All scientists measure time, temperature, mass, and volume differently. However, in order to standardize and improve communication, the Standard International Unit (S.I. unit) is used.
Measurement of Time
- The S.I. unit for time is second (s)
- Other units for measuring time include: minute (min) and hour (h)
- Some of the instruments used to measure time (especially in the laboratories) are: stopwatches, ticker tape timer
- Stopwatches are the most commonly used instruments as they are quite accurate (to about 0.01 s), is cheap, easy, and convenient to use
- A ticker tape timer is more commonly used in physics experiments to analyze the motion of an object
Measurement of Temperature
- The S.I. unit for temperature is Kelvin (K)
- Other units for measuring temperature include: Celsius (∘C)(∘C) and Fahrenheit (∘F)(∘F)
- The Kelvin scale is related to the Celsius scale by the equation: Temperature in K = Temperature in ∘C∘C + 273
- Some of the instruments used to measure temperature are: mercury thermometers, clinical thermometers, and data loggers with temperature sensors attached to it
- A mercury thermometer can measure temperatures ranging from −10∘C−10∘C to 110∘C110∘C, with each division measuring 1∘C1∘C change in temperature. It has an accuracy of ±0.5∘C±0.5∘C, is cheap and easy to use
- A data logger is more commonly used in field experiments where the data is collected over long periods. The temperature measured is more sensitive and accurate than that from a mercury thermometer. (A data logger can also measure the humidity of an environment, pH of fluids, etc)
Measurement of Mass
- The S.I. unit of mass is the kilogram (kg)
- Other units include: gram (g), tonne
- Some of the instruments used to measure mass: are beam balance, electronic balance
- A beam balance is seldom seen in chemistry labs nowadays as compared to an electronic balance. The latter is precise (has an accuracy of up to 0.01 g) and fast in obtaining the mass
Measurement of Volume
- The S.I. unit of volume is cubic meter (m3m3)
- Other units include: cubic centimeters (cm3cm3), liter (l), milliliter (ml)
- 1 litre (l) = 1 cubic decimetre (dm3dm3) = 1000 cubic centimetres (cm3cm3)
- 1000 litre (l) = 1 cubic metre (m3m3)
- The following table shows some of the common apparatus used to measure volume:
|Beaker||Used when precision is not needed. Can measure up to 50 cm350 cm3 of liquid.|
|Measuring cylinder||More accurate than a beaker. Can measure up to the nearest cm3cm3.|
|Burette||Can precisely measure the volume of a liquid to the nearest ±0.1 cm3±0.1 cm3. It has a graduated scale in divisions of 0.1 cm30.1 cm3.|
|Pipette||Can precisely measure fixed volumes of liquid like 25 cm325 cm3 or 50 cm350 cm3.|
When a liquid is poured into a glass container, there would be a curved surface at its top. This curved surface is called a meniscus. To accurately determine the volume of the liquid, read at the level of the liquid to prevent parallax error. If the meniscus is concave, read the scale at the bottom of the meniscus. If the meniscus is convex, read the top of the scale where the meniscus is.
The metric system, or international system (SI), is used to describe measurements of many quantities, such as length, mass, volume, and temperature.
In the laboratory, mass is measured with a balance (figure below), which must be calibrated with a standard mass so that its measurements are accurate. Other common units of mass are the gram and the milligram. A gram is 1/1000th of a kilogram, meaning that there are 1000g in 1kg.
Measurement of Time
The S.I. unit for time is second (s)
Other units for measuring time include: minute (min) and hour (h)
Some of the instruments used to measure time (especially in the laboratories) are: stopwatches, ticker tape timer.
Volume is the amount of space occupied by a sample of matter. The volume of a regular object can be calculated by multiplying its length by its width and its height. Since each of those is a linear measurement, we say that units of volume are derived from units of length.