Flashcards
8.3 Qualitative analysis
Flashcards do conjunto (48)
- 1What does qualitative analysis rely on?Simple observations rather than measurements
- 2Give example of a quantitaative analysis? And what does it mean?Titration
Technique with numerical results - 3What could the qualitative analysis observations be?- Gas bubbles
- Precepitates
- Colour changes
- Identification of gases - 4Name a test for anion based on gases.Carbonate test
- 5Carbonates react with acids to form what gas?Carbon dioxide
- 6Write the equation of dilute nitric acid with aqueous sodium carbonate.Na2CO3(aq) + 2HNO3(aq) → 2NaNO3(aq) + CO2(g) + H2O(l)
- 7What is the carbonate ion?CO3^2-
- 8How would you test for the carbonate ion?1) In a test tube, add dilute nitric acid to the solid or solution to be tested.
2) If you see bubbles, the unknown compound could be a carbonate
3) Test for CO2 - 9How do you carry out a test to prove that carbon dioxide is gas.- Bubble the gas through lime water - a saturated aqueous solution of calcium hydroxide, Ca(OH)2
- Carbon dioxide reacts to form a white precipitate of calcium carbonate, which turns the lime water cloudy - 10Write the equation for carbon dioxide being added to calcium hydroxide. (Lime water test)Co2(g) + Ca(OH)2(aq) → CaCO3(s) + H2O(l)
- 11What are the two tests based on precipitates?Sulfate test
Halide test - 12Most sulfates are soluble in water, but which sulfate isn't?Barium sulfate, BaSO4
very insoluble - 13What is formed in sulfate test?White precipitate of barium sulfate
- 14Write the ionic equation for Ba and sulfate.Ba^2+(aq) + SO4^2-(aq) → BaSO4(s)
- 15How are the Ba^2+ ions added?Aqueous barium chloride or barium nitrate
- 16If you intend to carry out a halide test afterwards a sulfate test what do you use?Barium nitrate
(Not barium chloride becaue you are introducing chloride ions to your solution) - 17Most halides are soluble in water so what halides are used?Silver halides are insoluble
- 18Aqueous what ions with what other aqueous ions form precipitates?Aqueous silver ions react with aqueous halide ions to form precipitates
- 19Write the general equation for halide tests (silver halides) use X-(aq) to represent an aqueous solution of any halide.Ag+(ag) + X-(aq) → AgX(s)
- 20Write out the steps on how you would carry out an halide test.1) Add aqueous silver nitrate, AgNO3, to an aqueous solution of a halide.
2) The silver halide precipitates are different colours - silver chloride is white, silver bromide is cream-coloured, and silver iodide is yellow.
3) Add aqueous ammonia to test the solubility of the precipitate. - 21Why is important for add aqueous ammonia to test the solubility of the precipitate (step 3 in halide test)?The three precipitate colours can be difficult to tell apart.
- 22Write the ionic equation for chloride, Cl- with silver halide.Ag+(aq) + Cl-(aq) → AgCl(s)
- 23Write the ionic equation for bromide, Br- with silver halide.Ag+(aq) + Br-(aq) → AgBr(s)
- 24Write the ionic equation for iodide, I- with silver halide.Ag+(aq) + I-(aq) →
- 25What is colour of precipitate for chloride, Cl-?White
- 26What is the colour of precipitate for bromide, Br-?Cream
- 27What is the colour of precipitate for iodide, I-?Yellow
- 28What is the solubility in NH3(aq) for chloride, Cl-?Soluble in dilute NH3(aq)
- 29What is the solubility in NH3(aq) for bromide, Br-?Soluble in conc. NH3(aq)
- 30What is the solubility in NH3(aq) for iodide, I-?Insoluble in conc. NH3(aq)
- 31Barium ions in solution are extremly toxic. Why are patients not poisoned by this treatment?Barium sulfate is very insoluble in water, so passes through the body without interacting with it.
