Reactivity Trends A1 Flashcards
Module 3
What kind of agents are group 2 elements? Why?
Reducing agents. They lose electrons (are oxidised) causing other elements to be reduced.
Properties of Group 2 elements:
Similar to metals:
- high m.p and b.p.
- good thermal and electrical conductors
What happens to reactivity as you go down group 2? Why?
Reactivity increases
1) increased atomic radius
2) increased electron shielding
3) So nuclear attraction to outer electrons is weaker.
Group 2 oxides act as ____ and react with water to form _______ and with acids to form ____.
bases
hydroxides
salts
The solubility of the group 2 hydroxides ______ down the group and as a result, so will ______.
increases
alkalinity
All group 2 carbonates will react with acids. They will also _________ ________ to form an oxide.
e.g.
thermally decompose
e.g. MCO3 + 2HCl –> MCl2 + H2O + CO2
MCO3 –> MO + CO3
Describe the uses of Group 2 compounds - give examples
Calcium Hydroxide used to neutralise acidic soils.
Magnesium hydroxide and calcium carbonate used in antacids (e.g. Rennie’s)
What is disproportionation?
When the same element is both oxidised and reduced in a reaction.
What is the oxidation number of an element in it’s natural state?
0
What is the sum of oxidation numbers in a molecule?
0
What is the normal oxidation number of Oxygen and what are the two exceptions?
-2
Peroxides (e.g. H2O2) where O is -1
and When combined with F it is +2 (e.g. O2F)
What is the exception to the halogen’s oxidation numbers being -1?
When bonded to oxygen or other halogens.
Why is using Chlorine in the process of cleaning water a problem?
It is toxic and it reacts with organic substances to form chloroalkanes which are carcinogenic.
Cl2 + 2NaOH —>
Cl2 + H2O —>
What type of reaction are these?
—> NaClO + NaCl + H2O
—> HClO + HCl
Disproportionation
Remember to explain USING OXIDATION NUMBERS
The b.p. of Halogens ________ as you go down the group. Why?
Increases - more electrons so stronger London forces
The reactivity of Halogens _______ as you go down the group. Why?
Decreases
- atomic radius increases
- more inner shells to shielding increases
- less nuclear attraction to attract electrons
Put the Halogens in order of Oxidising ability (highest to lowest).
F, Cl, Br, I (order of reactivity)
What are the colours of Chlorine, Bromine and Iodine when in aqueous solution and organic solvent?
Aqueous Sol:
Cl = Pale Green
Br = Orange
I = Brown
Organic Solvent:
Cl = Pale Green
Br = Orange
I = Violet
What is the test and positive result for carbonate ions?
React with dilute nitric acid - bubbles/effervescence - turns lime water cloudy
What is the test and positive result for sulfate ions?
add aqueous barium chloride - white precipitate
What is the test and positive results for halide ions?
Add silver nitrate - Cl white ppt, Br cream ppt, I yellow ppt
What is the effect of adding dilute and conc ammonia to silver halide ppts?
AgCl soluble in dilute
AgBr soluble in conc
AgI not soluble
What is the correct sequence of tests for halide, carbonates and sulfates?
Carbonate
Sulfate
Halide
Otherwise false positives may occur
Cats Salivate Happily
What is the test and positive result for ammonium ions?
Add Sodium hydroxide - heat over flame and test fumes with moist indicator paper. Will turn paper blue (alkali)
