Starting with oxidation and reduction & group 2 elements
What is a redox reaction?
A reaction in which electrons are transferred.
Reduction and oxidation happen simultaneously.
What is an oxidising agent and a reducing agent?
Oxidising agent - accepts electrons and get reduced.
Reducing agent - donates electrons and get oxidised.
An increase in "positiveness" due to loss of electrons.
Addition of oxygen or removal of hydrogen.
Decrease in "positiveness" due to gain of electrons.
Removal of oxygen or addition of hydrogen.
One element can be both oxidised and reduced in the same reaction. What is this reaction called?
A disproportionation reaction.
What is the usual oxidation number of oxygen? What are exceptions?
Exception - in peroxides (H2O2) = -1
and when it combines with fluorine = positive
What is the usual oxidation number of hydrogen? Exceptions?
Exception - in metal hydrides = -1
What is the usual oxidation number of chlorine? Exceptions?
Exception - with oxygen & fluorine = positive
What is usual oxidation number of bromine (Br)? Exceptions?
Exception - with O, F, Cl = positive
What is the usual oxidation number of iodine? Exceptions?
Exception - when combined with O, F, Cl, Br = positive
Oxidation number of fluorine? Exceptions?
(First) ionisation energy becomes what as you go down Group 2? Why?
Ionisation energy decreases down the group (so easier to ionise)
More electron shielding from inner shells/ energy levels.
More distance from the positive nucleus. (Positive charge of nucleus does increase, but nuclear charge effect overridden)
Describe the reaction of Group 2 elements with water.
Gives metal hydroxide and hydrogen (gas) [for calcium, strontium & barium]
Increase in reactivity down the group. (Be doesn't react, Mg very slowly, Ba rapidly - with COLD water)
[Mg reacts rapidly with steam to form magnisium oxide (MgO) and hydrogen.]
Describe the reaction of Group 2 elements with oxygen.
Form solid white oxides.
Magnesium element burn with brilliant white flame, and other burn with their characteristic flame colours.
What is formed when a Group 2 element reacts with chlorine?
Solid white chloride formed.
What does the reaction of Group 2 oxides with water form?
Metal hydroxides, which dissolve to produce alkali solution.
Oxides form more strongly alkaline solutions down the group, because the hydroxides get more soluble.
(BeO doesn't react though)
What do Group 2 metal oxides form when reacting with dilute acid?
They neutralise it, and therefore form a salt (eg. MgCl2, or Ca(NO3)2 ) and water.
What is formed when Group 2 hydroxides react with dilute acid?
Salt and water produced.
Describe the solubility of Group 2 hydroxides and Group 2 sulphates. What is the general pattern?
Solubility increases down group for hydroxide.
Solubility decreases down group for sulfate.
Generally, Group 2 compounds that contain singly charged negative ions (eg OH-) increase in solubility down the group, and those containing doubly charged negative ions (eg SO42-, CO32-) decrease in solubility down group.
(Barium sulfate is insoluble)
Roughly, what is thermal decomposition and thermal stability?
Thermal decomposition is when a substance breaks down (decomposes) when heated.
The more thermally stable a substance is, the more heat it will take to break it down.
Thermal stability of Group 1&2 carbonates and nitrates ______ down the group. Why?
Carbonate and nitrate anions are large, and can be made unstable by presence of cation. Cation polarises anion, distorting it.
The greater the distortion, the less stable the anion.
Smaller cations (have higher charge density) and distorts anions more.
THUS, as ionic radius increases down the group, the more distorted anions are going to be at the top, and therefore more thermally stable down the group.
Group2 carbonates and nitrates are ____ stable than those of Group 1. Why?
Group2 c&n are less stable than those of G1.
Because G2 cations have 2+ charge, whereas G1 have 1+, therefore G2 cations distort the anion more, and thus less thermally stable.
Group 2 carbonates decompose to form what?
the Oxide and Carbon dioxide
(MgCO3 ------ MgO + CO2)
Group 2 nitrates decompose to form what?
The oxide, nitrogen dioxide and oxygen.
eg. Ca(NO3)2 (s) ---- 2 CaO (s) + 4NO2(g) + O2(g)
Group 1 nitrates decompose to form what?
The nitrite and oxygen.eg. 2KNO3(s) ----- 2KNO2(s) + O2 (g)
(Except Lithium nitrate which decomposes to form Li2O, NO2 and O2)
Give 2 ways of testing thermal stability of nitrates.
How long it takes until oxygen is produced (ie. to relight a glowing splint) OR
How long it takes until a brown gas (NO2) is produced. [This needs to be done in fume cupboard as nitrogen dioxide is toxic]
Give a way to test the thermal stability of carbonates.
Measure how long it takes for carbon dioxide to be produced. (Bubble through limewater which turns cloudy with carbon dioxide).