chemical analysis (topic 8) Flashcards
describe how to complete a flame test (2)
- place clean wire into solid being tested or place damp splint into solid
- hold wire in bunsen flame and observe colour of flame produced
what colour flame is produced when a sample containing copper ions undergoes a flame test
green
what colour flame is produced when a sample containing sodium ions undergoes a flame test
yellow
a student wishes to identify the metal in a metal chloride solid sample, she thinks the metal could be sodium, potassium, calcium or aluminium, describe the tests that can be performed to indicate the presence of each of these metal ions (6)
flame tests:
- sodium, potassium, and calcium ions detected by flame test
- clean flame test wire with hydrochloric acid
- dip wire into solid
- yellow flame if the metal is sodium
- lilac flame if the metal is potassium
- orange-red flame if the metal is calcium
- no flame colour - the metal could be aluminium
precipitates formed with sodium hydroxide solution:
- calcium and aluminium ions detected using sodium hydroxide solution
- dissolve white solid in water
- add drops of sodium hydroxide solution
- white precipitate shows calcium or aluminium ions
- no precipitate shows sodium or potassium ions
- add more drops sodium hydroxide solution
dissolving precipitate with more sodium hydroxide:
- if the white precipitate dissolves to form a colourless solution - aluminium ions
- if the white precipitate precipitate does not dissolve - calcium ions
hydrochloric acid is added to the solid being tested, carbon dioxide is given off, state what must be present in the substance
carbonate ion
describe the test for chloride ions and state the colour of the precipitate formed (2)
- add dilute nitric acid followed by silver nitrate solution
- white precipitate is formed
the student tests for iodide ions by adding dilute nitric acid, followed by silver nitrate solution, state the colour of the precipitate formed if iodide ions are present
yellow
hydrochloric acid is added to the solid, followed by barium chloride solution, white precipitate forms, state what ion must be present in the solid
sulfate ions
describe how the student could test to see if any of the gases is carbon dioxide (2)
- add limewater
- limewater turns cloudy if the gas is carbon dioxide
- bubble gas produced through limewater
- limewater will turn cloudy when carbon dioxide bubbles through
describe the test for chlorine gas (2)
- damp litmus paper held in test tube containing gas
- if the paper is bleached white, chlorine is present
describe how to test for halides (3)
- add dilute nitric acid
- followed by silver nitrate
- if halides are present a precipitate will form
state the name of the halide ions found in the other samples
- sample 1 - chloride ions
- sample 2 - iodide ions
- sample 4 - bromide ions
write the balanced chemical reaction for the reaction between sodium chloride and silver nitrate (AgNO3)
write a balanced chemical equation for the reaction between copper carbonate and sulfuric acid
describe how the student would know when the chemical reaction has stopped, copper carbonate and sulfuric acid (4)
- bubbling stops or no more gas produced
- no fizzing
- no further changes in colour
- no more copper carbonate dissolves and sinks to the bottom of flask or no more copper carbonate left as it has been used up in the reaction
write a balanced symbol equation for the reaction between sodium and water
sulfates
an orange-red flame will appear if potassium ions are present
