Chemical Analysis

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Purity and Formulations

Usually pure means that nothing has been added to a substance

In chemistry, a pure substance is something that only contains one compound or element throughout

A chemically pure substance will melt or boil at a specific temp

Can test purity by measuring melting/boiling point and compare it with that of a pure substance

Closer the measured value is to the actual melting/boiling point, purer sample is

Impurities will lower melting point and increase melting range

Will also increase boiling point and may result in a range of temps at which sample boils

Are useful mixtures with a precise purpose that are made by following a formula

Each component in a formulation is present in a measured quantity

Contributes to properties of formulation so that it meets required function

Formulations are really important in pharmaceutical industry

By altering formulation, chemists can make sure it delivers the drug to the correct part of the body at the right concentration

So that it's consumable and has a long enough shelf life

Formulations can be found in cleaning products, fuels, cosmetics, fertilisers, metal alloys and even food/drink

When you buy a product, you might find that it has information about composition on the packaging

Allows to pick a formulation with right composition for a use

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Paper Chromatography

Analytical method to separate substances in a mixture

Can identify substances

Two phases of chromatography:

Mobile phase - where molecules can move. Always liquid or gas

Stationary phase - where molecules can't move. Can be solid or thick liquid

During chromatography experiment, substances in sample constantly move between mobile and stationary phases

An equilibrium is formed between two phases

Mobile phase moves through stationary phase, and anything dissolved in mobile phase moves with it

How quickly chemical moves depends on how it's distributed between the two phases - whether it spends more time in mobile phase or stationary phase

Chemicals that spend more time in mobile phase than stationary phase will move further through stationary phase

Components in a mixture will normally separate through stationary phase, so long as all components spend different time in mobile phase

Number of spots may change in different solvents as distribution of the chemical will change depending on solvent

Pure substance will only ever form one spot in any solvent as there's only one substance in sample

During paper chromatography, stationary phase is chromatography paper and mobile phase is solvent:

Amount of time molecules spend in each phase depends on two things:

How soluble they are in the solvent

How attracted they are to the paper

Molecules with a higher solubility in solvent, and which are less attracted to paper, will spend more time in the mobile phase

Carried further up the paper

Result of chromatography analysis is called a chromatogram

Retention factor is ratio between distance travelled by dissolved substance and distance travelled by solvent

Further through stationary phase a substance moves, the larger the retention factor

Rf= distance travelled by substance/distance travelled by solvent

Chromatography is often carried out to see if a certain substance is present in a mixture

Run a pure sample of that substance alongside unknown mixture

If retention factor values of reference and one of the spots in the mixture match, the substance may be present

Retention factor is dependent on the solvent

If you change the solvent the Rf value for a substance will change

Can test both mixture and reference in a number of different solvenst

Page 3

Tests for Gases

Chlorine

Bleaches damp litmus paper, turning it white

May turn red for a moment - because solution of chlorine is acidic

Oxygen

If you put a glowing splint inside a test tube containing oxygen, splint will relight

Carbon Dioxide

Bubbling carbon dioxide through (or shaking Co2 with) an aqueous solution of calcium hydroxide (limewater) causes solution to turn cloudy

Hydrogen

If you hold a lit splint at the open end of a tst tube containing hydrogen, you'll get a squeaky pop

Noise comes from hydrogen burning quickly with oxygen in the air to form H2O