Chemistry - pure substance - only contains 1 compound or element throughout.
Chemically pure susbstance - melts or boils at specific temp. Can test purity of sample by measuring melting or boiling point & comparing it with melting or boiling point of pure substance. Closer measured value is to actual melting or boiling point, the purer sample is. Impurities in sample will lower melting point & increase melting range of substance. Will also increrase boiling point and boiling range.
Formulations - useful mixtures with precise purpose made by following 'formula'. Each component in formulation is present in measured quantity, & contributes to properties of formulation so it meets its required function. Important in pharmaceutical industry - e.g. by altering formulation of pill, chemists can ensure it delivers drug to right part of body at right concentration, that its consumable & have long enough shelf life. Everyday life - cleaning products, fuels, cosmetics, etc. When buying product, it has information about its composition on packaging - shows product's a formulation.
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Paper Chromatography
Two 'phases' - mobile = where molecules can move - liquid or gas. Stationary = where molecules can't move - solid or really thick liquid. During chromatography experiment, substances in sample always move between the 2 phases - equilibrium formed. Mobile phase moves through stationary phase & anything dissolved in mobile phase moves with it.
How quickly chemical moves depends on how it's 'distributed' between the 2 phases - chemicals that spend more time in mobile phase move further through stationary phase.
Components in mixture will normally separate through stationary phase if all components spend different amounts of time in mobile phase. Number of spots may change in different solvents as distribution of chemical changes depending on solvent. Pure substance will only ever form 1 spot in any solvent - only 1 substance in sample.
Stationary phase - chromatography paper & mobile phase - solvent. Amount of time molecules spend in each phase depends on how soluble they are in solvent, & how attracted they're to paper. Molecules withe higher solubility in solvent, & less attracted to paper will spend more time in mobile phase - carried further up paper.
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Tests for Gases
Chlorine bleachesdamp litmus paper white. May turn red for moment as solution of chlorine is acidic.
If you put glowing splint in test tube with oxygen, oxygen will relight splint.
Bubbling carbondioxide through, or shaking carbon dioxide with an aqueous solution of calcium hydroxide - limewater - causes solution to go cloudy.
If you hold lit splint at open end of test tube containing hydrogen, you'll get 'squeaky pop'. Noise comes from hydrogen burning quickly with oxygen in air to form H2O
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