Chemical analysis Flashcards
(28 cards)
What is a pure substance?
Substance without anything added to it (only one element or compound)
How can you tell how pure a substance is?
A pure substance will melt or boil at a specific temperature so its purity can be tested by measuring a substance’s melting/boiling point and comparing the value to the melting/boiling point of a pure substance. The closer it is to the value, the purer it is. The larger the range is, the less pure it is.
What are formulations?
Mixtures with a precise purpose made by following a formula, eg. paint
How do you test for chlorine?
Chlorine bleaches damp litmus paper, turning it white.
How do you test for oxygen?
In the presence of oxygen, a glowing splint will relight.
How do you test for carbon dioxide?
In the presence of carbon dioxide, lime water will turn cloudy.
How do you test for hydrogen?
Squeaky pop test
If a burning splint is held above hydrogen, there will be a squeaky pop.
Explain chromotography
- draw a line in pencil towards the bottom of a piece of chromatography paper
- add the samples of ink to the line
- put the sheet in a beaker with some solvent (water) at the bottom so that the pencil line isn’t in the water
Rf =
Distance moved by substance
_______________________
Distance traveled by solvent
How can you test for carbonates (substances containing CO3 2- ions)?
To test for carbonates, you can add a few drops of a dilute acid to the substance. This test tube should be connected to another test tube, containing lime water. If it is a carbonate, carbon dioxide will be produced and the lime water will turn cloudy.
How can you test for sulfates (substances containing SO4 2- ions)?
A few drops of dilute hydrochloric acid and barium chloride solution are added. If sulfate ions are present, a white precipitate is formed.
How can you test for halides?
Add a couple of drops of dilute nitric acid and silver nitrate solution.
Chloride gives a white precipitate.
Bromide gives a cream precipitate.
Iodide gives a yellow precipitate.
When testing for halides, what colour precipitate does chloride give you?
White
When testing for halides, what colour precipitate does bromide give you?
Cream
When testing for halides, what colour precipitate does iodide give you?
Yellow
How can you identify metal ions?
Some metal compounds produce a distinctive colour when heated in a flame by using a nichrome wire (cleaned by a flame first) to holg the metal in the flame.
What colour flame does a lithium ion produce?
Crimson flame
What colour flame does a sodium ion produce?
Yellow flame
what colour flame does a potassium ion produce?
Lilac flame
What colour flame does a calcium ion produce?
Orange-red flame
What colour flame does a copper ion produce?
Green flame
How can you identify metal hydroxides?
Some metal hydroxides are insoluble and produce a precipitate with a characteristic colour. To test this, a few drops of sodium hydroxide need to be added to the unknown substance.
What colour precipitate does a calcium ion produce when sodium hydroxide is added to it?
White precipitate
What colour precipitate does a copper ion produce when sodium hydroxide is added to it?
Blue precipitate
