Chemistry: Group 7 Part 2
This flashcard set covers key properties and reactions of sulphur and hydrogen sulphide, including their oxidation states and diagnostic tests. It also explains the redox behavior of halide ions when sulphuric acid is reduced, highlighting the oxidation of halide ions to halogen molecules.
oxidation number of sulphur in its element
0
Key Terms
oxidation number of sulphur in its element
0
test for sulphur
yellow solid
oxidation number of sulphur in hydrogen sulphide
-2
test for hydrogen sulphide
lead acetate paper: white > black
what happens to the halide ion if sulphuric acid is reduced by it
it will be oxidised to the halogen molecule X2
2X- > X2 + 2e-
method to react halide on with sulphuric acid
put 0.1g solid halide compound in test tub
add 10 drops conc. sulphuric
warm if necessary
iden...
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| Term | Definition |
|---|---|
oxidation number of sulphur in its element | 0 |
test for sulphur | yellow solid |
oxidation number of sulphur in hydrogen sulphide | -2 |
test for hydrogen sulphide | lead acetate paper: white > black |
what happens to the halide ion if sulphuric acid is reduced by it | it will be oxidised to the halogen molecule X2 2X- > X2 + 2e- |
method to react halide on with sulphuric acid |
|
initial observations NaCl + sulphuric | white fumes (HCl made) |
subsequent observations NaCl + sulphuric | no further change |
initial observation: NaBr + sulphuric | white fumes (HBr) |
subsequent observations: NaBr + sulphuric | brown fumes (Br2) SO2 detected |
initial observation: NaI + sulphuric | white fumes (HI) |
subsequent observations: NaI + sulphuric | purple fumes (I2) SO2,S, H2S all detected |
what is the initial observation in all halide ion and sulphuric acid reactions | white fumes |
what are the white fumes | the hydrogen halide as a gas |
why is NaCl + H2SO4 not a redox reaction |
| - example of proton transfer ie acid/base reaction |
why is there no further reaction between HCl produced and sulphuric acid | chloride ion cannot reduce sulphuric acid |
why can halides act as reducing agents | they are able to lose electrons to form the respective halogen |
what is the trend in reducing strength down the group of halides | increases |
why does reducing strength of halides increase down group | -they become less good at holding onto their electrons (size increases, attraction on outer electrons decreases) |
strongest oxidising agent group 7 | flourine |
strongest reducing agent group 7 | iodide |
test for halide ions |
|
Cl- PPT colour | white |
name and formula of PPT that Cl- forms | silver chloride AgCl |
Br- PPT colour | crea |
name and formula of PPT that Br- forms | silver bromide AgBr |
I- PPT colour | yellow |
name and formula of PPT that I- forms | silver iodide AgI |
why do F- ions not form a ppt with silver nitrate | silver fluoride is soluble in water |
Overall equation silver nitrate and sodium chloride | AgNO3 + NaCl > AgCl + NaNO3 |
Ionic equation silver nitrate + sodium chloride | Ag + Cl > AgCl |
General ionic equation for test for halide ions | Ag + X > AgX |
How to test for trends in solubility of the silver halide precipitates | Add dilute ammonia solution to each PPT and see if it dissolves If not, add conc ammonia solution and see if it dissolves |
What is silver chlorides solubility in ammonia | Soluble in dilute NH3 |
What is silver bromides solubility in ammonia | Insoluble in dilute NH3 Soluble in conc NH3 |
What is silver iodides solubility in ammonia | Insoluble in dilute and conc NH3 |
What is the trend in solubility in ammonia solution from silver chloride to silver iodide | Decreasing soluble |
What does the use of ammonia solution help to distinguish between | Silver halide precipitates when the difference between their colours is not easy to identify |
Disproportionation | A redox reaction in which the same element is both oxidised and reduced |
Equation for the reaction of chlorine with water | Cl2 + H20 > HCl + HClO (Reversible) |
Where is an equilibrium established between in the reaction between chlorine and water | The chlorine, water, hydrochloric acid and chloric (I) acid |
What is chlorine in the reaction between the reaction of chlorine and water | Both oxidised and reduced |
How can chlorine be detected | Very pale green colour |
How can hydrochloric acid be detected | Turns universal indicator paper red |
How can chloric (I) acid be detected | Universal indicator paper red then bleached white |
What happens to the chloric acid that is formed from the reaction between chlorine and water | Decomposes to hydrochloric acid and oxygen |
Equation for decomposition of chloric (I) acid | 2HClO > 2HCl + O2 |
What is the reaction between chlorine and water accelerated by | Sunlight and certain catalysts |
Why is the reaction between chlorine and water accelerated by sunlight | Breaks bonds so lowers activation energy |
What is produced when chlorine reacts with water in the presence of sunlight | Hydrochloric acid and oxygen |
What is the benefit of using chlorine in water treatment | It kills bacteria |
What is the risk in using chlorine in water treatment | It's toxic | Chlorinated hydrocarbons are carcinogenic |
What does the reaction of chlorine with cold dilute sodium hydroxide solution produce | Sodium chloride, sodium chlorate (I) and water |
Equation for reaction between chlorine and sodium hydroxide solution | Cl2 + NaOH > NaCl + NaClO + H2O |
What happens to the colour and smell of the chlorine during the reaction between it and NaOH solution | The green colour fades and the smell is less pungent |
Why is the reaction between chlorine and sodium chloride a disproportionation reaction | Chlorine is both oxidised and reduced |
Main use of sodium chlorate | Domestic bleach |