MYP Chemistry Topic Formation of Salts Revision Notes

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MYP Chemistry Topic Formation of Salts Revision Notes | RevisionDojo

What is a Salt?

In chemistry, a salt is an ionic compound made of:

Positive ions (cations) – often from a metal or the ammonium ion (NH₄⁺)
Negative ions (anions) – usually from an acid

These ions are held together by electrostatic attraction (ionic bonding) in a regular giant lattice.

Hint

Key idea: A salt is formed when the H⁺ ions of an acid are replaced by metal ions or ammonium ions.

Example

Sodium chloride, NaCl – table salt (from HCl and NaOH or Na metal).
Potassium nitrate, KNO₃ – fertiliser (from HNO₃ and KOH).
Calcium sulfate, CaSO₄ – plaster, gypsum (from H₂SO₄ and CaCO₃ or CaO).
Ammonium chloride, NH₄Cl – in some fertilisers and dry cells (from NH₃ and HCl).

Salts in Solution – Neutral, Acidic or Basic?

When a salt dissolves in water, its ions interact with water.
Depending on the strength of the acid and base it came from, the solution can be:
1. Neutral – salt of strong acid + strong base (e.g. NaCl, KNO₃).
2. Basic – salt of weak acid + strong base (e.g. Na₂CO₃, CH₃COONa).
3. Acidic – salt of strong acid + weak base (e.g. NH₄Cl).
For MYP level, remember:
1. Salts from strong acid + strong base → usually neutral solutions.
2. Salts from weak acid + strong base → basic solutions.
3. Salts from strong acid + weak base → acidic solutions.

How are Salts Formed?

Acid-Base Neutralization

A neutralization reaction between an acid and a soluble base (alkali) produces salt and water.
General word equation: $$\text{Acid} + \text{Base} \to \text{Salt} + \text{Water}$$

Example

Note

Sodium sulfate from sulfuric acid and sodium hydroxide:

$$\mathrm{H}_2 \mathrm{SO}_4(\mathrm{aq})+2 \mathrm{NaOH}(\mathrm{aq}) \rightarrow \mathrm{Na}_2 \mathrm{SO}_4(\mathrm{aq})+2 \mathrm{H}_2 \mathrm{O}(\mathrm{l})$$

Note

Tip

This method is used especially when both reactants and the salt are soluble.
To get the solid salt, you evaporate water and allow crystals to form (crystallisation).

Metal and Acid Reaction

Acids can react with reactive metals to form salt and hydrogen gas.
General word equation: $$\text{Metal} + \text{Acid} \rightarrow \text{Salt} + \text{Hydrogen gas}$$

Example

Magnesium and hydrochloric acid:

$$\text{Mg}(s) + 2\text{HCl}(aq) \rightarrow \text{MgCl}_2(aq) + \text{H}_2(g)$$

Tip

This method is suitable for:

Metals above hydrogen in the reactivity series (e.g. Mg, Zn, Fe).
Not suitable for very reactive metals (too dangerous) or unreactive metals (no reaction).

To prepare a salt:

Use excess metal to ensure all acid is used up.
Filter off unreacted metal.
Evaporate the solution to obtain salt crystals.

Acid + Insoluble Base (Metal Oxide or Metal Carbonate)

Some bases are insoluble in water (e.g. CuO, CaCO₃), but they still neutralize acids.

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MYP Chemistry Formation of Salts Notes

What is a Salt?

Salts in Solution – Neutral, Acidic or Basic?

How are Salts Formed?

Acid-Base Neutralization

Metal and Acid Reaction

Acid + Insoluble Base (Metal Oxide or Metal Carbonate)

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Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

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What is a Salt?

Salts in Solution – Neutral, Acidic or Basic?

How are Salts Formed?

Acid-Base Neutralization

Metal and Acid Reaction

Acid + Insoluble Base (Metal Oxide or Metal Carbonate)

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Duis aute irure dolor in reprehenderit

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Periodic table5 subtopics

Matter5 subtopics

Types of chemical reaction18 subtopics

International Union of Pure and Applied Chemistry (IUPAC)4 subtopics

Pure and impure substances2 subtopics

The atmosphere2 subtopics

Bonding4 subtopics

MYP Chemistry Formation of Salts Notes

Periodic table5 subtopics

Matter5 subtopics

Types of chemical reaction18 subtopics

International Union of Pure and Applied Chemistry (IUPAC)4 subtopics

Pure and impure substances2 subtopics

The atmosphere2 subtopics

Bonding4 subtopics

What is a Salt?

Salts in Solution – Neutral, Acidic or Basic?

How are Salts Formed?

Acid-Base Neutralization

Metal and Acid Reaction

Acid + Insoluble Base (Metal Oxide or Metal Carbonate)

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

Unlock the rest of this chapter with a free account

What is a Salt?

Salts in Solution – Neutral, Acidic or Basic?

How are Salts Formed?

Acid-Base Neutralization

Metal and Acid Reaction

Acid + Insoluble Base (Metal Oxide or Metal Carbonate)

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

Unlock the rest of this chapter with a free account