3.2.3 Group 7 PPQs Flashcards
What is observed when this reaction occurs?: Ag+(aq) + Cl-(aq) -> AgCl(aq)
white precipitate
What is the balanced equation for the reaction between AgCl and NH3?
Chlorine has a low boiling point because the forces between the molecules are weak. Explain how these forces arise between molecules of chlorine
- Random movement of electrons in one molecule creates a temporary dipole
- Induces a dipole in a neighbouring molecule.
- temporary dipoles attract
Chlorine reacts with cold, aqueous sodium hydroxide in the manufacture of bleach. Give an equation for this reaction.
Cl2 + 2 NaOH → NaCl + NaClO + H2O
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)
D: NaI(aq) + Br2(aq)
Give an equation for the reaction of solid sodium bromide with concentrated sulfuric acid to form bromine.
2H2SO4 + 2NaBr → Na2SO4 + SO2 + Br2 + 2H2O
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.
- HNO3 removes hydroxide/carbonate ions that may give other ppts with AgNO3
- AgNO3 produces ppts with chloride/iodide/halide
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.
Explain the observations.
- AgNO3 produces ppts with chloride/iodide/halide
- NH3 dissolves AgCl (leaving yellow AgI)
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 ionic equations for any reactions.
- Ag+(aq) + Cl−(aq) → AgCl(s)
- Ag+(aq) + I−(aq) → AgI(s)
- AgCl(s) + 2NH3(aq) → Ag(NH3)2+(aq) + Cl−(aq)
A student completes an experiment to determine the percentage by mass of sodium chloride in a mixture of sodium chloride and sodium iodide.
The student uses this method:
* 600 mg of the mixture are dissolved in water to form a solution.
* An excess of aqueous silver nitrate is added to the solution. This forms a precipitate containing silver chloride and silver iodide.
* Excess dilute ammonia solution is then added to the precipitate. The silver chloride dissolves.
* The silver iodide is filtered off from the solution, and is then washed and dried.
The mass of the silver iodide obtained is 315 mg
1. Suggest why an excess of silver nitrate is used.
2. Calculate the amount, in moles, of silver iodide obtained. Mr (AgI) = 234.8
3. Calculate the mass, in grams, of sodium iodide in the mixture. Mr (NaI) = 149.9
4. Calculate the percentage by mass of sodium chloride in the mixture.
- To ensure that all the halide ions (chloride and iodide) are removed from the solution / to ensure that all the halide ions precipitate out of solution
- 1.34 x 10–3 moles
- 0.201g
- 66.5%
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.
- Misty or steamy fumes
- NaCl + H2SO4 → NaHSO4 + HCl
- Base
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.
- 2NaBr + 2H2SO4 → Na2SO4 + Br2 + SO2 + 2 H2O
- Br changes oxidation state from −1 to 0 and is oxidised
- S changes oxidation state from +6 to +4 and is reduced
State what is observed when aqueous chlorine is added to sodium bromide solution.
Give an ionic equation for the reaction.
- orange solution
- Cl2 + 2 Br – → 2 Cl – + Br2
What is the best oxidising agent?
A F2
B F–
C I2
D I
A
give an Equation to show the reaction of AgBr and NH3
AgBr + 2NH3 -> Ag(NH3)2+ + Br-
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.
The following chemicals are also available:
distilled water, dilute solutions of NaOH, NH3, HCl, H2SO4
Stage 1 Apparatus
* Boiling tube likely to be too small for 50.0 g solid plus acid
* Use a large beaker instead
Stage 2 AgCl Prep
* HNO3 will form soluble AgNO3 so max AgCl not obtained
* Use HCl instead
* Use excess acid / Add acid until no more
bubbles evolved
Stage 3 Making pure dry solid
* Decanting means solid wet / contaminated with HNO3
* Instead use filter and then wash with distilled water and then dry
This question is about elements in Group 7 of the Periodic Table and their compounds. 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.
- SrCl2> ICl > Br2
- SrCl2 strong ionic bonds and Lattice so many strong bonds to overcome
- ICl has dipole-dipole between molecules – weaker than ionic bonds
- Br2 has van der Waals forces between molecules – much weaker
State a reason why chlorine is added to drinking water, and suggest a disadvantage of treating water in this way.
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
Bromine reacts with phosphorus to form phosphorus tribromide. Write an equation for this reaction
6Br2 + P4 ⟶ 4PBr3
This question is about the chemical properties of chlorine, sodium chloride and sodium bromide. Sodium bromide reacts with concentrated sulfuric acid in a different way
from sodium chloride. explain why bromide ions react differently from chloride ions.
Br– ions are bigger than Cl– ions. Therefore Br– ions more easily oxidised / lose an electron more easily than Cl– ions
Write an ionic equation for the reaction between chlorine and cold dilute sodium hydroxide solution.
Cl2 + 2HO– -> OCl– + Cl– + H2O
