qualitive analysis Flashcards
whats the test for anions
we test for carbonates
sulfates
and halides
whats the test for the presence of carbonates
carbonates react with acids to form CO2 gas
What’s the equation for carbonate testing
2H+ + CO3^2- ———> CO2 + H2O
what happens in the test of carbonates
if you see bubbles the unkown compound could be a carbonate
What do you do to prove that the gas is CO2
bubble gas through limewater - a saturated aqueous solution of calcium hydroxide Ca(OH)2
Carbon dioxide reacts to form a fine white precipitate of calcium carbonate which turns lime water cloudy
CO2(g) + Ca(OH)2(aq) ——> CaCO3(s) + H2O(l)
What’s the test based on gases for anions
carbonate test
what is the test based on precipitate for anions
sulphate test
what happens in the sulphate test
most sulphates are soluble in water but barium sulfate BaSO4 is very insoluble in water. The formation of a white precipitate of barium sulfate is the basis for the sulfate test, in which barium ions are added to the solution of an unknown compound
Show the ionic equation of the sulphate test
Ba2+(aq) + SO4^2-(aq) ——> BaSO4(s)
what happens if you put barium chloride or barium nitrate instead of barium ions
you can carry out a halide test when using barium nitrate
with barium chloride you are introducing chloride ions to your solution
what happens in a halide test
most halides are soluble but silver halides are insoluble .
Aqueous silver ions react with halide ions to form precipitate’s of silver halides
whats the general equation of halide tests
Ag+(aq) + X-(aq) —–> AgX(s)
what do you do in halide test
1) add aq silver nitrate AgNO3 to an aq solution of a halide
2)the silver halide percipitates are different colours
3) add aq ammonia to test
what colours are the silver halide percipitates
Fluorides produce no precipitate
Chlorides produce a white precipitate
Ag+(aq) + Cl- (aq) AgCl(s)
Bromides produce a cream precipitate
Ag+(aq) + Br- (aq) AgBr(s)
Iodides produce a pale yellow precipitates
what is the sequence of tests for anions
carbonate
sulphate
halides
why is the carbonate test first
because in the carbonate test you add dilute nitric acid and are looking for effervescence of CO2 gas
neither sulphate or halide produces bubbles with dilute nitric acid. The carbonate test can be carried out without the possibility of an incorrect conclusion
If the test produce no bubbles then no carbonate ion is not present you may proceed to the next test
whats the next test
Sulfate test you added solution containing Ba2+(aq) ions and are looking for a white precipitate of BaSO4
Barium carbonate, BaCO3 is white and insoluble in water. So if you carry out a sulfate test on a carbonate you will get a white precipitate too. Therefore its important to carry out the carbonate test first than sulfate when you know that no carbonate is present
Why is the Halide test last
in the halide test you add a solution containing Ag+(aq) ions as AgNO3(aq) and are looking for a precipitates.
Silver carbonate AgCO3 and silver sulfate Ag2SO4, are both insoluble in water and will form as precipitates in this test. It is therefore important to carry out the halide test last after carrying carbonate and sulfate test to rule out thosepossibilites
what are the test for cations+
test for ammonium ion NH4^+
what happens in the test for ammonium ions
when heated heated together aqueous ammonia ions and aqueous hydroxide ions react to form ammonia gas NH3
NH4^+(aq) + OH-(aq) —–> NH3 (g) + H2O(l)
how is the test of ammonium ions carried out
1)Aqueous sodium hydroxide ,NaOH is added to a solution of an ammonium ion
2)Ammonia gas is produced. You are unlikely to see gas bubbles as ammonia is very soluble in water
3)The mixture is warmed and ammonia gas is released
4)You may able to smell ammonia but its easy to test with gas with moist indicator paper. Ammonia is alkaline and its presence will turn the paper blue
Barium chloride is soluble in water compared to the electrical conductivities of solid and aqueous barium chloride
Barium chloride does not conduct electricity when solid and because it has ions which are fixed ( in lattice)
Barium chloride conducts when aqueous solution because it has mobile ions
What is barium chloride used for
To test for sulfates and produce white percipitate
Name an apparatus to seperate two liquid layers present at the end of an experiment
Separating funnel
What do experimental results tell you about the carbon halogen bond enthalpy
Decrease down the group so chlorine- carbon atoms are the strongest
How could students modify their hydrolysis experiment so it could be completed in less time
By heating the test tube in water bath
