Group 7 exam questions Flashcards by eva coopere

Chlorine has a low boiling point because the forces between the molecules
are weak.
Explain how these forces arise between molecules of chlorine.
3 marks

1- Random movement of electrons in one molecule creates a dipole/ a temporary dipole is formed in one molecule / an imbalance in electron density in one molecule
2- Induces a dipole in a neighbouring molecule.
3-These temporary dipoles attract / temporary attraction between δ+ and δ–

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Give an equation for the reaction of chlorine with water.
Give a reason why chlorine is added to drinking water.
Equation-
Reason -
2 marks

Cl2 + H2O ⇌ HCl + HClO / 2 Cl2 + 2 H2O → 4 HCl + O2
Kills bacteria / kills microorganisms / kills microbes / kills pathogens
Allow sterilise water / disinfect water

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Chlorine reacts with cold, aqueous sodium hydroxide in the manufacture of
bleach.
Give an equation for this reaction. 1 mark

Cl2 + 2 NaOH → NaCl + NaClO + H2O

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Which pair of solutions, when mixed, reacts to form a dark brown solution?
A NaF(aq) + Cl2(aq)
B NaCl(aq) + Br2(aq)
C NaBr(aq) + Cl2(aq)
D NaI(aq) + Br2(aq)

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Some solid sodium halides are reacted with concentrated sulfuric acid.
Which solid sodium halide does not produce a sulfur-containing gas as one of the products?
A NaCl
B NaBr
C NaI
D NaAt

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Give an equation for the reaction of solid sodium bromide with
concentrated sulfuric acid to form bromine.
State one observation made during this reaction.
2 marks

3H2SO4 + 2NaBr → 2NaHSO4 + SO2 + Br2 + 2H2O
orange/brown fumes/solution

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A solution that is thought to contain chloride ions and iodide ions is tested.
1. Dilute nitric acid is added to the solution.
2. Aqueous silver nitrate is added to the solution.
3. A pale yellow precipitate forms.
4. Excess dilute aqueous ammonia is added to the mixture.
5. Some of the precipitate dissolves and a darker yellow precipitate
remains.
Give a reason for the use of each reagent.
Explain the observations.
Give ionic equations for any reactions.

HNO3 removes (hydroxide/carbonate) ions that may give other ppts with AgNO3
AgNO3 produces ppts with chloride/iodide/halide CANT SAY HALOGEN SAY HALIDE
not chlorine/iodine/halogen
Ag+ (aq) + Cl− (aq) → AgCl(s) OR
Ag+(aq) + I− (aq) → AgI(s)
NH3 dissolves AgCl (leaving yellow AgI)
allow chloride/iodide salt/ppt
AgCl(s) + 2NH3(aq) → Ag(NH3)2
+ (aq) + Cl− (aq)
precipitate reacts with the dilute ammonia solution

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Chlorine is used to treat water even though it is toxic to humans.
Give one reason why water is treated with chlorine.
Explain why chlorine is added to water even though it is toxic.
Give an equation for the reaction of chlorine with cold water.

Reason: kills bacteria
Explanation: HEALTH benefits of adding chlorine outweighs the toxic effects
Eq- Cl2(aq)+ H2O(aq)= HClO(aq)+ HCl(aq)
Reversible reaction

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Solid sodium iodide reacts with concentrated sulfuric acid to form iodine
and sulfur in a redox reaction.
Give a half-equation to show the conversion of iodide ions to iodine.
Give a half-equation to show the conversion of sulfuric acid to sulfur.
Give an overall equation for this redox reaction.
Identify one other sulfur-containing reduction product formed when solid
sodium iodide reacts with concentrated sulfuric acid.

2I– → I2 + 2e-
H2SO4 + 6H+ + 6e- → S + 4H2O
6H+ + 6I- + H2SO4 → 3I2 + S + 4H2O
SO2 or H2S

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Which property increases down Group 7?
A ability to oxidise a given reducing
agent
B boiling point
C electronegativity
D first ionisation energy

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Which equation shows a redox reaction that does not occur?
A Br2(aq) + 2 KI(aq) → I2(aq) + 2 KBr(aq)
B Cl2(g) + 2 KI(aq) → I2(aq) + 2 KCl(aq)
C Cl2(g) + 2 KBr(aq) → Br2(aq) + 2 KCl(aq)
D I2(aq) + 2 KBr(aq) → Br2(aq) + 2 KI(aq)

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State what is observed when silver nitrate solution is added to sodium
fluoride solution.

