Chemical analysis Flashcards
What is a pure substance?
A substance that only contains one element or compound
How can you identify a pure substance?
By its melting/boiling point
How can you tell if a substance is impure?
If its melting/boiling point is over a range of temperatures
What is chromatography used for?
The separation of mixtures to identify their components
What is the stationary phase in chromatography?
The paper
What is the mobile phase in chromatography?
The water or solvent
How do you calculate the Rf value in chromatography?
Distance moved by substance / distance moved by solvent
How do you test for hydrogen?
A burning splint is held at the open end of a test tube of the gas, if hydrogen is present it will make a squeaky pop sound
How do you test for oxygen?
A glowing splint is inserted into a test tube of the gas, the splint will relight if oxygen is present
How do you test for carbon dioxide?
Bubbling the gas through limewater (calcium hydroxide), the limewater will turn from clear to cloudy if carbon dioxide is present
How do you test for chlorine?
Damp litmus paper is put into the gas, it will bleach and turn white if chlorine is present
What are the two ways you can test for metal ions?
Flame tests and drops of sodium hydroxide solution
What colour does each metal burn:
Lithium
Sodium
Potassium
Calcium
Copper
Crimson
Yellow
Lilac
Orange-red
Green
Why might a flame test not work?
If the substance is impure then some colours can be masked by other brighter colours
What is the method for a flame test?
1) Dip the end of the wire in concentrated hydrochloric acid and heat it in a bunsen flame to clean it
2) Put the wire into the solid/compound
3) Hold the wire in the flame to see what colour is produced
When a few drops of sodium hydroxide are added, which metals produce a white precipitate?
Aluminium, calcium and magnesium
When a few drops of sodium hydroxide are added, what colour precipitate does iron (II) produce?
A green precipitate
When a few drops of sodium hydroxide are added, what colour precipitate does iron (III) produce?
A brown precipitate
When a few drops of sodium hydroxide are added, what colour precipitate does copper produce?
A blue precipitate
What metal produces a precipitate that then dissolves if sodium hydroxide is added in excess?
Aluminium
How would you produce ammonia?
By adding sodium hydroxide and warming the solution gently; the ammonium ions should produce ammonia
How would you test for ammonia / tell if it’s present?
It has a very strong smell however is colourless
It would also turn damp litmus paper blue
How would you test for a carbonate?
Any carbonate will produce CO2 when a dilute acid is added and then you would use the limewater test
What is the word equation for the limewater test?
Calcium hydroxide + carbon dioxide → calcium carbonate + water
Why does the limewater turn from clear to cloudy when CO2 is present?
Because calcium carbonate is produced which is a solid, turning it cloudy
How do you test for a halide ion?
You add silver nitrate solution (with dilute nitric acid) to a sample of the halide
What precipitate is formed when silver nitrate solution is added to chlorine?
A white precipitate of silver chloride
What precipitate is formed when silver nitrate solution is added to bromine?
A cream precipitate of silver bromide
What precipitate is formed when silver nitrate solution is added to iodine?
A yellow precipitate of silver iodide
How do you test for sulphates?
You add hydrochloric acid and barium chloride solution, a white precipitate of barium sulphate will form if the sulphate is present
What are some examples of instrumental analysis?
Mass spectrometry
Flame emission spectroscopy
Gas chromatography
What are the pros and cons of instrumental analysis?
Pros-
Uses smaller samples
Fast
Accurate
Gives a lot of information
Cons-
Machines / instruments can be expensive
What are the pros and cons of chemical analysis?
Pros-
Often simple to do
Cons-
It uses up the sample
What is flame emission spectroscopy used for and how is it better than a flame test?
To identify different ions in mixtures; this makes it more useful than flame tests which only work for substances that contain a single metal ion
How does flame emission spectroscopy work?
By measuring the specific wavelength of the light emitted by each ion
What is a formulation?
A mixture of different substances that forms a useful product
What is each part of a formulation called?
A component
