ASChemistryOCRExam Questions3. Periodic Table & Energy3.3 The Halogens

The Halogens (OCR AS Chemistry)

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3.3 The Halogens

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3.3 The Halogens

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11 mark

A student adds aqueous sodium carbonate to one test tube and aqueous silver nitrate to a second test tube. The student adds dilute sulfuric acid to each test tube.

Which row has the correct observations?

   Aqueous sodium carbonate Aqueous silver nitrate 
A  no change  precipitate
B  no change  no change
C  effervescence  no change
D effervescence   precipitate

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    21 mark

    The halogens exist as diatomic molecules, X2.

    Which statement is correct?

    • The boiling points of the halogens decrease down the group

    • The oxidising power of the halogens increases down the group

    • The electronegativity of X increases down the group

    • The number of electrons in each X2 molecule increases down the group

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    31 mark

    A student compares the properties of chlorine, iodine and their compounds.

    Property X for iodine is bigger than for chlorine.

    What is property     X?

    • Solubility of the silver halide in dilute NH3 (aq)

    • Reducing ability of the element

    • Strength of C-X bond

    • Oxidising ability

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    41 mark

    What is the correct observation when cyclohexane is added to a solution containing potassium iodide and chlorine water?

    • The cyclohexane layer appears colourless

    • The cyclohexane layer appears orange - brown

    • The cyclohexane layer appears purple

    • The cyclohexane layer appears pale green

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    51 mark

    Which of these anions forms a white precipitate when tested with acidified silver nitrate solution?

    • CO32-

    • SO42-

    • OH –

    • Cl –

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    61 mark

    Which of the following statements about hydrogen halides, HX, is not correct?

    • The bond length of the H-X bonds increase down the group 

    • The reaction between fluorine and hydrogen is explosive

    • Hydrogen fluoride can form hydrogen bonds

    • The reaction between bromine and hydrogen is a vigorous reaction

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    71 mark

    Why does the oxidising power of the halogens decrease as the group is descended?

    • Shielding increases down the group therefore it is more difficult to accept an extra electron

    • Atomic radius decreases down the group 

    • Shielding increases down the group therefore it is easier to donate an electron

    • The halogens become more electronegative down the group

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    81 mark

    What is the correct chemical test and observation for the presence of an iodide ion?

      Chemical test Observation
    A Acidified silver nitrate Yellow precipitate insoluble in concentrated ammonia
    B Acidified barium chloride White precipitate insoluble in hydrochloric acid
    C Acidified potassium nitrate Yellow precipitate insoluble in concentrated ammonia
    D Bromine water Brown solution changes to colourless solution

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      91 mark

      A student added a solution of bromine to a solution of sodium iodide.

      Which statement is not correct?

      • The iodide ions are oxidised

      • Bromine is reduced

      • Bromine acts as the reducing agent

      • A brown solution is observed

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      101 mark

      Chlorine is used to treat drinking water. 

      Which statement is correct?

      • Water reacts with chlorine to form hydrochloric acid and chloric(I) acid, HClO

      • When universal indicator is added to chloric(I) acid, HClO it turns blue then white

      • Chloric acid does not dissociate further when added to water

      • Chlorine reacts with cold sodium hydroxide to form sodium chloride and water only

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      11 mark

      Which pair of solutions forms a white precipitate?

      • NH4Cl (aq) and NaOH (aq)

      • KBr (aq) and AgNO3 (aq)

      • FeCl3 (aq) and NH3 (aq)

      • Cr2(SO4)3 (aq) and BaCl2 (aq)

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      21 mark

      What is the best explanation for the trend in boiling points down the halogens group?

      • The covalent bonds become stronger.

      • The hydrogen bonds become stronger.

      • The permanent dipole–dipole interactions become stronger.

      • The induced dipole–dipole interactions (London forces) increase.

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      31 mark

      Which silver compound is insoluble in concentrated NH3 (aq)?

      • AgNO3

      • AgCl

      • AgBr

      • AgI

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      4
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      The chemistry of the Group 7 elements often involves redox processes. 

      Which of the following statements is correct?

      • In reactions with water in the absence of sunlight, chlorine is oxidised and reduced simultaneously

      • Iodide ions are the strongest oxidising agent of the first four Group 7 ions

      • Iodine can oxidise bromide ions

      • Fluorine is a weaker oxidising agent than chlorine

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      51 mark

      A student analysed a solution containing a halide ion which was kept in an unlabelled bottle in the laboratory. Their tests and observations were recorded in the table below.

      Test

      Chemical test

      Observation 

      1

      Addition of chlorine water and cyclohexane

      Organic layer colour change from colourless to brown

      2

      Addition of hydrochloric acid and silver nitrate

      Off-white precipitate 

      Give the most likely halide ion or combination of halide ions present in the solution from the student’s results. 

