Group 2 And group 7 Flashcards
What is a halide
Group 7 with an ion 1- charge
Eg I-
What do hallides behave as?
Reducing agent
What is a reducing agent?
Electron pair donor
Reducing strength of hallides
Increase down the group
Ionic radius increases
Weaker attraction between outer electron and nucleus
Two ions that can reduce sulphuric acid
Br = SO2
I= SO2 , H2S , S
Write out half equations for both and combine
What is SO2?
Acidic gas
What is H2S?
Bad egg smell
What is S?
Sulphur, which is a yellow solid
Half equation of I- to I
2I- = I2 + 2e-
What does I2 appear as
Black solid
What does BR2 appear as
Brown fumes
Halide test
- Dissolve sample in water.
- AddHNO3 Acid to remove any possible carbonate impurities which would give a false positive and don’t add HCL or sulphuric acid for the step
- Add AgNo3 Solution
Ag+ + Cl- = AgCl = white ppt
Ag+ + Br- = AgBr = cream ppt
Ag+ + I-=AgI= yellow ppt
Ag+ +f- =AgF = colourless solution - Add dilute nitric acid
White precipitate dissolves cream and yellow precipitate insoluble - Add concentrated ammonia to the sample
Cream precipitate dissolves but yellow precipitate insoluble
Equation with NH3 in halide test
AgCl + 2NH3 → Ag(NH3)2+ + Cl−
AgBr + 2NH3 → Ag(NH3)2+ + Br−
What are halogens?
Diatomic molecules
Eh F2
What does a halogen behave as?
Oxidising agent
What is a oxidising agent?
Electron acceptor
Trend in oxidising ability of halogens
Decreases down the group as larger radius so weaker attraction between nucleus and incoming electron
Order of displacement reactions
I2= most powerful
Cl = weakest
Use of chlorine
Added to water to sterilise water by killing bacteria and microorganisms
Why is chlorine added in low concentrations?
Because it is toxic
Reaction between chlorine and water
Cl2 + H2O ⇌ HCl + HClO
What type of reaction is between chlorine and water?
Disproportionation reaction as chlorine is reduced to HCl and chlorine is oxidised to HClLO
Chlorine + Sodium Bromide → Bromine + Sodium Chloride
Cl2 + 2NaBr → Br2 + 2NaCl
Cl2 + 2Br− → 2Cl− + Br2
Chlorine + Sodium Iodide → Iodine + Sodium Chloride
Cl2 + 2NaI → I2 + 2NaCl
Cl2 + 2I− → 2Cl− + I2
Bromine + Sodium Iodide → Iodine + Sodium Bromide
Br2 + 2NaI → I2 + 2NaBr
Br2 + 2I− → 2Br− + I2
Reactivity of group 2 metals down the group
Decreases
Reaction of group 2 metals with liquid water
Mg(s) + 2H2O(l) → Mg(OH)2(aq) + H2(g)
Reaction of group 2 metals with steam
Mg(s) + H2O(g) → MgO(s) + H2(g)
Observation of MgO
White solid produce
Bright light
Use of Mg in Extraction of Ti from TiCl4
TiCl4 + 2Mg 2MgCl2 + Ti
Group 2 hydroxide. Solubility.
Increases down the group
Magnesium hydroxide equation and. Observation.
Mg2+(aq) + OH−(aq) → Mg(OH)2(s)
White ppt
What could you use to test for the presence of Mg2+ ions in a solution?
NaOH
What could you use to test for the presence of OH− ions in a solution?
Mg(NO3)2
Uses of Magnesium Hydroxide:
• Indigestion relief
• Often called ‘milk of magnesia’
Group 2 sulphate solubility
Decreases down the group
Ionic equation of barium sulphate. And observation.
Ba2+(aq) + SO42−(aq) → BaSO4(s)
White ppt
What could you use to test for the presence of Ba2+ ions in a solution?
H2SO4
What could you use to test for the presence of
SO42− ions in a solution
BaCl2
Use of barium sulphate
Taking X-rays of the stomach (Barium meal)
Sodium chloride and fluoride when reducing H2SO4
Both are too weak so form steamy / misty fumes
NaCl + H2SO4 = HCl +NaHSO4