- 32What is the correct order to analyse an unknown organic compound?1) Carbonate, CO3^2-
2) Sulfate, SO4^2-
3) Halides, Cl-, Br- and I- - 33Why is there a correct order for the carbonate test to go first?- You add dilute acid and are looking for bubbles from CO2 gas
- Neither sulfate or halide ions produce bubbles with dilute acid
- Carbonate test can be carried out without the possibility of an incorrect conclusion
- If test has no bubbles, then no carbonate is present (next test) - 34Why is there a correct order for the sulfate test to come second?- In sulfate test, you add a solution containing Ba^2+(aq) ions and are looking for a white precipitate of BaSO4(s)
- Barium carbonate, BaCO3, is white and insoluble in water - if you carry out a sulfate test on a carboate, you will get a white precipitate too
- IMPORTANT - carry out carbonate test first and only proceed to sulfate test when you know no carbonate is present - 35Why is there a correct order for the halide test to come last?- You add a solution containing Ag+(aq) ions, as AgNO3(aq), and are looking for a precipitate
- Silver carbonate, Ag2CO3 and silver sulfate, Ag2SO4, are both insoluble in water and will form as precipitates in this test - 36If you were asked to analyse a mixture of chemicals what do you do?Carry out the tests in the same sequence and on the same solution.
- 37What do you do for the carbonate test when asked to analyse a mixture of chemicals?- If you see bubbles, continue adding dilute nitric acid until the bubbling stops
- All carbonate ions will then have been removed and there will be none left to react in the next tests - 38If you intend to test for sulfate or halide ions, it is important to use what for carbonate test?Dilute nitric acid, HNO3
- 39Why shouldn't you use hydrochloric acid or sulfuric acid for the carbonate test and have to use nitric acid instead?Sulfuric acid contains sulfate ions
Hydrochloric acid contains chloride ions
Which will show up in the sulfate and halide tests - 40How do you use the sulfate test to analyse a micture of chemicals?- To the solution left from the carbonate test, add an excess of Ba(NO3)2(aq)
- Any sulfate ions present will precipitate out as barium sulfate
- Filter the solution to remove the barium sulfate - 41Why is it important to not use BaCl2 if you intend to test for halide ions?Chloride ions will show up in the halide test
- 42How do you carry out the halide test when asked to analyse a mixture of chemicals?- To the solution left from the sulfate test, add AgNO3(aq)
- Any carbonate or sulfate ions initially present have already been removed. Any precipitate formed must involve halide ions.
- Add NH3(aq) to confirm which halide you have. - 43What is the test for cations?Test for ammonium ions, NH4+
- 44Write the equation for: When heated together, aqueous ammonium ions and aqueous hydroxide ions react to form ammonia gas, NH3.NH4+(aq) + OH-(aq) → NH3(g) + H2O(l)
- 45Based on: NH4+(aq) + OH-(aq) → NH3(g) + H2O(l) How would you test for the ammonium ions?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) Smell ammonia, test the gas with moist pH indicator paper. Ammonia is alkaline and its presence will turn the paper blue. - 46How could you distinguish between NaCl, NaBr and NaI by a simple test? (3)Add AgNO3(aq) to an aqueous solution of each. NaCl forms a white precipitate which dissolves in dilute NH3(aq)
NaBr forms a cream precipitate which dissolves in concentrated NH3(aq)
NaI forms a yellow precipitate which is insoluble in concentrated NH3(aq) - 47Explain why it is important to carry out the carbonate test before carrying out a sulfate test on an unknown chemical. (2)Dilute nitric acid reacts wth carbonate ions and no precipitate of barium carbonate will then form.
- 48Explain why, if you are testing a mixture, it is important to use dilute nitric acid, rather than sulfuric or hydrochloric acid, for the carbonate test.If sulfuric acid is used, sulfate ions are added and will show up in the sulfate test with Ba^2+(aq).
If hydrochloric acid is used, chloride ions are added and will show up in the halide test with Ag+(aq)
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- A level Chemistry (Module 3: Periodic table and energy) FlashCards sobre 8.3 Qualitative analysis, criado por Urvi B em 06-01-2018.
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- Urvi B
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