Revision: Practical Work Chemistry (English Medium) ICSE Class 9 CISCE

Oil spills are the accidental discharges of petroleum into oceans or estuaries. The sources of spills are overturned oil tankers, offshore oil mining, and oil refineries.

Water pollution means any change in the water quality which makes it unsuitable for use by humans and by other living organisms.

The pOH of a solution can be defined as the negative logarithm to the base 10, of the molar concentration of OH⁻ ions in solution.

pOH = -log₁₀[OH^-]

The pH of a solution is defined as the negative logarithm to the base 10, of the concentration of H⁺ ions in solution in mol dm^–3.

pH is expressed mathematically as

pH = -log₁₀ [H⁺] or pH = -log₁₀ [H₃O⁺]

pH scale is a scale for measuring the hydrogen ion concentration in a solution.

The amount of heat that is needed to raise the temperature of a unit mass of a substance by 1°C is called specific heat capacity.

• Blue/green salts may indicate Cu²⁺, Fe²⁺, or Fe³⁺ ions.
• White salts can suggest Pb²⁺, Zn²⁺, Ca²⁺, Na⁺, K⁺, or NH₄⁺ ions.
• Ammonia smell suggests NH₄⁺, H₂S smell indicates sulphides, and SO₂ smell indicates sulphites.
• Amorphous salts may indicate carbonates (CO₃²⁻).
• Hygroscopic/deliquescent salts point to Cl⁻ or NO₃⁻ ions.

1. The pH scale (0–14) measures the concentration of H⁺ ions in a solution; values < 7 indicate acids, > 7 indicate bases, and 7 is neutral.
2. A universal indicator shows different colours at different pH levels, helping to determine the strength of an acid or base.
3. Strong acids/bases produce more H⁺ or OH⁻ ions in solution, while weak acids/bases produce fewer ions at the same concentration.