acids and alkalis

indicators

universal indicator : add indicator to solution being tested, compare colour against pH scale

litmus paper: put in solution, red in acidic, blue in alkaline, purple in neutral

phenolphthalein: clear colourless in acidic and pink in alkaline

methyl orange: red in acidic, orange in neutral, yellow in alkaline

acids can be neutralised by bases

• an ACID is a source of hydrogen ions (H+)

they are proton donors

have a pH of less than 7

• a BASE is a substance that can neutralise an acid.

they are proton acceptors

• ALKALIS are soluble bases

an alkali is a source hydroxide ions (OH-)

ph greater than 7

• neutralisation : H+ (aq) + OH- (aq) -> H2O (l)

acid donates proton which is then accepted by the base

acid + base →

salt + water

acid + metal oxide

salt + water

acid + metal hydroxide

salt + water

acid + ammonia

ammonium salt

acid + metal carbonate

salt + water + carbon dioxide

acid + metal

salt + hydrogen

solubility rules :

common salts of sodium, potassium and ammonium (spa)

all soluble

solubility rules :

nitrates

all soluble

solubility rules :

common chlorides

soluble, except silver chloride and lead chloride

common sulfates

soluble, except lead, barium and calcium sulfate

common carbonates

insoluble, except SPA salts

common hydroxides

insoluble, except for SPA and calcium ones

making insoluble salts: precipitation reactions

react 2 soluble salts e.g. lead nitrate + magnesium sulfate = lead sulfate + magnesium nitrate

• add 1 spatula lead nitrate to test tube and dissolve with distilled water. stir thoroughly to ensure all dissolved. repeat in separate test tube with 1 spatula magnesium sulfate.

• pour the 2 solutions into a beaker, stir. lead sulfate will precipitate out.

• filter the contents of the beaker using a funnel, piece of filter paper and beaker, collecting the residue

• swill out the beaker with more distilled water and filter it to obtain all precipitate

• rinse contents of filter paper -> all soluble magnesium nitrate washed away

• scrape lead sulfate onto fresh filter paper , leave to dry in warm oven

make soluble salt - acid and insoluble base

• heat acid in water bath - speeds up reaction. do in fume cupboard so no acid fumes.

• add base to acid , will react to produce soluble salt and water. add base in excess so no leftover acid in your product.

• filter off excess solid to get solution with only salt and water

• gently heat solution, with Bunsen burner, slowly evaporate some water

• leave solution to cool, allow salt to crystallise

• filter off solid salt and leave to dry in warm oven

EG ADD COPPER OXIDE TO WARM SULFURIC ACID to make copper sulfate solution and then hydrated copper sulfate crystals

make soluble salt using titration

react acid with alkali, but u can't see when reaction finished and don't want salt contaminated so can't add excess

• use pipette, measure set amount alkali into conical flask w/ pipette

• add a few drops indicator

• add acid to burette, note starting volume

• add acid slowly to alkali, using burette, until reach end point

• note and record final volume acid in burette, calc difference

• carry out reaction w exactly the same volumes of acid and alkali, no indicator so salt not contaminated w indicator

• solution remaining when reaction complete = only soluble salt and water

• slowly evaporate off some water and leave solution to crystallise. filter off solid and dry by leaving in warm oven

E.G. sodium chloride from HCl and NaOH