Chemical analysis

A chemically pure substance is a single element or comound, such as water, glucose, copper sulphate. Purity is worked out by looking at the melting or boiling points of samples.

Pure samples have exact and specific melting and boiling points, the closer the values of the sample the greater the purity of the sample.

Impurities lower the melting point and widen the range of temperatures at which the sample will melt.

Impurities will increase the boiling point and widen the range of temperatures at which the sample will boil.

Formulations are mixtures of chemicals that have been designed to create useful products. 

In a formulation each component helps to decide what the mixture's overall porperties are.

To make sure that a formulation does what it's supposed to, each chemical component must be present in a precisely measured quantity.

Some examples of formulations are Fuel, Metal alloys, fertilisers and medicines.

Chromatography is a process that seperates a mixture into its different components.

Substances are picked up and carried by a mobile phase (liquid or gas). The mobile phasse then moves through a stationary phase (solid or viscous liquid)

A substance moves far if it's attracted more to the mobile phase and it won't move far if it's more attracted to the stationary phase.

Differrent components can sometimes be equally attracted to a solvent. So, the number of spots a mixture produces can vary depending on the solvent used.

Rf values = distance travelled by substance/ distance travelled by solvent

Testing for Hydrogen: Place  lit splint close ot the mouth of a test tube that contains a gas, if it makes a squeaky pop sound it's hydrogen.

Testing for Oxygen: Place a glowing splint in a test tube that contains a gas, it will relight if oxygen is present.

Testing for Carbon Dioxide: Take an aqueous solution of limewater and bubble the gas through. If carbon dioxide is present the limewater will turn from clear to cloudy.

Testing for Chlorine: Insert damp litmus paper into a test tube, if chlorine is present the litmus paper will  bleach and turn from coloured to white.

Some metal ions can be identified using flame tests. The following positive metal ions all produce a characteristic flam colour when burned:

Calcium (Ca2+) - Orange/red; Sodium (Na+) - Yellow; Copper (Cu2+) - Green, Lithium (Li+) - Crimson; Potassium (K+) - Lilac

Submerge a nichrome wire loop in dilute hydrochloric acid to make sure that it's clean. Place the wire loop into the sample to be tested and hold it in the bunsen's roaring blue flame. Observe any colour change.

Testing for Carbonates - A reaction between a carbonate and dilute acid gives a salt, carbon dioxide and water. As carbon dioxide is produced we can use the standard corban dioxide test to work out if the unknown substance is a carbonate.

Testing for Halides - Add nitric acid to an unknown solution, this removes carbonate ions whcih could disrupt test results by forming a precipitate with the silver nitrate. Then add silver nitrate, if  halide ions are present they will form a precipitate with the silver ions. (AgBr is cream, AGI is pale yellow)

Testing for Sulfates - Add dilute hydrochloric acid, this removes carbonate ions. Then add barium chloride, if sulfates are present the white precipitate barium sulfate will form.

Modern technology provides us with very accurate instruments. These instrumental methods have advantages and disadvantages compared to traditional methods. 

Advantages - Greater sensitivity and accuracy, quicker, able to analyse tiny samples

Disadvantages - Often expensive, need special training, results are only useful when compared to data from known substances.

Examples, Flame Emission Spectroscopy to identify metal ions