CH. 8 reactivity trends
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what happens to the reactivity of elements going down group 2 and why
increases, due to the decrease of ionisation energy going down due to increasing atomic radius and shielding so less nuclear attraction
group 2 metal oxide + water =
OH- and metal ions, and some metal hydroxides
explain the trend in solubility in group 2 metal hydroxides going down the group
solubility increases, resulting in an increase in OH- conc so an increase in PH and alkalinity
group 2 hydroxides, carbonates, and oxides are all what
bases
group 2 compound use in agriculture
Ca(OH)2 (lime) is added to acidic soil to increase the PH.
group 2 compound use in medicine
Mg and Ca carbonates treats acid indigestion
what happens to the boiling point of halogens going down the group
increases, due to more electrons so stronger London forces needing more energy to break
what happens to the reactivity of halogens going down the group
decrease, due to increase in atomic radius and shielding so less nuclear attraction to capture an electron from another species
colour of halogen solutions in water and what can u do to be able to tell them apart even more
Cl2 - pale green Br2 - orange I2 - brown u can add a non polar solvent like cyclohexane and shake. Cl2 - pale green Br2 - orange I2 - violet
disproportionation
a redox reaction in which the same element is both oxidised and reduced
using chlorine to purify water
disproportionation reaction Cl2(aq) + H2O(l) —> HClO(aq) + HCl(aq) bacteria is killed by the chloric(1) acid (a weak bleach) and chlorate(1) ions ClO-
chlorine with cold dilute aqueous NaOH
disproportionation chlorine isn’t very soluble in water, the presence of NaOH means much more Cl dissolves Cl2(aq) + 2NaOH(aq) —> NaCLO(aq) + NaCl(aq) + H2O(l) large conc of chlorate(1) ClO- ions from the NaClO formed this solution is used as a household bleach
benefits and risks in use of chlorine in treatment of water
it kills bacteria and makes sure water is fit to drink but chlorine gas is a respiratory irritant and possibly fatal. it can also react with organic hydrocarbons like methane formed from decaying vegetation forming chlorinated hydrocarbons which are suspect of causing cancer risk of negatives is far outweighed by the positives of not getting cholera or typhoid
how do u test for halide ions
they react with aqueous silver ions forming silver halide precipitates mix aqueous silver nitrate to the aqueous solution of suspected halide Cl- forms white precipitate, soluble in dilute NH3 Br- forms a cream precipitate, soluble in conc NH3 I- forms yellow precipitate, insoluble in NH3
carbonate test
react with nitric acid HNO3. should bubble through lime water will turn cloudy if CO2 is present
sulfate test
add aqueous barium ions in the form of barium chloride or nitrate (nitrate if a halide test is to follow). if the solution contains sulfate ions a white precipitate will form
when testing for halides sulfates and carbonates what is the correct order to test in
• carbonate • sulfate (barium carbonate could give a false + so test for carbonate first) • halide (sliver carbonate and sulfate are insoluble precipitates could skew results so test for carbonates and sulfates first)
ammonium test NH4+
heat solution with aqueous NaOH if ammonium present ammonia will form and be released as a gas it will turn moist PH indicator blue solution must be heated to release ammonia gas as it is soluble in water