Practical work - Facts
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Define hypothesis
A testable statement
Define independent variable
The variable that is changed
Define dependent variable
The variable that is measured
Define control variable
Variables that are kept constant to ensure valid results
Define repeatable
The same person can repeat it and get the same results.
Define reproducible
Different people can follow the method and get the same results.
State what makes something valid
Only the independent variable has been changed, the results are true
Explain why test tubes are not used to measure volume
No graduations
Explain when a water bath or heating plate is used instead of a Bunsen burner
if need to heat slowly or if the chemical is flammable
Give the apparatus used to transfer solids
Spatula.
Give the apparatus used to measure mass
Balance
Explain why a burette is more accurate than a measuring cylinder
Burettes can measure variable volumes and add volume one drop at a time
Give the apparatus used to transfer gas
Gas syringe / inverted measuring cylidner filled with water Filling with water can affect results if the gas is water soluble (systematic error)
Give the apparatus that measures temperature
Thermometer
Define resolution
The smallest change in a measured variable that an instrument can detect.
Define accuracy
The degree to which a measured value reflects the true value.
Define precision
The consistency of repeated measurements.
Define random error
Errors that occur due measuring above or below the true value Reduce by making repeat measuriments and ignoring anomalous reuslts to calculate mean
Define systematic error
Errors that occur consistently in the same direction, often due to faulty equipment.
Explain what causes a zero error
A zero error occurs when an instrument does not read zero because it has not been calibrated.
Explain what parallax error is
Parallax error occurs when measurements are read at an angle rather than directly in line with the scale.
Explain how to calculate uncertainty from a set of results
Calculate the range of the results and divide by two to find the uncertainty.
Explain how to calculate the uncertainty of a piece of apparatus
Determine the smallest division on the scale and divide by two.
Explain how to calculate the range
Subtract the smallest value from the largest value in a set of results.