SSC
The law stating that the total pressure of a mixture of non-reacting gases equals the sum of their partial pressures was given by:
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Answer: Option D — John Dalton
Detailed Solution
Dalton's law of partial pressures was formulated by the English chemist John Dalton in 1801. It states that the total pressure exerted by a mixture of non-reacting gases is equal to the sum of the partial pressures of the individual gases, at constant temperature and volume.
Mathematically: P(total) = P1 + P2 + P3 + ...
Here, P1, P2, P3 and so on are the partial pressures of the individual gases. The partial pressure of a gas is the pressure it would exert if it alone occupied the whole volume of the container at the same temperature.
The partial pressure of each gas is also equal to its mole fraction multiplied by the total pressure. For example, air at sea level has a total pressure of about 1 atmosphere (101.3 kPa). Since oxygen makes up about 21% of air, the partial pressure of oxygen is about 0.21 atmosphere.
Applications of Dalton's law:
Gas collected over water: when a gas such as hydrogen or oxygen is collected over water in a laboratory, it is mixed with water vapour. The pressure of the dry gas is found by subtracting the vapour pressure of water (called aqueous tension) from the total pressure.
Breathing and diving: at high altitudes, the total air pressure is lower, so the partial pressure of oxygen is lower, which can cause altitude sickness. Deep-sea divers breathe gases at high pressure; at great depths, the high partial pressure of nitrogen can cause nitrogen narcosis, so divers often use special mixtures such as heliox (helium and oxygen).
Gas exchange in the lungs: oxygen moves from the alveoli to the blood, and carbon dioxide moves the other way, because of differences in their partial pressures.
John Dalton is best known for his atomic theory (1803-1808), which stated that all matter is made of tiny indivisible particles called atoms. He also studied colour blindness, which he himself had; the condition is sometimes called "Daltonism".
Why not the other options?
- ✗Robert Boyle gave the pressure-volume law (1662).
- ✗Jacques Charles gave the volume-temperature law (1787).
- ✗Thomas Graham gave the law of diffusion of gases (1848).
Quick tip
Remember: Dalton's law (1801) = P(total) = P1 + P2 + P3 ...; used for gas collected over water (aqueous tension) and diving; Dalton also gave the atomic theory and studied colour blindness.
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Matter & Its States — Preparation
This question tests your understanding of Matter & Its States, a key topic in the General Knowledge section. The detailed solution above uses a step-by-step approach to show the reasoning, and where available, a shortcut that helps you solve similar questions in under 90 seconds during the actual exam.
This topic covers matter and its classification: the states of matter, changes of state (melting, evaporation, sublimation and condensation), elements, compounds and mixtures, solutions, colloids and suspensions, and methods of separating mixtures. Exam questions often ask about examples of sublimation (camphor, naphthalene and dry ice), which substances are colloids (milk, fog and blood), and which method separates which mixture, such as chromatography for the colours in ink and fractional distillation for crude oil. Know the difference between a physical change and a chemical change. Practise the matter and its states questions below, written in the style of the general awareness sections of exams such as SSC, banking, railways, CUET GAT, MAH CET and CLAT. Each question comes with a detailed explanation that adds related facts, so every question helps you revise more than one point.