✨Module 3: Reactivity trends Flashcards
Write an oxidation reaction with a group 2 metal.
Ca = Ca2+ + 2e-
Ca is oxidised. The group 2 element is called the reducing agent as it has reduced another species.
Group 2 metals react with water to form …
Metal hydroxide and hydrogen gas.
Describe some uses of group 2 compounds.
Ca(OH)2 is used in agriculture to neutralise the acid in soils, forming neutral water.
Mg(OH)2 and CaCO3 is used to treat acid indigestion by neutralising HCL in stomach.
Mg(OH)2 is …
Slightly soluble in water so fewer free
OH- ions are produced so lower pH.
What happens to halogens in a redox reaction? Give an equation to show this.
Each halogen atom is reduced, gaining 1 electron to form 1- halide ion.
Cl2 (g) + 2e- = 2Cl-
Another species loses electrons to halogen atoms - it is oxidised.
Why do halogens undergo redox reactions?
They have the outer shell s2p5 electron configuration. They will react by gaining one electron in redox reactions to form 1– ions.
Reactivity of halogens decrease …
Down the group, as the atoms get bigger with more shielding so they less
easily attract and accept electrons. They therefore form -1 ions less easily.
Explain the halogen-halide displacement reactions.
Chlorine displaces bromide, bromine displaces iodide. Iodine doesn’t react at all. All are aqueous state symbols when writing equations.
What are the colours of halogen solutions in water?
What about in an organic non-polar solvent such as cyclohexane? (Use this when it’s difficult to differentiate between bromine and iodine solution).
Chlorine - very pale green solution.
Bromine - orange solution.
Iodine - brown solution.
Chlorine - pale green/colourless.
Bromine - orange solution.
Iodine - purple solution.
Fluorine is a …
Pale yellow gas that is toxic.
Benefits and risks of chlorine use?
Disinfects water.
Toxic gas that acts as a respiratory irritant.
The benefits to health of water treatment by chlorine by its killing of bacteria outweigh its risks of toxic effects from formation of chlorinated hydrocarbons.
Test for carbonate ions?
- In a test tube, add dilute nitric acid to substance being tested and observe effervescence.
- Bubble gas through limewater to test for CO2 – will turn limewater cloudy.
Test for sulfate ions?
Ba2+ (aq) + SO42- (aq) = BaSO4 (s)
BaCl2 solution is added to substance. If doing halide test afterwards, use barium nitrate instead.
White precipitate of barium sulfate forms.
How to test for halides?
Silver halides are insoluble in water, so aqueous silver ions react with aqueous halide ions to form a precipitate of silver halides. Ag+ (aq) + X- (aq) = AgX (s)
1. Add nitric acid (reacts with any carbonates present to prevent formation of the precipitate (Ag2CO3).
2. Aqueous silver nitrate is added drop
wise to aqueous solution of halide.
What are the colours of the precipitates formed in the halide test?
Silver chloride - white precipitate
Silver bromide - cream precipitate
Silver iodide - yellow precipitate
Write an ionic equations for the halide test.
Ag+ (aq) + Br- (aq) = AgBr (s)
What do you do to the halide precipitates to be more accurate with observation?
Add aqueous ammonia to test solubility of precipitate.
Chloride is soluble in dilute NH3 (aq).
Bromide is soluble in concentrated NH3 (aq)
Iodide is insoluble in NH3 (aq)
Test for ammonium NH4+?
- Warm aqueous NaOH is added to solution of ammonium ion.
- Ammonia gas is produced but won’t see gas bubbles as ammonia is soluble in water.
NH4+ (aq) + OH- (aq) = NH3 (g) + H2O (l) - Mixture is warmed and ammonia gas is released. Ammonia will turn moist indicator paper blue.
Barium carbonate is a …
Precipitate
