GCSE Chemistry: Chemical Analysis
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30 Terms
What is the test for chlorine?
Bleaches damp litmus paper
What is the test for hydrogen?
Put a lit splint where the gas is and if there's a squeaky pop, hydrogen is present.
What is the test for carbon dioxide?
Run the gas through limewater and if it turns cloudy, carbon dioxide is present.
What is the test for oxygen?
Relights a glowing splint
What is a pure substance?
A single element or compound, not mixed with any other substance
What is a mixture?
A combination of two or more substances that are not chemically combined
What is a formulation?
a mixture that has been designed as a useful product
What are the two phases in chromatography?
Mobile phase: where the molecules can move (liquid or gas)
Stationary phase: where molecules can't move (solid or really thick liquid
What determines how far a substance travels in chromatography?
The relative attraction the the paper and the solvent.
If a substance has a stronger attraction to the solvent, will it have a high or low Rf value?
High
Why is pencil used in chromatography?
It does not dissolve in the solvent.
How and why must you clean a nichrome wire before a flame test?
To remove any cations that may distort results. Flame the end of the wire and dip in hydrochloric acid.
Where should the ionic compound be burnt in the bunsen flame?
In the outside edge
What does a crimson red flame indicate?
Li+ ions are present
What does a yellow-orange flame indicate?
Na+ ions are present
What does a lilac flame indicate?
K+ ions are present
What does a red-orange flame indicate?
Ca2+ ions are present
What does a green flame indicate?
Cu2+ ions are present
How can NaOH be used to identify cations?
When a solution being tested for cations is mixed with NaOH solution, a precipitate may form which can be used to identify which cation is present.
What is a precipitate?
a solid formed when two solutions react.
What does a blue precipitate indicate?
Copper(II) Cu2+ ions are present
What does a green precipitate indicate?
Iron(II) Fe2+ ions are present
What does a brown precipitate indicate?
Iron(III) Fe3+ ions are present
What is special about the precipitate formed by aluminium ions?
Excess precipitate redissolves
Describe the test for carbonate ions
Add dilute hydrochloric acid then bubble any gas produced through limewater. If carbonate is present, solution fizzing, lime water goes cloudy (white precipitate is formed).
Describe the test for sulfate ions
Add HCl to remove any CO3 2- ions which would obscure the results
Add a couple of drops of barium chloride
If sulfate ions are present, a white precipitate of barium sulfate will form
Describe the test for halide ions
Add nitric acid to remove any carbonate ions. Add silver nitrate. Observe the colour of the precipitate
What colour precipitate indicates Cl- ions are present?
White
What colour precipitate indicates Br- ions are present?
Cream
What colour precipitate indicates I- ions are present?
Yellow
Note 
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