Reactivity trends Flashcards
what happens to reactivity down group 2?
reactivity increases
what reactions do group 2 elements undergo? (and products)
redox with:
- oxygen (metal oxide)
- water (metal hydroxide + H2)
- acid (salt + H2)
what happens to ionisation energy down group 2?
IE decreases
what observations would be made when group 2 reacts with water?
- increase in pH (shown by indicator)
- solid precipitate once the solution becomes saturated (group 2 hydroxide are sparingly soluble)
what happens to solubility down group 2 hydroxides? and what effect does this have on pH?
solubility increases which increases [OH-] so increases pH
uses of group 2 compounds
- Ca(OH)2 used in agriculture (as lime) to increase pH of acidic soils (producing water)
- Mg(OH)2 or CaCO3 used in antacids (treating acid indigestion) by neurtalising HCl/stomach acid
what happens to boiling point down group 7?
boiling point increases (more e-, stronger LDFs)
chlorine state and colour (RTP)
pale green gas
bromine state and colour (RTP)
red-brown liquid with orange vapour
iodine state and colour (RTP)
solid grey-black crystals
what reactions do halogens undergo?
- redox
- halogen-halide displacement
what happens in halogen-halide displacement?
more reactive halogen displaces the halide from solution (causes colour change)
reaction and colour change when I-(aq) is mixed with Cl2(aq)
2I- + Cl2 –> I2 + 2Cl-
pale green to violet
colours of Cl2, Br2, I2 in water
Cl2 - pale green
Br2 - orange
I2 - brown
colours of Cl2, Br2, I2 in cyclohexane
Cl2 - pale green
Br2 - orange
I2 - violet
how can you tell apart solutions of iodine and bromine in water?
- add cyclohexane and shake mixture
- halogens will dissolve more readily
- colours will be more obvious
fluorine state and colour
pale yellow gas
disproportionation
redox reaction in which the same element is both oxidised and reduced
two examples of disproportionation
- Cl2 + H2O
- Cl2 + NaOH
how is Cl used in disinfectant and water sterilisation?
chlorate, ClO- ions kill bacteria
how can you demonstrate ClO- acting as bleach?
- mix Cl2 + H2O
- add indicator
- indicator will turn red (HCl and HClO are acidic) then colour will disappear as it is bleached
why would use dissolve NaOH in water before adding Cl2?
- Cl2 is sparingly soluble in water
- more Cl2 dissolves in the presence of NaOH
- Cl2 reacts with NaOH in a disproportionation reaction to form ClO-
risks of chlorine use
- Cl2 reacts with organic hydrocarbons such as methane from decaying vegetation
- this forms chlorinated hydrocarbons which are suspected carcinogens
benefits of chlorine use
- prevent outbreaks of waterborne diseases like typhoid and cholera
