the halogens and qualitative analysis Flashcards
describe the colours and states of the halogens
fluorine- pale yellow gas
chlorine- pale green gas
bromine-brown/orange liquid
iodine- grey solid
what group is the halogens
group 7
what is the trend in boiling points down the halogens
increases
London forces increase due to increase in size and relative mass of
what is the trend in electronegativity as we go down the halogen group
decreases
atoms get larger and distance between positive nucleus and bonding electrons increase, also more shielding
more reactive halogens will ______ less reactive halide ions
displace
halogens are _____ oxidising as we go down the group
less
what is the trend in reactivity as you go down the group
decreases
atoms with a smaller radius attract electrons better than larger atoms
draw a displacement table
how would you test for halides and what would be the result
add silver nitrate
Chloride ions form white precipitate
bromide ions form cream precipitate
iodide ions form yellow precipitate
add ammonia
white dissolves in dilute NH3
cream dissolves in conc. NH3
yellow does not dissolve
describe how bleach is made and what his its chemical name
disproportionation reaction
2NaOH + Cl—- NaClO + NaCl + H2O
chlorine is reduced and oxidised
sodium chlorate
describe how water is sterilised
chlorine used to kill bacteria
produces chlorate ions (clO-)
H2O+Cl—— HCl + HClO
chlorine is oxidised and reduced which is a disproportionation reaction
chloric acid ionises to make chlorate ions
HClO + H2O—– ClO- + H3O+
what are the advantages and disadvantages of chlorinating water
ad- destroys microorganisms, long lasting
reduces growth of algae which discolours water and makes it taste bad
dis- cl gas is toxic and irritates respiratory system, liquid chlorine can cause chemical burns, can react with organic compounds to form chloroalkanes which can cause cancer
what alternatives are there to chlorination of water and what are the positives and negatives for each one
- ozone- powerful oxidising agent but has shot half life so not permanent, expensive to produce
- UV light- damages DNA in microorganisms, ineffective in cloudy water
how do you test for ammonium compounds
add NaOH, gently heat, ammonia produced if present, will turn damp red litmus paper blue
how do you test for hydroxides
turn red litmus paper blue
