Chapter 8 - Reactivity Trends Flashcards
Describe the trends in group 2 down the group
- increase in atomic radii
- decrease in first ionisation energies
- Be has the highest melting/boiling point. Then generally increases down the group
What are the group 2?
- alkaline earth metals
- metals/react with water to make alkaline solution/ reactive so not found in native form
- REDUCING AGENT - reduces another species
Complete the sentence:
Reactivity…………… Down the group as the ionisation energy… …………. down the group. As well the solubility…………… down the group.
- increase
- decrease
- increase
Describe the trends in boiling point of the halogens down the group
- more electrons
- stronger London forces
- more energy required to break intermolecular force
- boiling point increases
What happens during the halogen-halide Displacement reaction?
- shows that reaction decreases down the group
- chlorine has clearly reacted with Br^- and I^-
- bromide has reacted with only I^-
- iodine has not reacted at all
Describe fluorine
pale, yellow gas reacting with any substance
Describe astatine
Extremely rare as radioactive, decays rapidly, never been seen
Describe the trends in reactivity of the halogens
- atomic radius increase
- more inner shells so shielding increase
- less nuclear attraction to catch an election from another species
- reactivity decrease
Describe the reaction of water and chlorine
•Used in water purification •chlorine is added to water where a disproportional reaction takes place
What are the benefits of Chlorine use?
- Water purification- kills bacteria
* if not used water would be compromised and disease breakout causing mass illness
What are the risks of chlorine use?
- Toxic gas - respirational irritated can be fatal
* Chlorinated hydrocarbon suspected to cause cancer
What does disproportionation mean?
A redox reaction in which the same element is both oxidised and reduced
What is the sequence of tests to find an organic compound?
- carbonate
- sulfate
- halides
What do you do there is a mixture of ions?
You carry out the same tests but with the same solution. What this does it removes step-by-step the different organic compounds
Define what reducing agent means
A reagent that reduces ( adds electron to) another species
Define oxidising agent
A reagent the oxidise (takes electrons from) another species
Halogen-halide displacement reaction: •Cl2(aq)+ Cl^-(aq) -> •Cl2 (aq) + 2Br^-(aq) -> •Cl2 (aq) + 2I^-(aq) -> •Br2 (aq) + 2Cl^-(aq) -> •Br2 (aq) + 2Br^- (aq) -> •Br2 (aq) + 2I^-(aq) -> •iodine ......... react with any of these ions
- no reaction
- 2Cl^- (aq) + Br2(aq) turns orange
- 2Cl^- (aq) + I2 (aq) turns violet
- no reaction
- no reaction
- 2Br^- + I2 (aq) turn violet
- doesn’t
The three reaction in the displacement reaction: Solution in water (colour): •Cl2 = •Br2 = •I2 = solution in cyclohexane (colour): •Cl2 = •Br2 = •I2 =
- pale green
- orange
- brown
- pale green
- orange
- violet
What are the three tests for anions?
- Carbonate test (gases)
- Sulfate test (precipitates)
- Halide test (precipitates)
Describe the carbonate test
Carbonates react with acid to form carbon dioxide gas
1) add dilute nitric acid to solid or solution
2) if you see bubbles, the compound could be a carbonate
3) to prove that gas is carbon dioxide get the bubbles to go through limewater. A white precipitative of calcium carbonate should form if carbon dioxide is present
Describe the sulfate test
You use barium as if a sulfate is present a barium sulfate should form as it is very insoluble in water. A white precipitate should form.
Describe the halide test
They are very soluble in water but silver halides are insoluble. Aqueous silver ions react with aqueous halide ions to form precipitates of silver halides
1) add an silver nitrate to an aqueous solution of a halide
2)silver halide precipitates are different colours • Silver chloride is white • Silver bromide is cream-coloured • Silver iodide is yellow
3) add aqueous ammonia to test solubility
•Chloride is soluble in dilute ammonia • bromide is soluble in concentrated ammonia • iodide is insoluble in concentrated ammonia
What is the test used for cations?
•test for ammonium ions
Describe the test for ammonium ions
When heated together, aqueous ammonium ions and aqueous hydroxide ions react from ammonia gas.
1) Aqueous sodium hydroxide is added to a solution of ammonia ions. Gently warm.
2) ammonia gas is produced. You may be able to smell it. Test with pH indicator paper, it should turn blue
Why are group 2 elements called reducing agents?
In a redox reaction, they lose electrons (oxidation) which is donated to the other reactant, reducing it
What chemical is added to the solution during a displacement reaction and why?
Cyclohexane - the non-polar halogens dissolve more readily with this than water and so the colour change is clearer to see
What colour can be observed when bromide ions are added to chlorine?
Orange - Br2 is formed
What colour can be observed when iodide ions are added to chlorine?
Violet - I2 is formed
What colour can be observed when chloride ions are added to bromine?
No reaction
What is a disproportionation reaction?
A chemical reaction in which an element is both oxidised and reduced
