C4.2 - Identifying The Products Of Chemical Reactions Flashcards
How can you detect carbon dioxide and what is the change caused by?
- You can test for carbon dioxide using limewater
(calcium hydroxide solution). - Limewater turns cloudy white when carbon
dioxide is bubbled through it. - The change is caused by calcium hydroxide
reacting with carbon dioxide to form water and
a white precipitate of calcium carbonate.
How can you detect chlorine gas?
- Chlorine dissolves in water to form an acidic
solution. - Chlorine bleaches dyes.
- Use a drop of tap water to dampen a piece of blue
litmus paper. - Hold the paper near to a container that holds the
substance. - If chlorine is present, the paper turns red then
white.
How do you smell substances in the laboratory?
- With the container well away from your nose,
breathe in enough air to almost fill your lungs. - Hold the container a few centimetres away from
your nose, and waft any smell towards you. - Take a cautious sniff.
How can you detect hydrogen and oxygen?
Hydrogen - Place a lighted splint near the mouth of the container of gas - If hydrogen is present, a squeaky pop noise will occur.
Oxygen - Place a glowing splint near the mouth of the container of gas - If oxygen is present, the splint should relight.
What is the basis of a flame test?
- Metal ions are heated, energy is transferred to
their electrons. - This makes their electrons move into higher
electron shells. - When the electrons move back to their normal
electron shells, energy is transferred to the
surroundings as radiation, which you see as light.
What are the steps for carrying out a flame test?
- Clean a wire loop attached to a handle several
times by dipping it into hydrochloric acid, then
rinsing it with distilled water. - Once it is clean, there will be no change in the
colour of the Bunsen burner flame when you hold
the loop in it. - Dip the clean loop into the test powder or solution.
- Use the handle to hold the loop in the edge of a
roaring blue flame. - Record the flame colour.
What is the purpose of cleaning the wire loop between each flame test?
- To ensure it is not contaminated with the
previous sample. - So you will not confuse flame colours or mix
them.
What are the flame test colours?
- Lithium - Li+ - Red
- Sodium - Na+ - Yellow
- Potassium - K+ - Lilac
- Calcium - Ca2+ - Orange/Red
- Copper - Cu2+ - Green/Blue
What are hydroxide precipitate tests?
- Different metals produce different coloured
precipitates. - Add a few drops of sodium hydroxide solution to a
solution containing metal ions. - Note the colour of any precipitate formed.
What are the different hydroxide precipitate test colours?
Iron(II) - Green Iron(III) - Orange/Brown Copper(II) - Brown Calcium - White Zinc - White
How can you tell whether the metal ion is zinc or calcium in a hydroxide precipitate test?
- Add excess sodium hydroxide solution.
- Zinc hydroxide dissolves to form a colourless
solution. - Calcium hydroxide does not dissolve.
How do you detect sulphate ions?
- Add a few drops of hydrochloric acid.
- Then add a few drops of barium chloride solution.
- If sulphate ions are present you would get a white
precipitate of barium sulphate.
How do you detect carbonate ions?
- Hydrogen ions from dilute acids react with
carbonate ions to produce carbon dioxide and
water. - Add a few drop of hydrochloric acid.
- If carbonate ions are present, bubbles of gas
will be produced. - You can confirm the gas is carbon dioxide by
bubbling it through limewater.
How do you detect halide ions?
- Add a few drops of nitric acid.
- Then add a few drops of silver nitrate solution.
- Chloride ions - Silver chloride - White
- Bromide ions - Silver bromide - Cream
- Iodide ions - Silver iodide - Yellow
Why does the halide ion test not work for fluoride ions?
Silver fluoride is soluble in water.
Why is the carbonate ions test useful?
- It works whether the carbonate compound is in the
solid state or in a solution. - This is useful because most carbonates are
insoluble.
What are the half equations for a positive sulphate ion and carbonate ion test?
Ba2+ (aq) + SO42- (aq) -> BaSO4 (S)
2H+ (aq) + CO32- (aq) -> CO2 (g) + H2O (l)
What are instrumental methods of analysis?
A technique for analysing a substance that depends upon a machine.
What are some advantages of instrumental methods of analysis compared to chemical methods?
- Sensitivity - Instruments can analyse very small
amounts of substances. Useful if the substance is
difficult or expensive to obtain. - Accuracy - Instruments are very accurate. Can be
calibrated using internationally accepted
standards. - Speed - Instruments can carry out analysis quickly
and they can run all the time.
What is a gas chromatogram and how do you interpret them?
- A gas chromatogram is a chart that represents
the different substances in a mixture. - Each peak represents a substance present in
the mixture. - The areas under each peak show the relative
amount of each substance in the mixture. - The retention time, the time taken for each
substance to travel through the chromatography
column, is different for different substances.
What is a mass spectrometer?
- A machine that can measure masses of atoms and
molecules. - Used to analyse the relative amounts of different
isotopes of an element and the structure of
molecules.
What are the four steps that occur in a mass spectrometer?
1) Ionisation
- Atoms bombarded with electrons.
- The electrons collide with the atoms to give a 1+
charge which makes the fragments unstable.
2) Acceleration
- All the fragments are made to have the same KE.
3) Deflection
- The fragments are passed through a magnetic
field and deflect proportionate to their mass and
charge.
4) Detection
- The beams of fragments are detection
electronically.
- It detects how much of the mass is deflected and
whether the sample is a pure substance.
How do you interpret a mass spectrum?
- Relative abundance against the mass to charge
ratio. - Each peak represents a fragment of the molecule.
- The peak on the far right represents the molecular
ion. - The mass to charge ratio of the molecular ion
peak is equal to the relative formula mass, Mr, of
the molecule.
