Acids, Alkalis and Salts

pH 0-3 = Red pH 4-6 = Yellow pH 7 (neutral) = Green pH 8-10 = Blue pH 11-14 = Purple

Colour in Acid: Red Colour in Netral: Red Colour in Alkali: Blue

Colour in Acid: Red Colour in Netral: Blue Colour in Alkali: Blue

Colour in Acid: Red Colour in Neutral: Yellow Colour in Alkali: Yellow

Colour in Acid: Colourless Colour in Neutral: Colourless Colour in Alkali: Pink

To measure the approximate pH value of a solution. Universal Indicator is better for pH value because it can measure across the full pH scale and has colour change depending on the acidity of the sample; but methyl orange is red in all acidic solutions, regardless of how acidic the solution is.

A: Red. The hydrogen atoms in hydrogen bromide dissociate in water to form H+ ions, which give the solution its acidity, thus forming hydrobromic acid.

A: Blue. Hydrogen bromide does not dissociate in organic solvents to form H+ ions, so the solution is not acidic, and no acid is formed.

- Acids are sources of hydrogen ions - H+ - Alkalis are sources of hydroxide ions - OH-

Hydrochloric acid + sodium hydroxide --> sodium chloride + water (neutralisation).

Sulphuric acid + copper oxide --> copper sulphate + water (neutralisation).

Nitric acid + sodium carbonate --> sodium nitrate + H20 + CO2

Hydrochloric acid + magnesium --> magnesium chloride + hydrogen

1) All nitrates are soluble 2) All chlorides are soluble, except silver chloride 3) All sulphates are soluble, except barium and calcium sulphate 4) All sodium, potassium and ammonium salts are soluble 5) All carbonates are Insoluble except sodium, potassium and ammonium carbonate. 6) All group 1 metals are soluble (all alkali metals - all dissolve in water to form alkalis!)

1) Add acid to excess metal/oxide/carbonate - by using excess of the metal, you ensure that their is no acid left in the solution after the react, so the filtrate will be a pure solution of salt. 2) Stir. 3) Filter to remove excess solid. 4) Gently heat to evaporate the water to saturation point. 5) Dry the crystals with a paper towel/oven

1) Add sodium salt solution of the anion to the nitrate solution of the cation until no more precipitate forms. 2) Filter to collect residue. 3) Wash the filter paper with distilled water. 4) Leave residue to dry on filter paper.

A: NaCl + AgNO3 ---> AgCl + NaNO3 1) Add dilute sodium chloride (chloride is the anion) to dilute silver nitrate (silver is the cation) solution until no more precipitate forms. 2) Filter. 3) Wash residue with distilled water. 4) Dry on windowsill/oven.

Titrations allow you to find out exactly how much acid is needed to neutralise a quantity of alkali (or vice versa).

1) Using a pipette, add some alkali (25cm cubed) to a conical flask along with two or three drops of indicator. 2) Fill a burette with the acid - DO IT BELOW EYE LEVEL, WHAT IF THE ACID SPILLS OVER? 3) Using the burette, add the acid to the alkali a bit at a time - whilst giving the conical flask the regular swirl. 5) The indicator will change colour when all the alkali has been neutralised. At this point stop adding the acid to the alkali. 6) Record the volume of acid used to neutralise the alkali. Repeat a few time for more reliable results.

Titration must be used. First you carry out normal titration, and find out the exact amount of acid needed to neutralise the alkali. Then you repeat it WITHOUT an indicator so that the salt is not contaminated with its colour. You remove the salt from the neutralised solution by evaporation, then you dry it.