Qualitative analysis

qualitative analysis

• used to identify components in a sample

• use sampling techniques to ensure that samples used for analysis are representative

• will identify any variations in the bulk of the material that is represented in the analysis

flame test for metal ions

• light bunsen burner

• clean nichrome wire with HCl

• put nichrome wire in the flame to clean

• collect concentrated chemical solution on nichrome wire and place in flame

• record colour of flame

flame test barium

pale-green

flame test calcium

yellow-red

flame test copper

green-blue

flame test lithium

red

flame test sodium

orange

flame test potassium

lilac

Emission spectrum

• black background with coloured lines

• shows the frequency of light that an element will send out

How to identify an element on the emission spectrum

• look at emission spectrum and compare data

• if only some line match its not the element present

• if the lines match up but have extra lines there could be multiple elements

advantages of emission spectrum

• can detect very small amounts of a substance (greater sensitivity)

• greater accuracy

• greater speed

• can detect different elements in mixtures

Detecting cations

precipitation can be used to determine which ions are in a compound

precipitate

insoluble solid which forms when two solutions are mixed

How to detect cations in solution

1. add 10 drops of compound to a test tube

2. add a small volume of sodium hydroxide to compound until precipitate forms

3. record colour of precipitate

4. add more sodium hydroxide to see if the precipitate is soluble

5. record whether precipitate is insoluble/soluble

metal cations react with hydroxide ions

ion copper (cu2+)

precipitate colour = light blue

insoluble

ion iron (Fe2+)

precipitate colour= green

insoluble

ion iron (Fe3+)

precipitate colour = red-brown

insoluble

ion calcium (Ca2+)

precipitate colour = white

insoluble

zinc (Zn2+)

precipitate colour = white

soluble

Detecting anions in a solution

Acidify with dilute nitric acid then add silver nitrate solution

for Sulfate → acidify the add barium chloride/barium nitrate solution

for carbonate → add dilute acid and if bubbles form collect the gas and test with limewater

chloride

white precipitate

Bromide

cream precipitate

Iodide

yellow precipitate

Sulfate

white precipitate

Carbonate

effervescence Co2 gas