Acids, bases and salts

acid

A hydrogen containing substance that when dissolved in water produces H+ ions

Base

An insoluble metal oxide which’s will neutralise an acid forming a salt

Alkali

A metal hydroxide which will dissolve in water forming OH- ions

Salt

A neutral ionic compound formed by the neutralisation of an acid

How to determine an acid/alkali

Litmus paper

Litmus paper results

Blue litmus turns red = acid

Red litmus turns = base/alkali

Neutral = no change

Universal indicator

Red = acidic, purple= alkaline, green=neutral

Determining the name of a salt

The name of the salt depends on the acid which was neutralised

• hydrochloric acid= chloride

• Sulfuric acid= sulfate

• Nitric acid= nitrate

Acid reactions with reactive metals

If the metal is more reactive than hydrogen, the metal will displace the hydrogen forming a salt

Eg. Magnesium + hydrochloric acid —> magnesium chloride + hydrogen

Acid reaction with bases

Acids react with bases to from salt and water

Acid Reaction with alkali

Acids react with alkalis to from a salt and water

Acids reaction with alkali: ionic equation

Acids contain dissovled hydroge ions and alkalis contain dissolved hydrogen ions

H+(aq) + OH-(aq) —> h20

Alkali reactions with metal carbonates

If an acid is added to a metal carbonate, such as limestone, you will see fizzing. This is because the gas, carbon dioxide is produced. The carbonate neutralises the acid to form a salt, water and carbon dioxide.

Carbonate test for acids

A carbonate like sodium chloride can be used to test for an acid, if you add it to an acid you will see fizzing. (Only fizzes if acid is present)

Observation of copper oxide

Black powder

Observation of copper carbonate

Green powder

Observation of copper sulfate solution

Blue, when the water evaporates, copper crystals are also blue

Acid-alkali titration method

1. Measure the volume of acid needed to neutralise the alkali using the titration

2. Repeat the titration without the indicator, adding the measured volume from step 1

3. Pour the solution into an evaporating basin and leave to evaporate slowly in a warm place

Acid-alkali detailed titration

1. 1st reading obtained from this experiment is a “rough” reading because you do not know exactly when the colour change will occur/“end point”

2. For the 2nd reading, run the solution through to just before the end point and then acid the acid drop by drop until the solution changes colour

3. Repeat the experiment multiple times and calculate the mean. Do not include “rough” in mean

Concentration - mole calculations

Concentration is the measure of how much acid (or alkali) is dissolved in the solution. Measured in mol/dm3

Calculation for concentration

Concentration= number of moles x1000/volume

Calculation for no. Moles

Mass/relative formula mass

Titration calculation

1. Calculate the number of moles using n= cv/1000

2. Using the balanced symbol equation and mole ratio deduce the number of moles of the second solution

3. Calculae the concentration using c=nx1000/v

Acid strength

This is related to how much of the dissolved acid changes into H+ ions

Strong acids

Acid fully splits up into H+ ions

Weak acid

Acid only partially splits up into H+ ions

Hydrochloric and ethanoic acid reactions

Hyrochloric= strong acid, ethanoic = weak acid

• Both react with metals,bases and carbonates in the same way. Eg. Fizz but because etah

How are Insoluble salts formed - precipitation

Some salts are insoluble in water. They can be made of mixing together solutions of solube slats. Eg lead iodide is insoluble in water, if you mix together lead nitrate and potassium iodide, both soluble, you will see a precipitation of insoluble lead iodide form

Ionic equation for precipitations

• Use the ions table to find the ions that make the precipitate and put these on the left of the equation.

• Work out the formula of the insoluble slatand put this on the right of the equation

• Include state symbols

• Balance