Exam code: 7405
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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A scientist 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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When chlorine reacts with cold sodium hydroxide the following reaction occurs
Cl2 (aq) + 2NaOH (aq) → NaCl (aq) + NaClO (aq) + H2O (l)
Which of the following statements is correct?
The chlorine has only been oxidised
The oxidation number of Cl in NaClO is 0
The chlorine is simultaneously oxidised and reduced
The oxidation number of Cl in Cl2 is -1
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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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When chlorine reacts with hot sodium hydroxide the following reaction occurs.
3Cl2 (g) + 6NaOH (aq) → 5NaCl (aq) + NaClO3 (aq) + 3H2O (l)
Which row shows the correct oxidation state of chlorine in each ion?
| Cl2 | NaCl | NaClO3 |
A B C D | 0 0 0 0 | -1 +1 +1 -1 | +5 -5 -3 +3 |
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What are the correct observations for the reaction of solid sodium bromide and concentrated sulfuric acid?
White fumes
Reddish brown gas and yellow solid produced
Yellow solid produced
Reddish-brown gas and pungent odour
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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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Which of the following equations involving chlorine is not correct?
Cl2 (aq) + H2O (l) → HCl (aq) + HClO (aq)
Cl2 (aq) + 2KBr (aq) → 2KCl (aq) + Br2 (aq)
HClO (aq) ⇌ H+ (aq) + ClO- (aq)
I2 (aq) + 2KCl (aq) → 2KI (aq) + Cl2 (aq)
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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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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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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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Which list of the products from the reaction of potassium bromide with concentrated sulfuric acid is correct?
potassium hydrogensulfate, sulfur, hydrogen bromide, bromine and water
potassium hydrogen sulfate, hydrogen bromide, bromine, water and sulfur dioxide
potassium hydrogen sulfate, hydrogen bromide and bromine
potassium hydrogen sulfate, hydrogen bromide and hydrogen sulfide
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Which graph correctly illustrates a trend found in Group 7?
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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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When sulfuric acid and sodium iodide react, one of the reactions that takes place is shown by the equation below:
8NaI + 9H2SO4 → 8NaHSO4 + 4I2 + H2S + 4H2O
Which species has been oxidised in this reaction?
H+
S
Na+
I-
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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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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. 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-Br bond is more polar that the C-I bond
The C-Cl bond is the most polar and therefore strongest
The C-Cl bond is the shortest
The C-I bond is the longest
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Which is the correct equation for the reaction of hot, dilute aqueous sodium hydroxide, NaOH, and chlorine, Cl2?
Cl2 + 2NaOH → NaCl + NaClO + H2O
Cl2 + 2OH- → ClO- + H2O + e-
Cl2 + 6OH- → ClO3- + 3H2O + e-
3Cl2 + 6NaOH → 3NaCl + 3NaClO3 + H2O
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What is the change in oxidation state of sulfur in the following reaction:
8KI + 5H2SO4 → 4K2SO4 + H2S + 4I 2 + 4H2O
6
8
10
4
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Why does the electronegativity of the halogens decrease down Group 7?
The atomic radii of the halogens decrease down the group. Therefore, the outer shell is further away from the nucleus so the oxidising power of the halogens decreases.
The atomic radii of the halogens increase down the group. Therefore the outer shell is further away from the nucleus so the ability to accept an electron decreases.
The atomic radii of the halogens increase down the group. Therefore the outer shell is further away from the nucleus so the reducing ability decreases.
The atomic radii of the halogens increases down the group. Therefore, the outer shell is further away from the nucleus so the oxidising power of the halogens increases.
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Which of the following is the best oxidising agent?
Cl-
Br2
Br-
Cl2
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Which of the following statements is not correct?
Silver bromide is soluble in concentrated ammonia
Bromine is liberated when chlorine is added to sodium bromide
Sulfur dioxide is produced when solid sodium chloride is added to concentrated sulfuric acid
A purple colour can be observed when solid sodium iodide is added to concentrated sulfuric acid
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Astatine is a halogen which is found at the bottom of Group 7.
Solid sodium astatide, NaAt reacts in a similar way as sodium iodide, NaI when added to concentrated sulfuric acid.
What are some of the possible redox products formed in this reaction?
| Na2SO4 | SO2 | At2 | HAt | H2S |
A | ⨯ | ✓ | ✓ | ⨯ | ✓ |
B | ✓ | ✓ | ✓ | ✓ | ✓ |
C | ✓ | ✓ | ⨯ | ⨯ | ✓ |
D | ⨯ | ✓ | ⨯ | ✓ | ⨯ |
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Hydrogen halides, H-X, are formed from the reaction of hydrogen and a halogen, X2. Which of the following statements correctly explains why HBr (aq) is a stronger acid than HF (aq)?
HF (aq) releases more H+ ions
HF dissociates more readily than HBr when dissolved in solution
The H-Br bond has the greatest bond dissociation energy
The H-F bond is stronger so does not break as easily
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Chloric acid, HClO3, is a strong acid and can be prepared by the following reaction.
Ba(ClO3)2 (aq) + H2SO4 (aq) → BaSO4 (s) + 2HClO3 (aq)
What is the overall change in oxidation state of chlorine?
0
+1
+2
+3
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What is the reducing agent in this reaction?
Br- + 3HClO + 3OH- → BrO3- + 3Cl- + 3H2O
OH-
HClO
Br-
BrO3-
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Chlorine gas can be prepared by oxidising concentrated hydrochloric acid with potassium permanganate. This reaction is carried out in a fume hood.
___HCl + ___KMnO4 → ___Cl2 + ___KCl + ___MnCl2 + ___H2O
Which whole number stoichiometric coefficients are correct to balance the equation?
| HCl | KMnO4 | Cl2 | KCl | MnCl2 | H2O |
A | 8 | 2 | 3 | 4 | 4 | 2 |
B | 8 | 2 | 3 | 2 | 2 | 4 |
C | 16 | 4 | 5 | 4 | 2 | 8 |
D | 16 | 2 | 5 | 2 | 2 | 8 |
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Which of the following equations occurs between concentrated sulfuric acid and solid potassium bromide is correct
Br2 + 2e- → 2Br-
H2SO4 + 2HBr → Br2 + SO2 + 2H2O
SO42- + 10H+ + 8e- → H2S + 4H2O
H2SO4 + 6HBr → 3Br2 + S + 4H2O
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A few drops of sodium chlorate (I) solution is added to potassium bromide solution. A red-brown gas is produced along with sodium chloride solution.
Which of the following statements is correct?
The oxidation state of chlorine in NaClO is +5
Chlorine gas is produced
Bromide ions are oxidised in this reaction
NaClO is the reducing agent
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Which species is the strongest reducing agent?
Cl2
Br2
Cl-
Br-
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