Chapter 8 Reactivity Trends Flashcards
Group 2 metal + water
Metal hydroxide + hydrogen
Why does reactivity increase as you go down Group 2
- Group 2 experience 2 ionisation energies: 1st and 2nd ionisation energies
- The ionisation energies decrease as you go down the group because attraction between the nucleus and outer electrons decreases due to increasing atomic radius and increased shielding
Solubility of Group 2 metal hydroxides in water
Increases as you go down the group -> so the resulting solutions contain more OH- ions
This can be proven by measuring the pH of the solutions
Uses of Group 2 compounds as bases
- Calcium hydroxide is added to fields -> to increase pH of acidic soils
- Magnesium and calcium carbonates are used as antacids in treating acid ingestion
Group 7 - Halogens
- Most reactive non-metallic group
- Occur as stable halide ions dissolved in sea water
Group 7: Trend in boiling points
- Increases as you go down the group
- more electrons
- so stronger london forces
- so more energy needed to overcome these forces
- so boiling point increases
Halogen-halide displacement reactions
If the halogen is more reactive than the halide in the solution, it will displace it
How to tell the difference between iodine and bromine in water (they look very similar orange-brown colour)
Add cyclohexane and shake
- iodine goes deep violet
- bromine stays orange
Colours of the halogens
Fluorine: pale yellow gas
Chlorine: pale green gas
Bromine: red-brown liquid
Iodine: shiny grey-black solid
Group 7: Trend in reactivity
- Atomic radius increases
- More inner shells so shielding increases
- Less nuclear attraction to capture an electron from another species
- Reactivity decreases
Disproportionation
A redox reaction in which the same element is both oxidised and reduced
Examples of disproportionation reactions
Chlorine + water
Chlorine + dilute sodium hydroxide
Chlorine + water
Cl2 + H2O -> HClO + HCl
HClO
chloric acid
Uses of chloric acid
Weak bleach
Chlorine + sodium hydroxide
NaClO + NaCl + H2O
NaClO
Sodium chlorate
Benefits of chlorine
Cleaning water (kills bacteria)
Risks of chlorine
- Toxic gas
- Can react with organic hydrocarbons -> forms chlorinated hydrocarbons which cause cancer
Tests for anions
- Carbonate ions
- Sulfate ions
- Halide ions
Test for carbonate ions
- Add dilute nitric acid
- If bubbles are seen, it is a carbonate
- To test the gas for CO2, bubble through limewater and if it goes cloudy its CO2
Limewater
Calcium hydroxide
Test for sulfates
- Add barium nitrate or barium chloride
- White precipitate of barium sulfate formed if sulfate is present
When to use barium chloride or barium nitrate in sulfate test
If doing a halide test afterwards, use barium nitrate to avoid introducing chloride ions
Test for halides
- Add silver nitrate
Tesy for NH4+
- Add NaOH to a solution containing an ammonium ion
- Ammonia gas is. produced
- Warm and test with moist red litmus paper, it will go blue
