C7, 9, 10 Flashcards
reduction
gain of electrons
loss of oxygen
gain of hydrogen
oxidation
loss of electrons
gain of oxygen
loss of hydrogen
reducing agent
electron donor
oxidising agent
electron acceptor
oxidation state rules
uncombined elements os = 0
oxidised = positive os
reduced = negative os
molecular ions- sum of os = charge on ion
in a compound, the most electronegative has the -ve oxidation state
element + os state in compound
Hydrogen- +1 except in metal hydrides
group 1- always +1
group 2- always +2
Aluminium- always +3
Oxygen- -2 except peroxides (-1) and OF2 (+2)
Fluorine- -1
Chlorine- -1 except in compounds with F and O- positive values
balancing redox equations
- os state above each element
- identify species o/r
- balance the no of e- transferred for each equation
- include in unbalanced equation
- balance remaining atoms
when working out half equations, may need to include spectator ions to balance charges
redox reactions in certain conditions: acidic, basic, aqueous
acidic: H+ LHS, product water
basic: OH- LHS, product water
aqueous: H2O LHS H+ or OH- product
size of atoms down group 2
atoms get bigger going down group
atomic (metallic) radii increase because each element has an extra main level of electrons
trend in melting points down group 2
in general have high melting points, typical of giant metallic structure
going down group, electrons in sea of delocalised e- are further away from positive nuclei
so strength of metallic bond decreases down group
(Mg doesnt fit trend)
group 2 ionisation energies
amount of energy needed for 1st and 2nd IE needed for complete ionisation
first and second ionisation energies decrease down group
- takes less energy to remove the e- as they become further away from +ve nucleus
- nucleus is more effectively shielded by inner shells of e-
group 2 reactivity - water and steam
in all reactions, get more reactive going down group
reaction with steam
M + H2O –> MgO +H2
reaction with water at 25 degrees
M + 2H2O –> M(OH)2 + H2
metals get more reactive with water going down the group
they are redox reactions
Magnesium Hydroxide use
milk of magnesia
used in indegestion remedies to neutralise excess stomach acid which causes heartburn
reaction of Mg with water/steam
reacts very slowly with cold water
but rapidly with steam, to form an alkaline oxide and hydrogen
reaction of Ca with water/steam
reacts in the same way as Mg but more vigorously, even with cold water
strontium and barium react even more vigorously
Calcium Hydroxide use
slaked lime
treats acidic soil
- most plants have optimum level of acidity/ alkalinity
solubility of group 2 hydroxides
going down group, hydroxides become more soluble
magnesium hydroxide is almost insoluble
barium hydroxide dissolves to produce a strongly alkaline solution
solubility of group 2 sulfates
going down group, sulfates become less soluble
barium sulfate = virtually insoluble
use of BaSO4
taken as a barium meal to outline gut in x-rays
heavy Ba metal good at absorbing x-rays
test for sulfate ions
uses the insolubility of BaSO4
- solution acidified with nitric/ hydrochloric acid
- BaSO4 added
- positive = white ppt
why are solutions under test first acidified
to remove any carbonate ions as CO2
extraction of titanium
- titanium properties and uses
titanium = strong, low density, high melting point
used in aesorpace industry and for making replacement hip joints
most metals are found in the earth as oxides and metal = extracted by reacting with carbon
metal oxide + carbon –> metal + carbon dioxide
this method cannot be used for titanium because titanium reacts with carbon to form titanium carbide TiC, which makes the metal brittle
- so the titanium oxide is first reacted with chlorine and carbon to form titanium chloride and carbon monoxide
- the TiCl4 is then reduced to titanium by reaction with Magnesium
TiCl4 (l) + 2Mg(s) –> 2MgCl2 (s) + Ti
