Chemical Tests Flashcards
Describe the method of conducting a flame test.
- Dip a piece of nichrome/platinum wire into hydrochloric acid.
- Dip the wire into a sample of solid or solution. This causes some of the sample to stick onto the wire.
- Place the tip of the wire into a non-luminous Bunsen flame.
Describe the method of conducting a flame test.
- Dip a piece of nichrome/platinum wire into hydrochloric acid.
- Dip the wire into a sample of solid or solution. This causes some of the sample to stick onto the wire.
- Place the tip of the wire into a non-luminous Bunsen flame.
What metal cation produces a red flame in a flame test?
Lithium
What metal cation produces a yellow flame in a flame test?
Sodium (Na)
What metal cation produces a lilac flame in a flame test?
Potassium
What metal cation produces an orange-red flame in a flame test?
Calcium
What metal cation produces a blue-green flame in a flame test?
Copper
Describe the test for cations using sodium hydroxide solution.
Dissolve the salt in distilled water and put about 1cm3 in a test tube. The solution will go cloudy as a solid forms.
What is the colour of the precipitate of copper hydroxide?
Blue
What is the colour of the precipitate of iron (II) hydroxide?
Green
What is the colour of the precipitate of iron (III) hydroxide?
Brown
Describe the method of conducting an ammonium test.
Dissolve the sample in water
Add some NaOH (aq)
Test the gas evolved with damp red litmus paper.
If NH4 + ions are present in the original sample the litmus paper will turn blue.
Describe the test for halide ions using the silver nitrate test.
Dissolve the sample in water
Add nitric acid (HNO3)
Add silver nitrate (AgNO3) solution
If Cl-, Br-, I- ions are present, a precipitate forms.
What precipitate has a white colour?
AgCl
What precipitate has a cream colour?
AgBr
What precipitate has a yellow colour?
AgI
Why is it important to add Nitric acid into the silver nitrate test?
Because silver ions also form precipitates with other anions like hydroxide and carbonate. The nitric acid reacts with those anions preventing false positives.
Describe the method of a test for carbonates.
Add hydrochloric acid, look for effervescence.
If there is effervescence, bubble the gas through limewater.
If CO3 2- ions were present in the sample, the has evolved turns into limewater cloudy.
Why is platinum a suitable metal to use as the wire in a flame test?
It has a high melting point
It doesn’t effect the colour of the flame
