Chapter 8 Flashcards
Reactivity trend down group 2?
Increases down group
Why does the reactivity of group 2 increase down group?
The ionisation energy decreases down the group because the attraction between nucleus and valence electrons decrease as a result of increasing atomic radius and shielding. This makes it easier to remove an electron down the group
Solubility of hydroxides in group 2?
Increases down rhe group resulting in more OH- ions and are more alkaline
Trends of hydroxides in group 2?
pH increases
Alkalinity increases
Solubility increases
Uses of group 2 compounds in agriculture?
Ca(OH)2 is used to increase pH of acidic soils
It neutralises acid to form neutral water
Treating acid digestion
Mg(OH)2 and CaCO3 are used in indigestion tablets
Trends down halogen group?
More electrons
Stronger London forces
More energy required to break IMF
Boiling point increases
Reactivity decreases
Atomic radius increases
Shielding increases
nuclear attraction decreases
What is disproportionation?
Redox reaction which same element is both oxidised and reduced.
Example is chlorine with water and with cold dilute sodium hydroxide
Benefits and risks of chlorine
Kills bacteria in water and ensures water can be drinkable
Chlorine is a respiratory irritant in small concentrations and large concentrations can be fatal
It can react with organic hydrocarbons like methane. This forms chlorinated hydrocarbons which are suspected of causing cancer
However the benefits outweigh the risks as it prevents cholera and typhoid outbreaks
Test for halide ions
Aqueous halide ion + aqueous silver ion —> precipitate of silver halide
1) add AgNO3 to aqueous solution of halide
2) silver halide precipitates have different colours - chloride is white, bromide is cream and iodide is yellow
3) add aqueous ammonia to test solubility of precipitate as it is hard to differentiate the colours of the three halide precipitates
2Cl- + Br2 —>
No reaction
2Cl- + I2 —>
No reaction
2Br- + Cl2 —>
Orange colour from Br2 formation
Cl2 + 2Br- —> 2Cl- + Br2
2Br- + I2 —>
No reaction
2I- + Cl2 —>
Violet colour from I2 formation
Cl2 + 2I- —> 2Cl- + I2
2I- + Br2 —>
Violet colour from I2 formation
Br2 + 2I- —> 2Br- + I2
Between reactions of chlorine, bromine and iodine, what can be concluded?
Chlorine had reacted with both bromine and iodine
Bromine had only reacted with iodine
Iodine has not reacted at all
Carbonate test?
1) add dilute nitric acid to solid or solution in a test tube
2) if bubbles are seen, it could be a carbonate
3) to probe gas is CO2 , bubble gas through lime water.
4) CO2 forms a fine white precipitate of calcium carbonate which turns the lime water cloudy
Carbonate test equation
Na2CO3 (aq) + 2HNO3 (aq) —> 2NaNO3 (aq) + CO2 (g) + H2O (I)
Equation to prove gas is CO2
CO2 (g) + Ca(OH)2 (aq) —> CaCO3 (s) + H2O (I)
Sulfate test?
Barium sulfate is insoluble
Aqueous barium ions + solution of unknown compound
Ionic Equation for sulfate test?
Ba2+ (aq) + SO42- (aq) —> BaSO4 (s)
How would the Ba2+ ions be put into the reaction as?
Aqueous barium chloride or barium nitrate
If u intend to do a halide test after sulfate test, which barium compound should u use?
Barium nitrate as barium chloride introduces chloride ions which can disrupt the experiment
Sequence of tests?
Carbonate, then sulfate then halide test
Why should there be a sequence/correct order of tests?
Carbonate test should be done first as neither sulfate or halide ions can produce bubbles with nitric acid. Carbonate tests can be done without the possibility of an incorrect conclusion
Barium carbonate is also white and insoluble in water so if u carry a sulfate test on a carbonate, it will also give a white precipitate. This is why it is important to carry out carbonate test before sulfate test to ensure there is no carbonate present.
Silver carbonate and silver sulfate are both insoluble in water and will form precipitates in the test, so it is important to carry halide test last to ensure no carbonates or sulfates disrupt the test
How to analyse mixture of ions?
Carry out same tests in correct order on the same solution
Tests for cations?
When heated, aqueous ammonium ions and aqueous hydroxide ions to form ammonia gas
1) NaOH is added to a solution of an ammonium ion
2) ammonia gas is produced, gas wouldn’t be seen as ammonia is soluble in water
3) u can smell the ammonia but moist pH indicator paper can be used. Ammonia is alkaline and it should turn blue.
When group 2 metals react, they lose two electrons and act as…
Reducing agents
