What Is Solubility?

Solubility refers to the ability of a substance to dissolve in a solvent, usually water, to form a solution.

In chemistry, many salts dissolve in water, while others do not.

Understanding solubility rules helps chemists predict whether a salt will dissolve in water or form a precipitate.

These rules are especially important in chemical reactions and laboratory experiments.

What Are Solubility Rules?

Solubility rules are general guidelines used to determine whether a salt is soluble or insoluble in water.

These rules help chemists quickly predict the outcome of chemical reactions involving salts.

Salts That Are Always Soluble

Some salts dissolve easily in water.

The following salts are always soluble:

• All sodium salts
• All potassium salts
• All ammonium salts
• All nitrate salts

Examples include:

• Sodium chloride (NaCl)
• Potassium nitrate (KNO₃)
• Ammonium sulfate ((NH₄)₂SO₄)

These salts dissolve readily in water to form solutions.

Common Soluble Salts

Some salts are generally soluble with a few exceptions.

Chlorides

Most chlorides are soluble except:

• Silver chloride (AgCl)
• Lead(II) chloride (PbCl₂)

Sulfates

Most sulfates are soluble except:

• Barium sulfate (BaSO₄)
• Lead(II) sulfate (PbSO₄)
• Calcium sulfate (CaSO₄) (slightly soluble)

Common Insoluble Salts

Some salts are generally insoluble in water.

These include:

• Carbonates (except sodium, potassium and ammonium carbonates)
• Hydroxides (except sodium and potassium hydroxide)
• Silver salts such as AgCl

These salts often form precipitates when solutions are mixed.

What Is a Precipitate?

A precipitate is an insoluble solid that forms when two aqueous solutions react.

Precipitation reactions occur when ions combine to form a compound that does not dissolve in water.

Example:

AgNO₃ + NaCl → AgCl + NaNO₃

Silver chloride forms as a white precipitate.

Importance of Solubility Rules

Solubility rules are important because they help chemists:

• Predict precipitation reactions
• Identify unknown substances in experiments
• Understand water treatment and environmental chemistry
• Perform laboratory analysis

These rules are widely used in analytical chemistry.

Exam Tip (5070)

Students are often asked to:

• Identify whether a salt is soluble or insoluble
• Predict whether a precipitate will form
• Apply solubility rules in chemical reactions

Example exam question:

Will silver chloride dissolve in water?

Answer:

No, silver chloride is insoluble and forms a white precipitate.

Practice Question

Which of the following salts is always soluble in water?

A) Silver chloride
B) Sodium nitrate
C) Lead sulfate
D) Calcium carbonate

Answer

B) Sodium nitrate

All nitrate salts are soluble in water.

Study O Level Chemistry with IVY Online

Preparing for Cambridge O Level Chemistry (5070) becomes easier with clear explanations and exam-focused practice.

With the IVY Online App, students can access:

✔ Complete syllabus coverage
✔ Interactive concept explanations
✔ Topic-wise past paper questions
✔ Exam-focused revision

📱 Download the IVY Online App and start preparing smarter for Chemistry exams.