Acids, bases and salts

Chemistry - acids,bases and salts

• Phenolphthalein Indicator
• in acid - colourless
• Neutral solution - colourless
• in alkaline solution - pink
• Methyl orange
• in acid - red
• in neutral solution - orange
• in alkaline solution - yellow
• red litmus paper
• in acid - red
• in neutral solution - red
• in alkaline solution - blue
• Blue litmus paper
• in acid - red
• in neutral solution - blue
• in alkaline solution - blue
• Validity- how valid the experiment is
• reliability- will you get the same result if you were to repeat the experiment
• accuracy- is the value obtained from the measurement close to the correct value
• Strong acid will fully ionise in water.
• Weak acid will only partially ionise.
• hydrochloric acid HCL
• sulfuric acid H2So4
• Ethanoic acid Ch3COOH
• nitric acid. HNO3
• neutralisation is the reaction between an acid and an alkali producing a salt and water .
• A salt is a compound formed when some or all of the hydrogen ions in an acid are replaced by metal or ammonium ions
• Metal + acid = salt + hydrogen
• Eg. Magnesium + hydrochloride acid = magnesium chloride + hydrogen

Acids bases and salts

• Hydrogen test - lit splint pop test
• Apply a lit splint to top of test tube - if hydrogen is present it will pop and hydrogen burns explosively in air and reacts with oxygen to produce water.
• 2H2 + O2 = 2H2O
• Metal oxide + acid = salt + water
• metal hydroxide + acid = salt + water
• metal carbonate + acid = salt + carbon dioxide+water
• ammonia + acid = ammonium salt
• Test for carbon dioxide
• limewater changed from colourless to milky.
• Observations during acid reactions
• •exothermic
• •solid will disappear
• • bubbles of gas produced

Salt preparation

• Method 1 - Titration
• used for making all sodium and potassium salts
• carried out using a pipette to measure the exact volume of one solution and the other solution is added using a burette.
• prep: Pipette 25cm3 of the alkali into a conical flask and add a few drops of phenolphthalein indicator, which gives it a pink colour. Fill the burette to mark with acid and run into comical flask until colour change s to colourless. Record volume of acid used and repeat without indicator to get a solution that only contains salt. Instead of repeating without indicator, indicator can be removed by adding charcoal, heating and filtering the solution.
• Purification : heat solution until volume is half and leave it to cool and crystallise. Filter of crystals between two sheets of filter paper, in a low temperature oven or a desiccator.
• Method 2- using an insoluble solid
• Uses a base or a carbonate, using a metal carbonate has an advantage as it produced CO2, so when all of acid has been neutralised no more bubbles are produced.
• Solid used is added bit by bit to acid and will eventually be in excess.
• prep: Add excess of insoluble solid to 25cm3 of an acid in conical flask, heat and stir to make sure there is some unreacted solid left. Filter off the insoluble solid (residue) and pour the filtered liquid (filtrate) into an evaporating basin.
• Purify the filtrate the same as method 1.
• Purification : heat solution until volume is half and leave it to cool and crystallise. Filter of crystals between two sheets of filter paper, in a low temperature oven or a desiccator.