CC8 - Acids and Alkalis

Main hazard symbols

Corrosive, harmful to the environment and flammable.

Safety precautions when handling acids

Wear gloves, avoid contamination of local water, wear goggles.

Ion present in all acidic solutions

Hydrogen ions [H+]

Ion present in all alkali solutions

Hydroxide ions [OH-]

pH range of acids and alkalis

Acid = 0-<7

Alkali = >7-14

Symbol equations for Hydrochloric acid, sulphuric acid and nitric acid.

HCl, H2SO4, HNO3

Colours of indicators in acids and alkalis.

Litmus: Acid = red, Alkali = blue

Phenolphthalein: Acid = colourless, Alkali = pink

Methyl Orange: Acid = red, Alkali = turns yellow

Ionic symbols for hydroxide, nitrate, carbonate and sulfate.

OH -, NO 3-, SO4 2-, CO2 3-

How to calculate concentration of a solution?

Concentration (g/dm3) = amount of dissolved solute (g) / volume of solution (dm3)

How to convert between cm3 and dm3?

Divide cm3 by 1000 to convert to dm3.

Link between pH and Hydrograph ion concentration

As the pH decreases by 1, the hydrogen ion concentration increases by a factor of 10.

Strong Acid

Molecules in the acid completely dissociate into hydrogen ions.

Weak Acid

The molecules in the acid do not completely dissociate into hydrogen ions.

Base

Any substance which reacts with an acid to produce a metal salt and water only.

What happens when a metal oxide reacts with an acid?

Acid + metal oxide → metal salt + water

How does reactivity of an acid depend on strength of an concentration?

As strength increases, so does reactivity.

As concentration increases, so does reactivity.

A concentrated weak acid can have the same reactivity as a dilute strong acid.

Link between pH and concentration of ions in acids and alkalis?

The higher the concentration of hydrogen ions in a solution, the lower the pH.

The higher the concentration of hydroxide ions in a solution, the higher pH.

Metal salt produced when reacting with hydrochloric, sulfuric and nitric acids.

Chloride salts, sulphate salts, nitrate salts.

State symbols for solid, liquid, gas and aqueous

(s), (l), (g), (aq)

What happens in a neutralisation reaction?

A metal salt and water is produced, solution is neutralised, temperature of solution increases.

Formula of the group 1 hydroxides

LiOH, NaOH, KOH

Formula of the group 2 hydroxides

Be(OH)2, Mg(OH)2, Ca(OH)2

Alkali

A soluble base

Word equation for a metal hydroxide reacting with an acid?

Acid + Metal Hydroxide → Metal Salt + Water

How would HCl and NaOH dissociate into hydrogen/hydroxide ions?

HCl (aq) → H+ (aq) + Cl- (aq)

NaOH (aq) → Na+ (aq) + OH- (aq)

Why is titration used used to prepare soluble salts?

A titration reacts the exact amount of acids and alkali to produce a solution of only salt and water.

4 steps to carry out an acid-alkali titration

1. Add acid to a burette and alkali to a conical flask

2. Add a few drops of indicator to the alkali

3. Slowly add the acid to the alkali by controlling the flow using the burette

4. When the indicator changes colour the solution is neutral and at an endpoint

Equation for a metal reactions with an acid

Metal + Acid → Metal salt + hydrogen

Equation for a metal carbonate reacting with an acid

Metal Carbonate + Acid → Metal Salt + Carbon dioxide + water

Tests for carbon dioxide and hydrogen

Carbon dioxide - bubble gas through limewater, if it turns cloudy carbon dioxide is present.

Hydrogen - squeaky pop test, can hear a squeaky pop noise if you light an air + hydrogen mix on fire.

Ionic equation

An equation that shows the ions involved in a chemical reaction.

Spectator ion

Ions which do not change into atoms/molecule during a reaction.

Half-equation

An equation that shows the gain or loss of electrons by ions to form atoms or molecules

Oxidation reaction

The loss of electrons

Reduction reaction

The gain of electrons

Precipitate

An Insoluble substance

What happens in a precipitation reaction?

The ions from the salts involved in the reaction swap.

4 Steps to produce a dry sample of an insoluble salt

1. Mix two solutions required to form the insoluble salt

2. Filter out the precipitate formed

3. Clean the precipitate using distilled water

4. Leave to dry

5 Steps to get a soluble salt from a metal oxide and an acid

1. Add excess metal oxide to an acid

2. Gently warm the mixture to speed up the reaction

3. Filter out the excess metal oxide from the solution

4. Evaporate most of the water out over a boiling water bath

5. Leave the remaining solution to evaporate slowly allowing for crystallisation to occur

Why is an excess of insoluble metal oxide used?

To make sure all acid is used up

Why is the excess metal oxide removed?

To make sure the final spat prepared is pure.