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To determine the purity of a substance, test its melting point or boiling point.
If it melts or boils at a fixed temperature, it is a pure substance.
Another method is to carry out a chromatography of the substance.
If it separates out into only one spot on the chromatogram, it is a pure substance.
A small amount of concentrated sample is placed on the starting line of a chromatography paper. The chromatography paper is placed inside a beaker containing a solvent. The solvent level should be below the starting line.
As the solvent moves up the paper, it separates the sample into its respective components.
The chromatography paper is removed before the solvent reaches the edge of the other end of the paper.
Rf = Distance travelled by sample / Distance travelled by solvent
| Mass | Weight |
|---|---|
| A measurement of the amount of substance in a body. | A measurement of the amount of gravitational force acting on a body |
| SI Unit: kilogram (kg) | SI Unit: newton (N) |
| Constant regardless of the gravitational field strength | Varies according to the gravitational field strength |
| Measured by a beam balance or electronic balance | Measured by a spring balance |
| Scalar quantity | Vector quantity |
It is a physical quantity with only numerical magnitude.
Examples: mass, energy, time, volume, density, power, temperature, speed.
It is a physical quantity with both numerical magnitude and direction.
Examples: force, velocity, acceleration, weight, displacement.
A physical quantity is a quantity that can be measured.
It consists of a numerical magnitude and a measurement unit.
Eg, length, area, volume, velocity, acceleration
Downward delivery: chlorine gas, carbon dioxide gas, sulfur dioxide gas
Upward delivery: hydrogen gas, ammonia gas
Displacement of water: hydrogen gas, carbon dioxide gas