SC25 Flashcards
(22 cards)
what is a flame test
a test used to identify metal ions present in an ionic compound
What are some properties metal loop used in flame loop require
- shoild be inert(unreactive)
- should not give a colour to the flame
- should have a high melting point
Name two metals used for metal loop
Platinum and Nichrome
Platinum is expensive while nichrome gives a faint orange colour to the flame but is relativelt cheaper
Steps for flametest
- Dip a nichrome loop in concentrated hydrochloric acid, and hold in the flame. repeat this step until the flame soes not give any colour. this step removes remaining salt from previous tests and cleans the loop
2.add a few drops of concentrated hydrochloric acid to the test sample and mske it into a paste
- using the nichrome loop pick up a small amount of the sample paste and hold the loop in the blue part of the flame(roaring flame)
4) observe flame colour
describe the flame colour in differsnt metal ions
lithium, Li+ has red flame colour
sodium,Na+ has yellow
potassium, K+ has lilac
calcium, Ca2+ has orange red
copper, Cu2+ has blue green
strength and weakness of flame test
Pro:
Simple to carry out
do not need expensive equipment
Cons
Large amounts of sample needed
cannot identify different metal ions in a mixture
cannot determine concentration of metal ions in a sample
how does a flame photometer work
measures the light intensity of the flame colour produced by metal ions.
pros and cons of flame photometer
pro
more sensitive
small amounts of sample needed
can identify different metal ions in a mixture
can accurately determine the concentration of metal ions in a sample
cons
more complex to carry out
equipment is expensive
Describe the test for Cations(Positive charged ions)
Uses precipitation tests
-add a few drops of sodium hydroxide into solution
-if certain ions are present a precipitate forms because most hydroxides are insoluble
-different ions give different coloured precipitates
Descibe different colours produced vy cations
Aluminium, Al3+ gives white precpitate
calcium, Ca2+ gives white precipitate
copper,Cu2+ gives pale blue precipitate
iron(II) Fe2+ gives green preciptate
iron(III) Fe3+ gives brown precipitate
give ionic equation of
Copper(II) when sodium hydroxide is present
Cu2+(aq) + 2OH-(aq) > CuOH2(s)
test to distinguish calcium and aluminium ions since both form white precipitate
add a few more drops of NaOH(aq) to the sample
Observstion: White precipitate forms
Conclusion: either Al3+ or Ca2+ ions is present
Confirmatory test
add excess NaOH to the white precipitate formed
Observation and conclusion: if white precipitate dissolves then Al3+ ions are present, if white precipitate remains then Ca2+ ions are presenta
Describe test for ammonium ions (N(H4)+)
1.add sodium hydroxide to test sample
2. gently heat or warm the mixture over a bunsen burner
Observation: sharp smelling gas
Test for NH3 gas:
- hold a damp red litmus paper in the gas produced, if litmus paper turns blue then NH3 is present confirming that the sample contains ammonium
Confirmatory test for ammonium gas
hold a glass rod dipped in concentrated hydrochloric acid near the moith od the test tube where the gas is formed.
observation: a ahite smoke of ammonium chloride forms
What can be used to detect CO2
by limewater test, a precipitation reaction, in presence of carbon dioxide limewater turns cloudy
describe test for carbonate ions
- add dilute nitric acid to the test tube, containing the test sample
observation: bubbles form if co2 is produced - pass the gas through freshly prepared clear limewater
observation; limewater turns cloudy if co2 is present
conclusion; the test sample contains carbonate(CO3)2- ions
Rule for sulphate ions
-most sulphates are soluble except PbSO4, BaSO4, and CaSO4
- Most carbonates are insoluble excspt group 1 carbonates and (NH4)2CO3
Test for sulphate ions
- Add dilute nitric acid (HNO3) to the test sample to rule out the presence of Carbonate ions
- Add barium nitrate solution
observation: white precipitation
conclusion: sulfate(SO4)2- ions is present
rule for halide ions
halides are Cl-, Br-, I-
-All chlorides, bromides, iodides arensoluble except PBCL2, PbBr2, PbI2, AgCl, AgBr, AgI
-Most carbonates are insoluble except group 1
test for halides, chloride, bromide, iodide
1) add dilute nitric acid to an aqeous solution to the test sample in a test tube, to rule out presence of carbonate ions
2) add silver nitrate
after the test of halide describe thenobservation and conclusion to be made
white precipitate of AgCl forms if Cl- ions are present
cream precipitate of AgBr forms if Br- ions are present
yellow precipitate of AgI forms if I- ions are present
notes, why in test of sulfate ions we cannot use sulfuric acid
and why in test for halide we cannot use hydrochloric acid
in test for sulfate ions we cannot use sulfuric acid because it contains sulfate iond which would give a false positive result
in the test for halide ions we cannot use hydrochloric acid, HCl because it contains chloride ions which would give a false positive result
notes, why in test of sulfate ions we cannot use sulfuric acid
and why in test for halide we cannot use hydrochloric acid
in test for sulfate ions we cannot use sulfuric acid because it contains sulfate iond which would give a false positive result
in the test for halide ions we cannot use hydrochloric acid, HCl because it contains chloride ions which would give a false positive result
