SC9: Qualatative Analysis

Explain why the test for any ion must be unique

You would never be able to know which specific ion it was if more than one ion gave the same result. Metal ions produce a **colour** if heated strongly in a flames. Ions from **different** metals produce **different** **colours**

How do you conduct a flame test?

Dip the loop of an **unreactive** metal wire such as nichrome or platinum in dilute acid, and then hold it in the blue flame of a Bunsen burner until there is no colour change. This cleans the wire loop and avoids **contamination.** This is an important step as the test will only work if there is just **one type** of ion present. Two or more ions mean the colours will mix, making identification erroneous. Dip the loop into the solid sample and place it on the edge of the **blue** Bunsen flame. Avoid letting the wire get so hot that it glows red otherwise this can be confused with a flame colour

Flame test colours

Lithium (Li+) Red

Sodium (Na+) Yellow

Potassium (K+) Lilac

Calcium (Ca2+) Orange-red

Copper (Cu2+) Blue-green

Describe the chemical test for ammonia

Makes damp red litmus paper turn blue

* It also forms a white smoke of ammonium chloride when hydrogen chloride gas, from concentrated hydrochloric acid, is held near it

Describe tests to identify a carbonate ion in solids or solutions

Add hydrochloric acid, bubble the gas produced through limewater \n

* limewater turns cloudy if carbonate present

Describe tests to identify the sulfate ion in solids or solutions

Using dilute hydrochloric acid and barium chloride solution

* Add dilute HCl followed by barium chloride solution ○A white precipitate will form when sulfate ions are in this solution

Describe tests to identify the halide ion in solids or solutions

* First add dilute nitric acid, followed by silver nitrate solution
* Chloride gives a white precipitate
* Bromide gives a cream precipitate
* Iodine gives a yellow precipitate

Describe the colour produced from tests to identify aluminium, calcium, copper, iron 1 and 2 in the hydroxide test

Aluminium (Al3+) White, dissolves in excess NaOH(aq)

Calcium (Ca2+) White, no change in excess NaOH(aq)

Copper (Cu2+) Blue

Iron(II) (Fe2+) Green

Iron(III) (Fe3+) Brown

What are the instrumental methods and what is there purpose?

* Elements and compounds can be detected and identified using instrumental methods oThese are accurate, sensitive and rapid
* Instrumental methods include: gas chromatography and mass spectrometry

Describe flame photometer, to​ ​determine​ ​the concentration​ ​of​ ​ions​ ​in​ ​dilute​ ​solution​ ​using​ ​a​ ​calibration​ ​curve,​ ​and​ ​to identify​ ​metal​ ​ions​?

* Example of an instrumental method used to analyse metal ions in solutions
* Sample is put into a flame and the light given out is passed through a photometer
* Output is a line spectrum that can be analysed to identify the metal ions in the solution and measure their concentrations

Describe the hydroxide test and what to do if a precipitate that is white forms.

1. Place a little of the unknown solution in a test tube and add a few drops of dilute sodium hydroxide solution. Record any observations.
2. If white precipitate forms, add an excess of sodium hydroxide solution and record any observations.

What is the size of a nano particle compared to a normal atom?

* Nanoparticles are 1-100 nanometers across.
* They contain a few hundred atoms.
* Nanoparticles, are smaller than fine particles, which have diameters between 100 and 2500 nm (1 x 10-7 m and 2.5 x 10-6 m).
* As the side of cube decreases by a factor of 10 the surface area to volume ratio increases by a factor of 10

Why are nanoparticles used?

* Nanoparticles involve fullerenes.
* A nanoparticle has different properties to the ‘bulk’ chemical it’s made from, because of their high surface area to volume ratio.
* It may also mean that smaller quantities are needed to be effective than for materials with normal particle sizes.

Uses of nanoparticles

* High S:V ratio → good catalysts.


* Produce highly selective sensors.
* Nanotubes could make stronger, lighter building materials.
* New cosmetics, e.g sun tan cream and deodorant. They make no white marks.
* Lubricant coatings, as they reduce friction. These can be used for artificial joints and gears.
* Nanotubes conduct electricity → small electrical circuits

What are the risks associated with nanoparticle materials?

* may enter blood stream
* effects of nanoparticulate materials are unknown so its hard to assess risks of using it

What are the physical similarities and differences of glass and clay ceramics, polymers, composites and metals

* glass ceramics: transparent, hard, brittle, poor heat and electrical conductors
* clay ceramics: opaque, hard, brittle, poor heat and electrical conductors
* polymers: can be made transparent/ translucent/ opaque, poor heat and electrical conductors, can be tough or ductile
* metals: shiny, good heat and electrical conductors, hard, tough