising agent in terms of electrons.
.....................………………………………………………………………………….
(1)

(b) In aqueous solution, bromine oxidises sulphur dioxide, SO2, to sulphate ions,
(i) Deduce the oxidation state of sulphur in SO2 and in
SO2 ..........…………………………………………………………………….
…………………………………………………………………………

(ii) Deduce a half-equation for the reduction of bromine in aqueous solution.
...........………………………………………………………………………….

(iii) Deduce a half-equation for the oxidation of SO2 in aqueous solution forming and H+ ions.
...........………………………………………………………………………….

(iv) Use these two half-equations to construct an overall equation for the reaction between aqueous bromine and sulphur dioxide.
...........………………………………………………………………………….
(5)

(c) Write an equation for the reaction of chlorine with water. Below each of the chlorine-containing products in your equation, write the oxidation state of chlorine in that product.
.....................………………………………………………………………………….
.....................………………………………………………………………………….
(3)

(d) Give a reason why chlorine is not formed when solid potassium chloride reacts with concentrated sulphuric acid.
.....................………………………………………………………………………….
(1)

(e) Write an equation for the reaction between solid potassium chloride and concentrated sulphuric acid.
.....................………………………………………………………………………….
(1)

(f) Solid potassium bromide undergoes a redox reaction with concentrated sulphuric acid.
(i) Give the oxidation product formed from potassium bromide.
...........………………………………………………………………………….
(ii) Give the reduction product formed from sulphuric acid.
...........………………………………………………………………………….
(2)
(Total 13 marks)

9. (a) State the trend in the boiling points of the halogens from fluorine to iodine and explain this trend.
Trend ..........................................................................................................................
Explanation ................................................................................................................
.........................……….............................................................…...............................
.........................……….............................................................…...............................
(4)
(b) Each of the following reactions may be used to identify bromide ions. For each reaction, state what you would observe and, where indicated, write an appropriate equation.
(i) The reaction of aqueous bromide ions with chlorine gas
Observation ......................................................................................................
Equation ...........................................................................................................

(ii) The reaction of aqueous bromide ions with aqueous silver nitrate followed by the addition of concentrated aqueous ammonia
Observation with aqueous silver nitrate ..........................................................
Equation ...........................................................................................................
Observation with concentrated aqueous ammonia ..........................................
........................................................................................…...............................
(iii) The reaction of solid potassium bromide with concentrated sulphuric acid
Observation 1 ...................................................................................................
Observation 2 ...................................................................................................
(7)

(c) Write an equation for the redox reaction that occurs when potassium bromide reacts with concentrated sulphuric acid.
.....................................................................................................................................
(2)
(Total 13 marks)

10. (a) Describe and explain the trend in the boiling points of the elements down Group VII from fluorine to iodine.
(4)

(b) Describe what you would observe when aqueous silver nitrate, followed by dilute aqueous ammonia, is added to separate aqueous solutions of sodium chloride and sodium bromide.
(4)

(c) State the trend in the oxidising abilities of the elements down Group VII from chlorine to iodine.
Explain how this trend can be shown by displacement reactions between halogens and halide ions in aqueous solutions.
Illustrate your answer with appropriate observations and equations.
(7)
(Total 15 marks)

11. (a) Explain, by referring to electrons, the meaning of the terms reduction and reducing agent.
(2)

(b) Iodide ions can reduce sulphuric acid to three different products.
(i) Name the three reduction products and give the oxidation state of sulphur in each of these products.
(ii) Describe how observations of the reaction between solid potassium iodide and concentrated sulphuric acid can be used to indicate the presence of any two of these reduction products.
(iii) Write half-equations to show how two of these products are formed by reduction of sulphuric acid.
(10)

(c) Write an equation for the reaction that occurs when chlorine is added to cold water. State whether or not the water is oxidised and explain your answer.
(3)
(Total 15 marks)

12. (a) State the trend in electronegativity of the elements down Group VII. Explain this trend.
Trend ..........................................................................................................................
Explanation ................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(3)

(b) (i) State the trend in reducing ability of the halide ions down Group VII.
...........................................................................................................................

(ii) Give an example of a reagent which could be used to show that the reducing ability of bromide ions is different from that of chloride ions.
...........................................................................................................................
(2)

(c) The addition of silver nitrate solution followed by dilute aqueous ammonia can be used as a test to distinguish between chloride and bromide ions. For each ion, state what you would observe if an aqueous solution containing the ion was tested in this way.
Observations with chloride ions ..................................................................................
......................................................................................................................................
Observations with bromide ions ..................................................................................
......................................................................................................................................
(4)

(d) Write an equation for the reaction between chlorine and cold, dilute aqueous sodium hydroxide. Give two uses of the resulting solution.
Equation .......................................................................................................................
Use 1 .............................................................................................................................
Use 2 .............................................................................................................................
(3)
(Total 12 marks)

13. (a) Identify the halogen that is the strongest oxidising agent.
.....................................................................................................................................
(1)

(b) Give the formula of the halide ion that is the strongest reducing agent.
.....................................................................................................................................
(1)

(c) Describe what you would observe in each case when aqueous silver nitrate is added separately to dilute aqueous sodium fluoride and to dilute aqueous sodium iodide. Write an equation, including state symbols, for the reaction between aqueous sodium iodide and aqueous silver nitrate.
Observation with NaF(aq) .........................................................................................
Observation with NaI(aq) ..........................................................................................
Equation .....................................................................................................................
(3)

(d) Describe what you would observe when concentrated sulphuric acid is added to solid sodium chloride. Write an equation for the reaction that occurs.
Observation ................................................................................................................
Equation .....................................................................................................................
(2)

(e) Describe two observations that you would make when concentrated sulphuric acid is added to solid sodium iodide. Write an equation for a reaction that occurs in which iodide ions are oxidised by the sulphuric acid.
Observation 1 .............................................................................................................
Observation 2 .............................................................................................................
Equation .....................................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(4)

(f) Describe the colour change that you would observe when an aqueous solution of iodine, to which starch solution has been added, reacts with an excess of Na2S2O3. Write an equation for the reaction that occurs between iodine and Na2S2O3.
Observation ................................................................................................................
Equation .....................................................................................................................
(3)
(Total 14 marks)

14.
(a) State and explain the trend in electronegativity down Group VII from fluorine to iodine.
Trend ...........................................................................................................................
Explanation ..............................................................................................................
.....................................................................................................................................
.....................................................................................................................................
(3)

(b) State what you would observe when chlorine gas is bubbled into an aqueous solution of potassium iodide. Write an equation for the reaction that occurs.
Observation ..............................................................................................................
Equation ...................................................................................................................
(2)

(c) Identify two sulphur-containing reduction products formed when concentrated sulphuric acid oxidises iodide ions. For each reduction product, write a half-equation to illustrate its formation from sulphuric acid.
Reduction product 1 .................................................................................................
Half-equation ...........................................................................................................
Reduction product 2 .................................................................................................
Half-equation ...........................................................................................................
(4)

(d) Write an equation for the reaction between chlorine gas and dilute aqueous sodium hydroxide. Name the two chlorine-containing products of this reaction and give the oxidation state of chlorine in each of these products.
Equation ...................................................................................................................
Name of product 1 ......................................................................................................
Oxidation state of chlorine in product 1 ...............................................................
Name of product 2 ......................................................................................................
Oxidation state of chlorine in product 2 ...............................................................
(5)
(Total 14 marks)

16.
(a) State and explain the trend in electronegativity down Group VII from fluorine to iodine.
Trend ......................................................................................................................
Explanation ............................................................................................................
................................................................................................................................
(3)

AQA chemistry unit 2

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