| Physical Quantity | SI Unit | Symbol |
| Length | metre | m |
| Mass | kilogram | kg |
| Temperature | Kelvin | K |
| Time | second | s |
| Current | ampere | A |
| Amount of substance | mole | mol |
| Luminous intensity | candela | cd |
Category: FAQs
Define Kinetic Particle Theory.
Kinetic Particle Theory states that all matter is made up of tiny, discrete particles that are in constant, random motion.
In paper chromatography, why must the start line be above the solvent level?
The start line above the solvent level allows the solvent to move past the start line, carrying the dissolved samples along with it.
With the start line below the solvent level, the samples on the start line will dissolve in the solvent right at the beginning, contaminating the whole solvent, causing the chromatogram to be inaccurate.
Explain the importance of the measurement of the purity of substances that we use in foodstuffs and drugs.
For substances used in preparing food and drugs, it is important to ensure that only permitted substances are being used.
If a substance is impure, and laced with some other substances, these unapproved impurities might not be safe for human consumption, and lead to undesirable effects on human health.
What are the 2 methods to determine the purity of a substance?
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.
Describe the process of paper chromatography.
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.
Write down the formula to find Rf value.
Rf = Distance travelled by sample / Distance travelled by solvent
Draw the set-up for obtaining pure water from salt water.
Describe the differences between mass and weight.
| 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 |
What is a scalar quantity? Give some examples.
It is a physical quantity with only numerical magnitude.
Examples: mass, energy, time, volume, density, power, temperature, speed.