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Summary Notes for GCSE Chemistry Acid, Bases, Salts and Neutralisation
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Notes for GCSE Chemistry Acid, Bases, Salts and Neutralisation
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Taylor’s Notes Acids, Bases, Salts and NeutralisationIndicators
Indicator Colour in Acid Solution Colour in Alkaline Solution
Litmus Red Blue
Phenolphthalein Colourless Pink
Methyl Orange Orange Yellow
Acids
Acids are a source of hydrogen ions
Acid + Base Salt + Water
Acid + Metal Oxide Salt + Water
Acid + Metal Salt + Hydrogen
Acid + Metal Carbonate Salt + Water + Carbon dioxide
Bases
Bases are acceptors of H+ ions They can be insoluble (bases) or soluble (alkalis)
An alkali is a soluble bases and are a source of hydroxide ions, OH-
Solubility Rules
All common sodium, potassium and ammonium salts are soluble
All nitrates are soluble
Chlorides are soluble except silver chloride and lead chloride
Sulphates are soluble except barium, calcium and lead
Carbonates are insoluble except sodium, potassium and ammonium
Hydroxides are insoluble except sodium, potassium and ammonium, calcium is only slightly soluble
Salt Preparation by Excess Base
Excess base is used when an insoluble base reacts with an acid to form a soluble salt
1. Add base to an acid and stir and heat until excess base remains unreacted at the bottom of the beaker
2. Filter the mixture to remove the excess base as residue on the filter paper
3. Collect the filtrate in an evaporating basin
4. Perform a crystallization
Salt Preparation by Precipitation
Insoluble salts are prepared in precipitation reactions, using two soluble solutions to produce an insoluble salt. This is done by matching the
positive and negative ions in the starting materials.
Barium sulphate for example: Ba(NO3)2(aq) + Na2SO4(aq) → BaSO4(s) + 2 NaNO3(aq)
Precipitation is used when two solutions of soluble substances react to form an insoluble salt
1. Mix together two solutions of soluble substances
2. A precipitate of the insoluble salt forms
3. Filter the mixture and keep the residue
4. Wash the residue with distilled water
5. Allow the solid to dry in a warm place with no direct heating
Salt Preparation by Titration
A titration is used when two solutions of soluble substances react to form a soluble salt
1. Fill a burette with a chosen acid up to the 0.00 mark
2. Add 25.0 of alkali to a conical flask using a pipette
3. Add an appropriate indicator to the conical flask
4. Add acid drop by drop to the alkali whilst swirling until a colour change is observed
5. Repeat steps 1) to 4) until concordant results are obtained
6. Repeat steps 1) to 4) without indicator using the volume recorded and perform a
crystallisation
Universal Indicator isn’t used in a titration as it does not give a specific distinct colour change
Crystallisation
1. The salt solution is placed in an evaporating basin
2. The solution is heated until a saturated solution form
3. The solution is not heated to dryness to prevent the thermal decomposition of the salt formed
4. A solution is saturated when a cold glass rod dipped in forms crystals of the salt on the tip
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