qualitative analysis Flashcards
(18 cards)
what reagent is used for the carbonate test
dilute nitric acid
what is the equation for the carbonate test
2HCl + Na2CO3 2NaCl + H2O + CO2
what is a positive result for the carbonate test
gases produced, efferverescence
how to prove gas produced in carbonate test is carbon dioxide
- add Ca(OH)2
-limewater turns cloudy
equation for positive test for confirmation of CO2 in carbonate test
CO2(g) + Ca(OH)2(aq)—> CaCO3(g)+H2O(l)
what reagant is used in test for sulfate ions and why
aqueous barium
- BaNO3
because barium suldate is insoluble in water and so forms white solid precipitate
positive test result for test for sulfate ions
white precipitate
ionic equation for test for sulfate ions
Ba+(aq) + SO4 2- (aq) —> BaSO4(s)
what reagant is used for test for halides and why
Ag+ ions
- AgNO3
silver halides insoluble in water–> precipitate
what are the positive test results for the halide test
silver chloride–> white
silver bromide–> cream
silver iodide–> yellow
how to test solubility of precipitate in the halide test
add dilute ammonia–> silver chloride dissolves in dilute ammonia but others arent
add concentrated ammonia–> silver bromide dissolves in concentrated ammonia but the others dont
chemical reaction between silver chloride and ammonia
AgCl(s) + 2NH3(aq) –>[Ag(NH3)2]+(aq) + Cl- (aq)
what is the test for ammonium ions
-add aqueous NaOH
-warm mixture and ammonia gas is released
-use damp litmus paper to test pH of gas
- paper will turn blue
ionic equation for test for ammonium ions
NH4+(aq) + OH-(aq) —> NH3(g) +H2O(l)
what is the sequence of tests for ions
- carbonate test
- sulfate test
- halide test
why should the carbonate test be carried out first
the carbonate test can be carried out without the possibility of a false result
-because sulfate and halide ions dont produce bubbles with dilute acid
- prevents formation of AgCO3 which will give false halide test result
why is sulfate test carried out before halide test and after carbonate test
why is the halide test carried out last
AgSO4 and AgCO3 forms precipitates and so will give false positive result
