Acids, Alkalis, Salts

What colour does litmus paper turn in acid?

Red

What colour does litmus paper turn in alkali?

Blue

What colour does phenolphthalein turn in acid?

Colourless

What colour does phenolphthalein turn in alkali?

Pink

What colour does methyl orange turn in acid?

Red

What colour does methyl orange turn in alkali?

Yellow

What is the pH scale?

How can you use universal indicator to find the pH of a solution?

1. Add a few drops of solution/dip indicator paper into aqueous solution

2. Observe + match final colour to pH scale

What are acids and what ions do they form?

• Acids are proton donors

• They dissolve in water to form positive hydrogen (H⁺) ions & aqueous solution

• Concentration of ions make the solution acidic

What is an example of an acid dissociating in water?

Acid: Hydrochloric acid

Word equation: HCL (aq) → H⁺ (aq) + Cl⁻ (aq)

What are alkalis and what ions do they form?

• Alkalis are proton receivers

• They dissolve in water to form negative hydroxide ions (OH⁻) & aqueous solution

• Concentration of ions make it alkali

What is an example of an alkali dissociating in water?

Alkali: Sodium hydroxide

Equation: NaOH (aq) → Na⁺ (aq) + OH⁻ (aq)

What is neutralisation?

Reaction which removes the acidity or alkalinity of a solution

What are the methods of neutralisation?

1. Alkali added to acid → increase pH level + form neutral solution

2. Acid added to alkali → decrease pH level + form neutral solution

What is the word equation of neutralisation?

Acid + Alkali → Salt + Water

What is the chemical equation of neutralisation?

H⁺ (aq) + OH⁻ → H₂O (l)

What are the general rules for solubility?

Soluble	Insoluble
All Sodium, Potassium, Ammonium	None
All nitrates	None
Common chlorides	Except Silver, Lead (II)
Common sulphates	Except, Barium, Calcium, Lead (II)
Except for Sodium, Potassium	Common carbonates
Except for Sodium, Potassium, Calcium (slightly)	Common hydroxides

What are the features of Acid + Metal reactions?

• Only metals above hydrogen in the reactivity series will react

• More reactive metal = more vigorous reaction

• Forms a salt + hydrogen gas

What is the word equation of Acid + Metal reactions?

Metal + Acid → Salt + Hydrogen

[A&M] What are the equations of Sulphuric Acid + Metal reactions?

[Metal] + H₂SO_{4 (aq)} → [Metal]SO_{4 (aq)} + H_{2 (g)}

_{Metal + Sulphuric Acid → Metal Sulphate + Hydrogen}

[A&M] What are the equations of Metal + Hydrochloric Acid reactions?

[Metal] + 2HCl _(aq) → [Metal]Cl_{2 (aq)} + H_{2 (g)}

_{Metal + Hydrochloric Acid → Metal Chloride + Hydrogen}

What are the features of Acid + Base reactions?

• Metal oxides + hydroxides are bases

• This is called a neutralisation reaction

• It forms a salt + water

What is the word equation of Acid + Base reactions?

Acid + Base → Salt + Water

[A&B] What are the equations of Metal Oxide + Sulphuric Acid reactions?

[Metal]O _(s) + H₂SO_{4 (aq)} → [Metal]SO_{4 (aq)} + H₂O_(l)

_{[Metal] Oxide + Sulphuric Acid → [Metal] Sulphate + Water}

[A&B] What are the equations of Metal Hydroxide + Hydrochloric Acid reactions?

[Metal]OH (s) + HCl (aq) → [Metal]Cl (aq) + H₂O (l)

_{[Metal] Hydroxide + Hydrochloric Acid → [Metal] Chlroide + Water}

[A&B] What are the equations of Metal Hydroxide + Nitric Acid reactions?

[Metal]OH_(s) + HNO_{3 (aq)} → [Metal] (NO₃)_(aq) + H₂O_(l)

_{[Metal] Oxide + Nitric Acid → [Metal] Nitrate + Water}

What is the method to obtain pure, dry crystals?

[1. Heat dilute acid with a bunsen burner

2. Add in base until in excess and stir with a glass rod]

3. Filter the mixture using funnel and filter paper to remove the excess base

4. Heat the filtered solution to evaporate some of the water

5. Leave the solution to cool and crystallise

6. Filter the solution, separating the liquid and obtaining crystals

7. Leave crystals to dry in a warm oven until mass doesn’t change

Why does a crystal experiment use excess base?

To neutralise the acid