C8 - Chemical Analysis

Define mixture

Two or more elements or compounds that are not chemically bonded

Define pure

A single substance containing either only one element or one compound

Define impure

More than one element or compound

How do you identify a pure substance?

It has fixed melting and boiling points

Define formulation

A mixture that has been designed as a useful product, made by mixing components in carefully measured quantities to give the products the best properties for its use

What are formulations found in?

Cleaning products, fuels, cosmetics, fertilisers

What are the two phases of chromatography?

Mobile and stationary

What is the mobile phase?

Where molecules can move (always liquid or gas)

What is the stationary phase?

Where the molecules can't move (always a solid or a thick liquid)

What will move further - chemicals that spend longer in the mobile or stationary phase?

Mobile

What is the stationary phase in paper chromatography?

The chromatography paper

What is the mobile phase in paper chromatography?

The solvent (water or ethanol)

What decides how long molecules spend in each phase of chromatography?

Their solubility in the solvent and how attracted they are to the paper

What are Rf values?

Ratio between the distance travelled by the dye (solute) and the distance travelled by the solvent

Rf=

Distance travelled by substance / distance travelled by solvent

The larger the Rf value...

the more soluble it is

What should the Rf value be under?

1

What is the test for oxygen gas?

Glowing splint relights

What is the test for carbon dioxide?

Limewater (CaCO3) turns cloudy

What is the test for hydrogen gas?

Lit splint makes a "squeaky pop" sound

What is the test for chlorine gas?

Damp litmus paper turns white/bleached

What is limewater

Calcium hydroxide

What is used to carry out a flame test for positive metal ions?

Looped nichrome wire

What colour flame shows the presence of the positive ion sodium?

Yellow

What colour flame shows the presence of the positive ion potassium?

Lilac

What colour flame shows the presence of the positive ion calcium?

orange-yellow

What colour flame shows the presence of the positive ion copper?

Green

What colour flame shows the presence of the positive ion lithium?

Crimson

What will form in the hydroxide test for positive ion Calcium?

White precipitate

What will form in the hydroxide test for positive ion Copper (2)?

Blue precipitate

What will form in the hydroxide test for positive ion Iron (2)?

Green precipitate

What will form in the hydroxide test for positive ion Iron (3)?

Brown precipitate

What will form in the hydroxide test for positive ion Aluminium?

White and then colourless precipitate

What will form in the hydroxide test for positive ion Magnesium?

White precipitate

What is a precipitate?

a solid that forms and settles out of a liquid mixture

What are the issues associated with carrying out a flame test?

Colours can mask each other or mix and look like another colour

What is the test and observation for the negative ion Carbonate?

Add an acid to react and produce CO2, use cloudy limewater to test for CO2

What is the test and observation for the negative ion Sulphate?

Add either barium chloride or barium nitrate, forms a white precipitate

What is the test and observation for the negative ion Chloride?

Add silver nitrate, forms a white precipitate

What is the test and observation for the negative ion Bromide?

Add silver nitrate, forms a cream precipitate

What is the test and observation for the negative ion Iodide?

Add silver nitrate, forms a yellow precipitate

Why are instrumental methods used?

More accurate, sensitive and rapid

What is flame emission spectroscopy?

An instrumental analysis tool for identifying metal ions

How does flame emission spectroscopy work?

Sample placed in a flame, electron is excited down a level, emits a wavelength of light that is picked up by a photographic plate or computer

How does the Rf value allow you to identify a substance?

Each solvent has a different Rf value

What does the intensity of the spectrum indicate?

The concentration of that ion in solution

What shows a positive result for a lithium metal ion?

Crimson flame

What shows a positive result for a sodium metal ion?

Yellow flame

What shows a positive result for a potassium metal ion?

Lilac flame

What shows a positive result for a calcium metal ion?

Orange-red flame

What shows a positive result for a copper (2) metal ion? (there are two methods)

Green flame,

Copper hydroxide = blue precipitate

What shows a positive result for an iron (2) metal ion?

Iron (2) hydroxide = green precipitate

What shows a positive result for an iron (3) metal ion?

Iron (3) hydroxide = brown precipitate

What colour is the precipitate of calcium hydroxide?

White

What colour is the precipitate of magnesium hydroxide?

White

What colour is the precipitate of aluminium hydroxide?

White (dissolves)

What do you react a metal ion with to get a precipitate?

Sodium hydroxide

Which white hydroxide dissolves in excess sodium hydroxide?

aluminium

What do you react halide ions with to test them?

silver nitrate

In the sodium hydroxide test for cations, which two ions give a white precipitate?

Calcium and magnesium (aluminium dissolves)

When testing for halide ions, is nitric acid or hydrochloric acid used?

nitric acid

Which is the stationary phase in paper chromatography?

the paper