Chemical analysis

What is chemical analysis

The instruments and methods we use to separate, identify and quantify different substances

What’s a pure substance

Single element or compound that hasn’t been mixed with any other substances

• they always melt and boil at specific temperatures

What’s an example of pure substances

Distilled water

If given specific freezing and boiling points of a substance, how can you test to see if they are true

• Boil the water and see if it boils at given temperature

• Freeze it and see if it the frisking point is the given temperature

• If it doesn’t get the results of the given democrats the substance is impure

What are formulations

Mixtures that have been prepared using a specific formula

• formulations are made from precise amounts of different components, and each component has a different function

• To make paints, cleaning agents and medicines, they all require formulations

What techniques can you use to separate the substances

• Filtration,

• distillation,

• Chromatography

• Crystallisation

If we test a substance for purity by measuring its boiling point, is that a physical or chemical test

Physical

What is chromatography

A chemical analysis technique used to separate substances in a mixture

What is paper chromatography used for

To separate a mixture of soluble substances in a liquid

What’s the name given to the pencil lime in chromatography and why do we use pencil

• The baseline

• Use pencil as pen ink would dissolve and move up the paper

• It should not be submerged in solvent

What’s the name of the resulting paper we end up with

A chromatogram

What’s the mobile phase in chromatography

• refers to the molecules that can move

• The solvent

What happens to a substance that is more soluble in chromatography

• will spend more time in the mobile phase

• This means it will move faster and travel a further distance up the paper

What’s the stationary phase in chromatography

• refers to particles that can’t move

• The paper

What happens to a substance less soluble in chromatography

• will spend more time in the stationary phase

• So it moves slower and not travel very far up the paper

How do you calculate the Rf value

Distance travelled by substance / distance travelled by solvent

What happens if you change the stationary and mobile phase when working out art value

• specific to each phase so will get a different Rf value

How do you test for chlorine gas

• Test: expose it to damp blue litmus paper

• Results: The litmus paper will turn red then bleached white

• Safety precautions:

  • wear gas mask

  • Do experiment in fume cupboard

How do you test for oxygen gas

• test: expose it to a glowing splint

• Result: the glowing splint will relight

• Safety precautions:

  • eye protection

How do you test for hydrogen gas

• test: expose it to a lot splint

• Result: squeaky pop sound

• Safety precautions:

  • eye protection

How do you test for carbon dioxide gas

• test: bubble it through lime water

• Results: lime water turns cloudy

• Safety precautions:

  • eye protection

How do you test for carbonate ions ( test for anions)

• React the substance with hydrochloride acid

• If the substance contains a carbonate ion, carbon dioxide gas will bubble out of the solution

• Collect the gas and bubble it through lime water

• If the lime water turns cloudy, it confirms the gas is carbon dioxide

• Confirmation that the gas is carbon dioxide is confirmation that the original substance contained carbonate ions

If a chemical reaction is taking place in a test tube, what methods can be used to collect the

• place an upside down measuring cylinder over the test tube to trap had

• Attach the top of a test tube to a gas syringe

How do you test for sulfate ions ( test for anions )

• react the substance with hydrochloride acid to remove any carbonate ions

• Add barium chloride solution

• If sukfste ions are present, it will form a white precipitate of barium sulfate

Why do we have to add hydrochloride acid first when testing for sulfate ions

• to remove any carbonate ion impurities

How do we test for halide ions ( test for anions )

• react the solution with nitric acid to remove any carbonate ions or sulfate ions

• Add silver nitrate solution

• If a white precipitate forms, the substance contains chloride ions

• If a cream precipitate forms the substance contains bromide ions

• If a yellow precipitate forms the substance contains iodide ions

When testing for halide ions why must we react nitric acid

You can’t use hydrochloric acid as that would introduce chloride ions which could then react with the silver ions

What are the two groups of tests for cations

• flame tests

• Metal hydroxide tests

How do you prepare for a flame test

1. Take a platinum (or nichrome) wire loop, clean it by dipping it in some dilute hydrochloric acid, rinsing it n distilled water, and then heating it over a Bunsen burner flame

2. Duo the wire loop into the compound you want to test

3. Hold the wire loop in the clear blue part of the Bunsen burner flame (this is the hottest part)

4. See shot colour the flame turns as the compound burns

What is used to clean the platinum wire loop

• hydrochloric acid

• Bunsen burner flame

What colour is each metals flame

• lithium ions = crimson flame

• Sodium ions = yellow flame

• Potassium ions = lilac flame

• Calcium ions = orange - red flame

• copper ions = green flame

What’s the limitations of the flame test

If you have 2 or more different method in your sample, the colours of the flames will mix together sniff you will have to judge or won’t teak what you have → less reliable