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Getting started: working safely and accurately in the lab
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Chemistry papers ask about methods, hazards and measurements from the practicals. These skills begin with what you did in KS3 labs.
Hazards and safety
Flammable: catches fire easily (for example ethanol).
Corrosive: destroys living tissue such as skin and eyes (for example concentrated acids).
Toxic: can cause serious harm or death if swallowed, breathed in or absorbed through the skin.
Oxidising: helps other substances burn.
Harmful or irritant (exclamation mark): may cause irritation or less serious harm.
Wear eye protection, tie hair back and stand up when heating. Use the yellow safety flame on a Bunsen burner when it is not being used, and a blue flame (air hole open) for heating.
Corrosive: destroys living tissue such as skin and eyes (for example concentrated acids).
Toxic: can cause serious harm or death if swallowed, breathed in or absorbed through the skin.
Oxidising: helps other substances burn.
Harmful or irritant (exclamation mark): may cause irritation or less serious harm.
Wear eye protection, tie hair back and stand up when heating. Use the yellow safety flame on a Bunsen burner when it is not being used, and a blue flame (air hole open) for heating.
Measuring
Volume: a measuring cylinder (read the bottom of the meniscus at eye level), or a pipette or burette for more precise volumes.
Mass: a balance, in g. Temperature: a thermometer, in °C. Time: a stop clock, in s.
Choose equipment whose smallest division (resolution) suits the measurement.
Volume units: 1 cm3 = 1 ml, and 1 dm3 = 1000 cm3.
Mass: a balance, in g. Temperature: a thermometer, in °C. Time: a stop clock, in s.
Choose equipment whose smallest division (resolution) suits the measurement.
Volume units: 1 cm3 = 1 ml, and 1 dm3 = 1000 cm3.
Fair tests and means
Change one independent variable, measure the dependent variable and keep control variables the same.
Repeat readings, leave out anomalies, and calculate a mean.
Repeat readings, leave out anomalies, and calculate a mean.
A student measures a temperature rise three times: 21.0 °C, 22.0 °C and 21.5 °C. Find the mean.
- Total = 21.0 + 22.0 + 21.5 = 64.5
- Mean = 64.5 ÷ 3
Answer: 21.5 °C
Know the hazard words and safe practice. Read a meniscus at eye level from the bottom. 1 dm3 = 1000 cm3. Repeat, remove anomalies, calculate a mean.
Check you have got it
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