Chapter 8 - Reactivity Trends Flashcards
What are group 2
Alkaline Earth Metals
Trends in reactivity group 2 - state
They become more reactive down the group.
Trends in reactivity group 2 - explain
Their 1st and 2nd ionisation energies reduce down the group. Because as you go down the group, the attraction between the nucleus and the outer electrons decreases. This makes it easier to lose those electrons.
Trends in solubility of metal hydroxides - state and explain
Increases down the group.
As solutions become more alkaline
Experiment to show the trend of solubility in metal hydroxides
- Add a spatula of group 2 hydroxide to a text tube with water
- Shake
- Eventually, a mixture of a saturated solution should be made, with some white solid undissolved at the bottom.
- Measure the pH.
Uses of group 2 elements in agriculture
Added as lime to fields to neutralise the acids and give products of water.
Uses of group 2 elements in medicine
Antacids to treat acid indigestion.
CaCo3 or Mg(OH)2 are used.
Sodium and water
Rapid reaction
It floats and curls up into a ball and floats on the surface of the water due to the hydrogen being formed.
Very exothermic reaction. Hydrogen is formed due to a single displacement reaction.
Tested by doing a squeaky pop test.
Squeaky pop test
A test tube of hydrogen is used to blow out a flame with a “squeaky pop” sound.
Magnesium and water
Ionisation energy increases (from sodium) Reactivity decreases More dense that water so it sinks There's no apparent reaction Very slow reaction without heat
Magnesium and steam
Use a cotton wool with water.
Changes to MgO, which is a white powder.
Magnesium and oxygen
Lightly exothermic
Very bright flame produced.
Sulfur and oxygen
Burns bright blue flame
SO2 is a choking gas.
Sulfur and water
Insoluble in water.
Sodium and steam
Extremely exothermic
What group is the most reactive non-metallic group
Group 7 - Halogens
F2 state
yellow gas
Cl2 state
Green gas
Br2 state
Brown liquid
I2 state
Grey-black solid
At2 state
Never seen
Trend in boiling point for group 7 - explain
As you go down the group, there are more electrons
So stronger London forces
So more energy to break the bonds
Hence boiling point increases.
Halogen and halide reactions
Displacement reactions
How to carry out a halogen- halide reaction?
Mix a solution of the halogen with aqueous solutions of the other halides.
In Halogen and halide reactions , when can a reaction take place?
Only when the halogen is more reactive that the halides present.
How can you differentiate between bromine and iodine
They have similar colours so
Add some organic non-polar solvent like a cyclohexane
The halogens will dissolve more readily.
Iodine becomes a deep violet and bromine a yellow-orange.
What is a disproportionation reaction
A redox reaction where oxidation and reduction happen to the same element.
Benefits of chlorine
Kills bacteria
Cl2 is a toxic gas.
What is qualitative analysis
It relies on simple observations, rather than measurements.
Observations such as gas bubbles etc.
Test for anions include:
Carbonates
Sulfates
Halides
Carbonates test
In a test tube, add dilute nitric acid to the solution
If there are bubbles formed, then it is likely carbon dioxide.
Then bubble the gas through limewater. If it turns cloudy, then the gas formed was carbon dioxide.
Sulfate test
Add aqueous barium chloride (or nitrate).
If a dense white precipitate is formed, and it sinks to the bottom, then it is a sulfate.
Ba (2+) + SO4 (-2) –> BaSO4
Halides test
Most halides are soluble, except Ag. ions.
Add aqueous silver nitrate to the solution.
Silver halide becomes:
- White - chloride
- Cream - bromide
- Yellow - iodide
Halides- How to determine the colours
Add some aqueous ammonia, as it turns the precipitate soluble
Sequences for the anions
- Carbonate
- Sulfate
- Halide
Sequence for a mixture or ions
Carry out the tests in the same sequence and on the same solution.
Test for cations
- Add ammonium ions (NH4+)
- Add NaOH solution
- Ammonia gas is made. no bubbles
- Warm and ammonia gas is released.
- Test using moist pH indicator paper which should turn blue.
What is the colour of the halides dissolved in water?
Cl2 - pale green
Br2 - orange
I2 - brown
What is the colour of the halides dissolved in cyclohexane (the top layer)?
Cl2 - pale green
Br2 - Orange
I2 - purple/ violet.
Cl2 + H20
HClO + HCl
Cl2 + 2NaOH
NaClO + NaCl
Why are there 2 different layers when the cyclohexane is mixed with the halide (mixed in water)
Because the water is more dense than the cyclohexane and the halide mixture. So the other mixture gathers on the top layer.
Why is ammonia used?
Generally just to differentiate between AgI, AgBr, and AgCl precipitates.
Why is the cyclohexane used?
To differentiate between the different Halides ions.
Group 2 Hydroxides solubility in water
Increases as you go down the group. Hence, more OH- ions are produced and the solution becomes more alkaline.
Group 2 Oxides solubility in water
Increases as you go down the group.
Why do we use Acidified AgNo3 for the testing of Halide ions?
To find out if there are any carbonate ions because the carbonate ions can react with the Silver ions to produce a white precipitate.
Why should you use Dilute nitric acid rather than sulphuric acid in the test for carbonate?
Because when sulphuric acids reacts, it produces Sulphate ions, which can be detected later on in the sulphate test.
Cl2 + NaOH (hot and concentrated)
Cl2 + 6NaOH -> NaClO3 + 5NaCl + 3H20
AgF + NH3
Soluble in water so it doesn’t form a precipitate.
AgCl + NH3
Dissolves in dilute Ammonia solution
AgBr + NH3
Dissolves in concentrated ammonia solution.
AgI + NH3
Doesn’t dissolve at all
