Methods of Identifying Ions (AQA GCSE Chemistry)
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What is a flame test used for?
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What is a flame test used for?
A flame test is used to identify metal ions by the colour of the flame they produce when heated.
True or False?
The Bunsen burner flame should be on a blue flame for flame tests.
True.
The Bunsen burner flame should be on a blue flame for flame tests as this is the hottest flame.
Give the flame colour produced by sodium ions.
The flame colour produced by sodium ions is yellow.
Give the flame colour produced by copper(II) ions.
The flame colour produced by copper(II) ions is green.
True or False?
The flame colour produced by potassium ions is pink.
False.
The flame colour produced by potassium ions is lilac.
Give the flame colour produced by calcium ions.
The flame colour produced by calcium ions is orange-red.
True or False?
The flame colour produced by lithium ions is red.
False.
The flame colour produced by lithium ions is crimson.
Why is the nichrome wire first dipped in hydrochloric acid?
The nichrome wire is first dipped in hydrochloric acid to avoid contamination.
True or False?
If a sample has a mixture of ions, some flame colours can be masked.
True.
If a sample has a mixture of ions, some flame colours can be masked.
Define the term cation.
A cation is a positively charged metal ion.
What colour precipitate is formed when sodium hydroxide is added to a solution containing copper(II) ions?
The colour of the precipitate formed when sodium hydroxide is added to a solution containing copper(II) ions is blue.
True or False?
Iron(III) ions form a green precipitate in the presence of sodium hydroxide.
False.
Iron(III) ions form a brown precipitate in the presence of sodium hydroxide.
What colour precipitate is formed when sodium hydroxide is added to a solution containing iron(II) ions??
The colour of the precipitate formed by iron(II) ions in the presence of sodium hydroxide is green.
True or False?
Ca2+ ions form a red precipitate in the presence of sodium hydroxide.
False.
Ca2+ form a white precipitate in the presence of sodium hydroxide.
True or False?
The green precipitate formed by Cr3+ ions will not dissolve in excess sodium hydroxide solution.
False.
The green precipitate formed by Cr3+ ions will dissolve in excess sodium hydroxide solution to give a green solution.
Describe the tests using sodium hydroxide that will distinguish between solutions containing Al3+ ions, Ca2+ ions and Mg2+ ions.
The tests using sodium hydroxide to distinguish between solutions containing Al3+ ions, Ca2+ ions and Mg2+ ions:
All solutions will give a white precipitate with sodium hydroxide solution
When excess sodium hydroxide is added, the precipitate containing Al3+ ions will dissolve, but the one with Ca2+ and Mg2+ will not
A flame test will produce an orange-red flame with Ca2+
Define the term anion.
An anion is a negatively charged ion.
What is the formula of a carbonate ion?
The formula of a carbonate ion is CO32-.
Describe the test and result for carbonate ions.
The test for carbonate ions is:
Add dilute hydrochloic acid and test the gas produced by bubbling it through limewater.
If carbonate ions are present, carbon dioxide is produced which turns limewater cloudy.
Describe the test and result for bromide ions.
The test and result for bromide ions is:
Add dilute nitric acid followed by silver nitrate solution
A cream precipitate is formed
Describe the test and result for iodide ions.
The test and result for iodide ions is:
Add dilute nitric acid followed by silver nitrate solution
A yellow precipitate is formed
True or False?
Chloride ions give a white precipitate with acidified silver nitrate solution.
True.
Chloride ions give a white precipitate with silver nitrate solution.
When acidified silver nitrate solution is added to a sample containing bromide ions, a precipitate of silver bromide is formed.
What is the state symbol for this precipitate?
The state symbol for the precipitate of silver bromide is s.
Give the formula of the precipitate formed when silver nitrate solution is added to a solution containing iodide ions.
The formula of the precipitate formed when silver nitrate solution is added to a solution containing iodide ions is AgI.
Write the ionic equation for the formation of a precipitate of silver bromide, including state symbols.
The ionic equation for the formation of a silver bromide precipitate, including state symbols is:
Ag+(aq) + Br-(aq) → AgBr (s)
What are halide ions?
Halide ions are the ions formed by elements in Group 7.
Why must the sample being tested for halide ions be acidified with nitric acid and not hydrochloric acid?
Hydrochloric acid cannot be used to acidify a sample prior to testing it for halide ions as it contains chloride ions, which would give a false positive result.
What is the formula of silver nitrate solution?
The formula of silver nitrate solution is AgNO3.
What is the formula of the sulfate ion?
The formula of the sulfate ion is SO42-.
True or False?
To test for sulfate ions, acidified berylium chloride is used.
False.
To test for sulfate ions, acidified barium chloride is used.
Name the white precipitate formed during a positive test for sulfate ions.
The white precipitate formed during a positive test for sulfate ions is barium sulfate.
Describe the test and result for sulfate ions.
The test and result for sulfate ions is:
Add dilute hydrochloric acid followed by barium chloride solution.
A white precipitate will form.
Write the ionic equation for the formation of barium sulfate, including state symbols.
The ionic equation for the formation of barium sulfate, including state symbols is:
Ba2+ (aq) + SO42- (aq) → BaSO4 (s)
Why is hydrochloric acid added to a sample before barium chloride solution when testing for sulfate ions?
Hydrochloric acid added to a sample before barium chloride solution when testing for sulfate ions because it removes any carbonate ions which might be present and interfere with the results.
Name one method of instrumental analysis.
One method of instrumental analysis is flame emission spectroscopy.
Give two advantages of instrumental analysis over traditional methods of chemical analysis.
Advantages of instrumental analysis over traditional methods of chemical analysis include:
It is faster
It is more sensitive
It is more accurate
How does flame emission spectroscopy work?
Flame emission spectroscopy works by exposing the sample to a very hot flame and then measuring the intensity and wavelength of the light emitted.
How can ions in unknown samples be identified using flame emission spectroscopy?
Ions in unknown samples can be identified using flame emission spectroscopy by comparing the sample spectrum to reference spectra.
True or False?
Unknown salt X contains rubidium ions.
False.
Unknown salt X does not contain rubidium ions.
True or False?
Unknown salt X contains potassium ions.
True.
Unknown salt X contains potassium ions
True or False?
Unknown salt X contains three ions in total.
True.
Unknown salt X contains three ions in total: sodium, potassium and an unknown.