Tests for gases, anions & cations Flashcards
what safety precautions are required for testing chlorine gas?
(2 marks)
- do the experiment in a fume cupboard
- wear a gas mask
how do you test for chlorine gas?
expose it to damp blue litmus paper
what happens when damp blue litmus paper is exposed to chlorine gas?
the damp litmus paper turns red, the bleaches white
how do you test for oxygen gas?
expose it to a glowing splint
what happens when a glowing splint is exposed to oxygen gas?
the glowing splint will relight
how do you test for hydrogen gas?
expose it to a lit splint
what happens when hydrogen gas is exposed to a lit splint?
there is a squeaky pop sound
how do you test for carbon dioxide gas?
bubble it through limewater
what happens when you bubble carbon dioxide gas through limewater?
limewater turns milky / cloudy white
how do you test for carbonate ions?
- in a test tube, add some dilute HCl to the sample compound
- bubble the gas produced through limewater
- limewater will turn cloudy white due to presence of carbon dioxide gas
- this means the sample compound was a carbonate, because:
- carbonates produce CO2 gas when reacted with HCl
- React the substance with hydrochloric acid (HCl).
- If the substance contains a carbonate ion, carbon dioxide gas will bubble out of the solution.
- Collect the gas and bubble it through limewater.
If the limewater turns cloudy, it confirms the gas is carbon dioxide. - Confirmation that the gas is carbon dioxide is confirmation that the original substance contained carbonate ions.
how do you test for sulfate ions?
- in a test tube, add dilute HCl to the sample (to remove any carbonate or sulfite ions in the sample, which are impurites - they could also react with the barium ions to forma white precipitate, which would confuse the results)
- add barium chloride solution (BaCl2)
- it will react with the sulphate ions in the sample (if there are any present), forming barium sulfate, a WHITE PRECIPITATE
- React the substance with hydrochloric acid (HCl) to remove any carbonate ions.
- Add barium chloride solution.
- If sulfate ions are present, it will form a white precipitate of barium sulfate.
how do you test for halide ions?
- in a test tube, add dilute NITRIC acid to the test sample (to remoce any carbonate and sulfite ions)
- add silver nitrate
- silver ions will react with halide ions (if any are present) in the test sample, forming a precipitate; the precipitates are different colours depending on which halide ions are in the sample:
- silver CHLORIDE = WHITE precipitate
- silver BROMIDE = CREAM precipitate
- silver IODIDE = YELLOW precipitate
- React the solution with nitric acid to remove any carbonate ions or sulfite ions.
- Add silver nitrate solution.
- If a white precipitate forms, the substance contains chloride ions.
- If a cream precipitate forms, the substance contains bromide ions.
- If a yellow precipitate forms, the substance contains iodide ions.
A chemical reaction is taking place in a test tube. What methods could be used to collect the gas?
(2 marks)
- Place an upside down measuring cylinder over the test tube to trap the gas
- Attach the top of the test tube to a gas syringe
When testing for sulfate ions, why do we have have to add hydrochloric acid first?
To react with any carbonate ion impurities
An unknown solution is mixed with nitric acid, and then silver nitrate. A cream precipitate forms.
Which anion did the solution contain?
bromide ions
