BPGHS 2025 Sec 3 EOY Revision (3G)

2025 Sec 3 EOY Revision | Chemistry Revision notes for the upcoming Sec 3 EOY chemistry exam 🧪 1.1 | Measurements of Physical Quantities (Experimental Chem) Measurement of Time For measurement of time, a stopwatch is used. Common apparatus include digital stopwatch. Depending on the type of digital stopwatch, it can measure time up to 2 decimal places in seconds (e.g: 20.01 s). The SI unit for time is the second (s). Other units such as minute (min) and hour (h) could also be used. Table 1.1.1. The precisions and uncertainties of digital stopwatches Digital Stopwatch Precision/s Uncertainty of measurement/s D.P. Example timing/s 0.1 ±0.1 1 28.1 0.01 ±0.01 2 28.00 28.11 ⓘ Note Precision is determined by the smallest division on the instrument whereas uncertainty of measurement corresponds to the range where the actual value could fall into. For example, if a stopwatch has an uncertainty of ±0.01s, if its reading shows 28.00 s, it means the actual value could be anywhere in the range of 27.99 s to 28.01 s. Measuring of Temperature For measurement of temperature, a thermometer is used — alcohol thermometers and mercury thermometers . Temperature measured by a thermometer is recorded to the nearest 0.5 °C. The SI unit for temperature is the kelvin (K). Other units used include degree Celsius (°C). Temperature can also be recorded using a datalogger connected to a temperature sensor . The advantages of using a datalogger connected to a temperature sensor are: ● It is more accurate than the mercury or alcohol thermometer. ● It can record data continuously over a period of time. ● It saves data (in a computer) which can be used to produce graphs and charts Page 1 . Notes prepared by BPGHS 3G 2025 :)

Table 1.1.2. The precision and uncertainty of laboratory thermometers Thermometer Precision/ ℃ Uncertainty of measurement/ ℃ D.P. Example temperature/ ℃ 1 ±0.5 1 23.0 23.5 Measurement of Length For measurement of length in laboratory, metre rule and measuring tape are used. The SI unit for length is metre (m). Other units include mm, cm, dm. Table 1.1.3. The precision and uncertainty of a metre rule Metre rule Precision/mm Uncertainty of measurement/mm D.P. Example length/mm 1 ±0.5 1 20.5 Measurement of Mass For measurement of mass, an electronic balance is used. Mass measured by an electronic mass balance is recorded to the nearest 0.001 g, depending on the type of electronic mass balance used. The SI unit for mass i