Time, Temperature, Mass & Volume
Time
- Time can be measured using a stopwatch or stopclock which are usually accurate to one or two decimal places
- The units of time normally used are seconds or minutes although other units may be used for extremely slow reactions (e.g. rusting)
- 1 minute = 60 seconds
Temperature
- Temperature is measured with a thermometer which can normally give readings to the nearest degree Celsius
- Digital thermometers are available which are more precise than traditional thermometers
- Traditional thermometers rely upon the uniform expansion and contraction of a liquid substance with temperature; they tend to be more accurate than digital thermometers which often need to be re-calibrated
- The units of temperature are degrees Celsius (ºC)
Mass
- Mass is measured using a digital balance which normally give readings to two decimal places. These must be tared (set to zero) before use
- The standard unit of mass is kilograms (kg) but in chemistry grams (g) are most often used
- 1 kilogram = 1000 grams
Volume-liquids
- The volume of a liquid can be determined using several types of apparatus, depending on the level of accuracy needed
- For approximate volumes where accuracy isn´t an important factor, measuring cylinders are used. These are graduated (have a scale so can be used to measure) and are available in 25 cm3, 50 cm3, 100 cm3 and 250 cm3
- Pipettes are the most accurate way of measuring a fixed volume of liquid, usually 10 cm3 or 25 cm3
- Burettes are the most accurate way of measuring a variable volume of liquid between 0 cm3 and 50 cm3 (e.g. in a titration)
Diagram of a burette with conical flask and pipette with filler
Volume-gases
- The volume of a gas sometimes needs to be measured and is done by collecting it in a graduated measuring apparatus
- A gas syringe is usually the apparatus used
- A graduated cylinder inverted in water may also be used, provided the gas isn’t water-soluble
- If the gas happens to be heavier than air and is colored, the cylinder can be used upright
Diagram of the set-up for an experiment involving gas collection