No reaction/ no visible change

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State one observation when solid sodium chloride reacts with concentrated
sulfuric acid.
Give an equation for the reaction.
State the role of the chloride ions in the reaction.

Steamy white fumes of HCl evolve
NaCl(s) + H2SO4(l) = NaHSO4(s)+HCl(g)
Acts as a base/ proton acceptor because the sulfuric acid acts as an acid

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Give an equation for the redox reaction between solid sodium bromide and
concentrated sulfuric acid.
Explain, using oxidation states, why this is a redox reaction.

2Br- + 2H+ + H2SO4 → SO2 + Br2 + 2H2O
This is the redox equation that takes place after the acid base reaction
Br changes oxidation state from −1 to 0 and is oxidised
S changes oxidation state from +6 to +4 and is reduced

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State what is observed when aqueous chlorine is added to sodium bromide
solution.
Give an ionic equation for the reaction.

Yellow solution
2Br-+ Cl2= 2Cl-+ Br2

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Which shows the major product(s) formed when chlorine reacts with cold, dilute,
aqueous sodium hydroxide?
A NaCl only
B NaClO only
C NaCl and NaClO
D NaCl and NaClO3

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What is the best oxidising agent?
A F2
B F–
C I2
D I

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Which statement is correct about reactions involving halide ions?
A Sodium chloride forms chlorine when added to
concentrated sulfuric acid.
B Sodium chloride forms chlorine when added to
bromine.
C Sodium bromide forms bromine when added to
concentrated sulfuric acid.
D Sodium bromide forms bromine when added to iodine.

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Which statement is not correct about the trends in properties of the hydrogen
halides from HCl to HI ?
A The boiling points decrease.
B The bond dissociation energy of H−X decreases.
C The polarity of the H−X bond decreases.
D They are more easily oxidised in aqueous solutions.

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Solid sodium chloride reacts with concentrated sulfuric acid.
Give an equation for this reaction.
State the role of the sulfuric acid in this reaction.

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NaCl(s)+ H2SO4(l)= NaHSO4(S)+ HCl(g)
Proton donor

Fumes of sulfur dioxide are formed when sodium bromide reacts with
concentrated sulfuric acid.
For this reaction
* give an equation
* give one other observation
* state the role of the sulfuric acid.

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2 H+ + 2 Br – + H2SO4 → SO2 + Br2 + 2 H2O
brown gas or brown fumes or orange gas or orange fumes
Oxidising agent

Chlorine reacts with hot aqueous sodium hydroxide as shown in the
equation.
3 Cl2 + 6 NaOH → NaClO3 + 5 NaCl + 3 H2O
Give the oxidation state of chlorine in NaClO3 and in NaCl
State, in terms of redox, what happens to chlorine in the reaction in part
(c).

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+5 and -1
Oxidised and reduced( disproportionation)

Give the ionic equation for the formation of Ag2CO3

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2 Ag+ + CO32–→ Ag2CO3

Separate unlabelled solid samples of three anhydrous sodium compounds are
provided for a student to identify.
These compounds are known to be sodium carbonate, sodium fluoride and
sodium chloride but it is not known which sample is which.
Outline a logical sequence of test-tube reactions that the student could carry out
to identify each of these compounds.
Include the observations the student would expect to make.
Give equations, including state symbols, for any reactions that would take
place. 6 marks

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Stage 1 Suggested tests
1a Add named acid to all 3
1b Add water / make into a solution
1c Add AgNO3
Ignore addition of NH3 / Ignore additional test for CO2 produced
Stage 2 Expected observations - conclusions
2a Na2CO3 will fizz with acid
2b NaCl gives white ppt with AgNO3
2c NaF shows no (visible) change / no ppt
Stage 3 Equations – state symbols must match method
3a Na2CO3 + 2HNO3 → 2NaNO3 + CO2 + H2O … or ionic
3b AgNO3 + NaCl → AgCl + NaNO3
… or ionic
3c correct state symbols

Which statement is correct about the reaction between concentrated sulfuric acid and solid sodium bromide? A Bromide ions are reduced. B Hydrogen bromide and sulfur are formed. C Sulfuric acid acts as an oxidising agent. D Bromine and hydrogen sulfide are formed.

