Acids, Bases and Salts

Litmus in acid

Red

litmus in alkali

blue

Phenolphthalein in acid

Colourless

Phenolphthalein in alkali

Pink

Methyl Orange in acid

Red

Methyl Orange in alkali

Yellow

pH scale

0-14

pH scale Strongly acidic

0-4

pH scale Weakly acidic

4-6

pH scale neutral

7

pH scale weakly alkaline

8-10

pH scale strongly alkaline

10-14

What is universal indicator?

A mixture of different plant indicators which operate across a broad pH range and is useful for estimating the pH of an unknown solution

Describe the use of universal indicator to measure the approximate pH value of an aqueous solution

A few drops are added to the solution and the colour is matched with a colour chart which indicates the pH that matches with specific colours

When acids are added to water ...?

they form positively charged hydrogen ions (H+)

What makes a solution acidic?

the presence of H+ ions

When alkalis are added to water ...?

they form negative hydroxide ions (OH-)

What makes a solution alkali?

the presence of OH- ions

What is the pH scale?

a numerical scale which is used to show how acidic or alkaline a solution is. In other words, it is a measure of the amount of ions present in solution

When does a neutralisation reaction occur?

When an acid reacts with an alkali

What happens when an acid reacts in a neutralisation reaction with an alkali?

The H+ ions react with the OH- ions to produce water

Titrations

A method of analysing the concentration of solutions
Can be used to prepare salts

How to perform a titration

(See method in booklet 2.6)

Soluble ionic compounds

Compounds of sodium, potassium and ammonium
All nitrates
Nearly all chlorides
Nearly all sulphates
Sodium, Potassium, and Ammonium carbonates
Sodium Potassium, and calcium hydroxides

Insoluble Ionic compounds

Silver and lead (II) chlorides
Barium, calcium, and lead (II) sulphates
Nearly all carbonates
Nearly all hydroxides

Salt

A salt is a substance formed from an acid where the H+ ions in the acid are replaced by either metal ions or ammonium ions
Ionic compounds

Acids

Proton donors as they ionise in solution producing protons, H+ ions
These H+ ions make the aqueous solution acidic
Acids release H+ ions when dissolved in water

Alkalis are ________ bases

soluble

Bases (Alkalis)

Bases (alkalis) are proton acceptors as they ionise in solution producing OH- ions which can accept protons
These OH- ions make the aqueous solution alkaline
Alkalis dissolve in water to release OH- ions

A proton is the same as ...? And why?

a H+ ions because a hydrogen atoms only contains one proton and one electron. When a hydrogen ion is formed, the electron is lost and a proton is left behind

General equation for metals reacting with acid

metal + acid -> salt + hydrogen

Which metals will react with dilute acids?

only metals above hydrogen

Reaction of acids with bases makes ...?

Soluble salts

General equation in all acid-base neutralisation reactions

acid + base -> salt + water

Which substances act as bases?

Metal oxides, metal hydroxides and ammonium

Reactions of acids with metal carbonates make ...?

Soluble salts

General equation for the acids reacting with metal carbonates

metal carbonate + acid -> salt + carbon dioxide + water

Base

Substances which can neutralise an acid, forming a salt and water

Bases are usually ...?

Oxides, hydroxides or carbonates of metals

Describe an experiment to prepare a pure, dry sample of a soluble salt, starting from an insoluble reactant

(See method in booklet 2.7)

Solubility

The amount (mass) of solute needed for 100g of solvent to maintain a saturated solution at a certain temperature