topic 9 - separate chemistry 2 Flashcards
why must the test for any ion be unique?
you would never be able to know which specific ion it was if more than one ion gave the same result
what are flame tests used to identify?
metal ions (cations)
describe the method for flame tests
- dip wire (platinum/nichrome) in dilute acid
- hold in blue flame of bunsen flame
- dip loop into solid and place back into blue flame
what colour does lithium (Li+) turn in the flame test?
red
what colour does sodium (Na+) turn in the flame test?
yellow
what colour does potassium (K+) turn in the flame test?
lilac
what colour does calcium (Ca2+) turn in the flame test?
orange-red
what colour does copper (Cu2+) turn in the flame test?
blue-green
why do we use nichrome alloy and platinum wire?
both unreactive (inert) - will not interfere with results
what is a precipitate?
an insoluble solid suspended in a liquid
without using flame tests, how can you test for aqueous metal ions?
add sodium hydroxide (NaOH)
observe colour change
what is the result of a precipitation reaction with aluminium (Al3+) and sodium hydroxide?
white precipitate - adding excess NaOH will dissolve
what is the result of a precipitation reaction with calcium (Ca2+) and sodium hydroxide?
white precipitation
adding excess remains
what is the result of a precipitation reaction with copper (Cu2+) and sodium hydroxide?
blue precipitate
what is the result of a precipitation reaction with iron II (Fe+) and sodium hydroxide?
green precipitate
what is the result of a precipitation reaction with iron III (Fe3+) and sodium hydroxide?
brown precipiate
what is the result of a precipitation reaction with ammonia (NH4+) and sodium hydroxide?
pungent gas produced
forms white smoke of aluminium chloride when hydrogen chloride gas from HCl is held near
what is the test for ammonia?
warm mixture to produce ammonia gas the put damp red litmus paper near it and it will turn blue
what anions do we specifically test for?
carbonate, sulfate, and halides
how do you test for carbonate (CO32-) ions?
add dilute HCl
effervescence could be due to any gas so needs a confirmatory test
gas should be CO2 so can bubble it through like water and see if it turns milky/cloudy
how do you test for sulfate (SO42-) ions?
add dilute HCl and barium chloride (BaCl2)
positive result = white precipitate formed
why do we add dilute HCl when testing for sulfate?
to acidify same and remove any carbonate ions
how do you test for halide ions?
add dilute nitric acid then silver nitrate solution to unknown sample
record colour of ppt. formed
what colour ppt does chloride (Cl-) give?
white
what colour ppt does bromide (Br-) give?
cream
what colour ppt does iodide (I-) give?
yellow
what does instrumental methods of analysis mean and examples?
methods which use machinery
examples: gas chromatography
what are benefits of using instrumental methods of analysis? (3)
accurate, sensitive, speed
what does a flame photometer measure?
light intensity and uses data to determine the concentration of a metal ion in a dilute solution
what is a flame photometer graph called?
a calibration curve
how does a flame photometer work?
sample put into flame and light given off is passed through. output is put on a line spectrum and can be analysed
why is flame photometry good?
can analyse a mixture of ions not just one