Which is the best technique to remove the silver chloride that forms when aqueous solutions of silver nitrate and sodium chloride react? A Refluxing B Evaporation C Filtration D Distillation

Which statement about astatine is correct? A Astatine has a greater electronegativity than bromine B Astatine is a better oxidising agent than bromine C Astatine has a greater boiling point than bromine D Astatine has a greater first ionisation energy than bromine

Which species is not produced by a redox reaction between solid sodium iodide and concentrated sulfuric acid? A Na2SO4 B H2S C S D SO2

A student was given a 50.0 g sample of solid silver chloride contaminated with solid silver carbonate. The student suggested the following method to obtain the maximum amount of pure dry silver chloride from the sample: 1. Tip the solid into a boiling tube. 2. Add dilute nitric acid. 3. Allow the remaining solid to settle. 4. Decant off the liquid. 5. Leave the sample to dry on a shelf. Identify any faults or omissions in the method suggested by the student. Suggest improvements to the method, using commonly available laboratory equipment.

Indicative Chemistry content Stage 1 Apparatus * Boiling tube likely to be too small for 50.0 g solid plus acid * Use a (large / medium / 250 ml) beaker instead Stage 2 AgCl Prep * HNO3 will form soluble AgNO3 so max AgCl not obtained * Use HCl instead * Method doesn’t say how much acid should be used Or Use excess acid / Add acid until no more bubbles evolved Stage 3 Making pure dry solid * Decanting means solid wet / contaminated with HNO3 / acid or decanting means some solid lost * Instead use filter and then wash with distilled water (and then dry)

(a) Bromine (Br2), strontium chloride (SrCl2) and iodine monochloride (ICl) all have similar Mr values. Suggest, with reasons, the order of melting points for these three substances. 6 marks

SrCl2 then ICl then Br2 SrCl2 is an ionic compound, has strong ionic bonds with strong electrostatic forces of attraction between oppositley charged ions Has a lattice so many strong bonds to overcome ICl has dipole dipole forces due to the molecule being polar due to a difference in electronegativity, this is weaker than ionic bonds Br2 has van deer waals between molecules which are much weaker

Write an equation for the reaction of chlorine with cold water. State a reason why chlorine is added to drinking water, and suggest a disadvantage of treating water in this way.

Cl2 + H2O ⇌ HCl + HClO Kills bacteria Wasteful as most potable water not used for drinking - used in washing clothes etc OR Some people suffer eye irritation / Some people find the taste unpleasant OR can react with organic compounds to produce harmful substances

Which equation represents a reaction that does take place? A Cl2 + 2NaI ⟶ 2NaCl + I2 B Br2 + 2NaCl ⟶ 2NaBr + Cl2 C NaCl + H2O ⟶ HCl + NaOH D 2HCl + H2SO4 ⟶ Cl2 + SO2 + 2H2O

Which species is the best oxidising agent? A Cl2 B Cl− C Br 2 D Br−

Sodium bromide reacts with concentrated sulfuric acid in a different way from sodium chloride. Write an equation for this reaction of sodium bromide and explain why bromide ions react differently from chloride ions.

2NaBr + 2H2SO4 Na2SO4 + Br2 + SO2 + 2H2O Br– ions are bigger than Cl– ions Therefore Br– ions more easily oxidised / lose an electron more easily than Cl– ions

A colourless solution contains a mixture of sodium chloride and sodium bromide. Using aqueous silver nitrate and any other reagents of your choice, develop a procedure to prepare a pure sample of silver bromide from this mixture. Explain each step in the procedure and illustrate your explanations with equations, where appropriate.

Stage 1: formation of precipitates * Add silver nitrate * to form precipitates of AgCl and AgBr * AgNO3 + NaCl → AgCl + NaNO3 * AgNO3 + NaBr → AgBr + NaNO3 Stage 2: selective dissolving of AgCl * Add excess of dilute ammonia to the mixture of precipitates * the silver chloride precipitate dissolves * AgCl + 2NH3 → Ag(NH3)2 + + Cl− Stage 3: separation and purification of AgBr * Filter off the remaining silver bromide precipitate * Wash to remove soluble compounds * Dry to remove water

Write an ionic equation for the reaction between chlorine and cold dilute sodium hydroxide solution. Give the oxidation state of chlorine in each of the chlorine-containing ions formed.

Cl2 + 2HO– OCl– + Cl– + H2O OCl– is +1 Cl– is –1

Group 7 exam questions Flashcards

(37 cards)