Topic 3a -Acids Bases and Salts

Making salts

Soluble salts

1) Gently heat sulfuric acid in a water bath

2) Add copper oxide and sir until it is in excess

3) This shows the acid is neutralised and the reaction is finished

4) Filter out the excess coppper oxide from the copper sulphate to make sure there is no contamination

5) After filtration, crystalize the copper sulphater solution by evapouration

6) Once salt starts to form, stop heating and leave to cystalize, it is now a pure soluble salt

Making copper sulphate

Insoluble salts

1) Mix two solutions together, lead nitrate and sodium cholride, a salt will form as a precipitate

2) Set up a filtration process

3) Pour the solution through the funnel

4) Once any excess water is drained, wash the salt (lead chloride) using distilled water

5) Leave the salt out to dry

Acids

Weak Acids

Only partially dissociate in water, only some of the molecles realease H+ ions

Carboxylic acids are weak acids, like citric and carbonic acids

Weak acids tend to have a pH of around 2-6

Ionisation of a weak acid is reversible

Strong acids

Almost completely dissociate in water

When acids are added to an aqueous solution, they ionise, the strength of an acid tells you about the proportion of acid particles that will dissociate

Sulfuric acid and nitric acid

Acid strength

An acid with a high volume of water compared to the acid is dilute

The more grams of acid per dm3, the more concentrated

A concentrated solution has a greater amount of dissolved solute particles than a dilute solution

Acid strength tells you the proportion of water to acid molecules

pH indicators

Methyl orange

Red in acid

Peach in neutral

Yellow in alkaline

Litmus

Red in acid

Blue in alkaline

purple in neutral

Phenolphthalein

colourless in acid

colourless in neutral

bright pink in alkaline

Reactions

Neutralisation reactions

H+(aq) + OH-(aq) --> H20(l)

Solution formed in neutral

At pH 7, the concentration of OH- ions equals the concentration of H+ ions

Acid + Base --> Salt + Water

Reactions with metals

Acid + Metal --> metal salt + hydrogen

Reactions of acids

Acid + Metal hydroxide --> Salt + Water

Reactions with metal carbonates

Acid + Metal carbonate --> Metal Salt + CO2 + H2O

Solubility rules

Carbonates

Soluble = Ammonium, Potassium, Sodium Carbonate

Insoluble = All others

Hydroxides

Soluble = Ammonium, Potassium, Sodium Hydroxide

Insoluble = All others

Chlorides

Insoluble = Lead and Silver Chloride

Soluble = All others

Sulphates

Insoluble = Barium, Calcium, Lead Sulphate

Soluble = All others

Nitrates

All Soluble

Tests

Test of CO2

Limewater test

Bubble the gas through limewater

If it turns cloudy, then CO2 is present

Caused by Calcium carbonate forming

Test for Hydrogen

Squeaky pop test

Light a splint and put it at the open end of a test tube

If you hear a squeaky pop, then there is hydrogen present

Noise comes from hydrogen burning in the air with the oxygen

Concentration and pH

Concentration meansures how much acid there is in a litre of water

If the concentration of H+ ions decreases by X10, the pH decreases by 1

Source of hydrogen ions .

Base

Any substance than reacts with an acid to from salt and water only

Metal hydroxides and metal oxides

Metal carbonates react with acids to produce a salt, water and carbon dioxide only

Metals react with acids to produce a salt and hydrogen only

pH of 0-2

Higher concentration of H+ ions than a weak acid

You can change the concentrated solution into a dilute solution by adding more water to it

You can change a dilute solution into a concentrated solution by dissolving more solute in it or evapourating some of the water

Method

Add some dilute HCl into the beaker

Measure and record the pH of the contents of the beaker

Add a small madd of calcium hydroxide powder, stir and then measure and record the pH again

Repeat until the pH no longer changes

Concentration

When an acid is in solution, a higher concentration of H+ ions means the solution is more acidic, thus having a lower pH

When an alkali is in solution, a higher concentration of OH- ions means that the solution is more alkaline, thus having a higher pH

Concentrated = larger amount of substance in a given volume

Dilute = less amount of substrance in a given volume

We add excess to ensure the acid reacts completely

The remaining solution is salt and water only because the acid has fully reacted and the other product has been filtered

We filter out the excess reactant so that you are left with just salt and water