      • Iodide and bromide

      • Iodide

      • Chloride

      • Bromide

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      61 mark

      Which is the correct equation for the reaction of cold, dilute aqueous sodium hydroxide, NaOH, and chlorine, Cl2?

      • Cl2 + 2NaOH → NaCl + NaClO + H2O

      • ½ Cl2 + 2OH- → ClO- + H2O + e-

      • ½ Cl2 + 6OH- → ClO3- + 3H2O + e-

      • 3Cl2 + 6NaOH → 3NaCl + 3NaClO3 + H2O

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      71 mark

      Which statement about the reactions of halogens with halide ions is correct?

      • Br2 (aq) can oxidise Cl− (aq).

      • Br2 (aq) can reduce I− (aq).

      • I− (aq) can reduce Cl2 (aq).

      • Br− (aq) can oxidise I2 (aq).

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      81 mark

      2-chloropropane, 2-bromopropane and 2-iodopropane are reacted separately with aqueous potassium hydroxide and acidified silver nitrate. 

      The reaction containing 2-iodopropane produces a precipitate the quickest.

      Which statement explains this most accurately?

      • The C-I bond has the greatest bond enthalpy.

      • The C-Cl bond is the least polar and therefore weakest

      • The C–I bond has a C atom with the greatest δ+ charge.

      • The C–I bond requires the least energy to break.

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      91 mark

      Which reaction is not an example of a disproportionation reaction?

      • Cl2 + H2O → HCl + HClO

      • 2ClO2 + 2NaOH → NaClO2 + NaClO3 + H2O

      • 4KClO3 → 3KClO4 + KCl

      • MnO2 + 4HCl → MnCl2 + Cl2 + 2H2O

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      101 mark

      The following report appeared in a newspaper:

      Barrels of bromine broke open after a vehicle collision on the motorway. Traffic was diverted as brown, bromine gas drifted over the surface of the road (as bromine is less dense than air), causing irritation to drivers’ eyes. Firemen sprayed water over the scene of the accident, dissolving the bromine and washing it away.

      Which of the following observations is incorrect in the report?

      • bromine is not brown

      • bromine does not vaporise readily

      • bromine is less dense than air

      • bromine does not dissolve in water

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      11 mark

      Which statement(s) about the reaction of chlorine and water is/are correct?

      1. Chlorine reacts with water in a disproportionation reaction to produce a solution with a high pH.
      2. If the water is kept slightly above pH 7, the concentrations of the products will decrease.
      3. When HClO kills the bacteria in the water the equilibrium will shift to the right.

      • 1, 2 and 3

      • Only 1 and 2

      • Only 2 and 3

      • Only 1

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      21 mark

      A student carries out an experiment to test for halide ions in an unknown solution. They use the following method:

      Step 1: Add excess AgNO3 (aq) to the solution

      Step 2: Filter, wash, dry and record the mass of the pale yellow precipitate produced

      Step 3: Add excess dilute ammonia to the dry precipitate

      Step 4: Filter, wash, dry and record the mass of the darker yellow precipitate

      Which statement(s) is/are correct?

      1. The second mass recorded will be less than the first which shows that the solution contains chloride ions.
      2. Before step 1, hydrochloric acid should be added to acidify the solution and prevent a false positive.
      3. The precipitate in step 4 contains pure silver iodide. 

      • 1, 2 and 3

      • Only 1 and 2

      • Only 2 and 3

      • Only 1

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      31 mark

      Which statement about Group 7 elements is not correct?

      • Fluorine is the weakest reducing agent in Group 7.

      • The bond dissociation energy of the hydrogen halides from HCl to HI increases.

      • CH3I would produce a silver halide precipitate with acidified AgNO3 faster than CH3Cl or CH3Br.

      • Astatine has a lower first ionisation energy than iodine.

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      41 mark

      Pairs of compounds are tested using simple test tube reactions to distinguish between them. The pairs of compounds, reagents used and observations with each compound are recorded below.

      Which row is correct?

       

      Compounds

      Reagent

      Observation with compound 1

      Observation with compound 2

      A
      1. Na2CO3
      2. BaCl2

      H2SO4

      Cloudy

      White precipitate

      B
      1. NaCl
      2. NH4I

      Acidified AgNO3

      White precipitate

      Cream precipitate

      C
      1. Na2CO3
      2. NH4Cl

      NaOH followed by litmus paper

      No change

      Turns red litmus paper blue

      D
      1. BaCl2
      2. NH4Cl

      HCl

      White precipitate

      No change

       

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        51 mark

        Which of the following statement(s) is/are correct?

        1. The white solid, AgCl, gives a white precipitate when added to acidified silver nitrate which will dissolve in dilute ammonia.
        2. Bromine liberates iodine from aqueous potassium iodide to produce a brown solution.
        3. Chlorine is a better oxidising agent than chloride ions, iodine and iodide ions.

        • 1, 2 and 3

        • Only 1 and 2

        • Only 2 and 3

        • Only 1

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