Chemical measurements

• What is the purpose of the BBC Homepage?

  To provide access to news, sports, and educational resources
• What are the main sections listed on the BBC Homepage?

  News, Sport, Earth, Reel, Worklife, Travel, Culture, Future, Music, TV, Weather, Sounds
• What is the focus of the Bitesize section on the BBC website?

  To provide educational resources for various levels
• What does the term "relative formula mass" refer to in chemistry?

  It is the sum of the atomic masses of all atoms in a chemical formula
• What does the law of conservation of mass state?

  Mass is neither created nor destroyed in a chemical reaction
• What is meant by "chemical measurements"?

  It refers to the quantification of substances in chemical reactions
• What is the definition of uncertainty in chemical measurements?

  It is the interval within which the true value of a quantity can be expected to lie
• What are some causes of uncertainty in chemical measurements?

  Difficulty in judging measurements and instrument limitations
• How can uncertainty be estimated from measuring instruments?

  By considering the resolution and range of the instrument
• What is the resolution of a measuring instrument?

  It is the smallest change in a quantity that gives a change in the reading
• How is uncertainty estimated for a thermometer with a resolution of 1.0°C?

  The uncertainty is ± 0.5°C
• What is the uncertainty for a digital measuring instrument reading to 0.1 s?

  The uncertainty is ± 0.05 s
• How is uncertainty estimated from a set of repeat measurements?

  It is ± half the range of the measurements
• How do you calculate the mean volume from a set of measurements?

  By summing all measurements and dividing by the number of measurements
• Given the volumes 24.0, 24.5, 23.5, 25.0, and 23.0, what is the mean volume?

  The mean volume is $24.0 \text{ cm}^3$
• How do you calculate the range from a set of measurements?

  By subtracting the smallest value from the largest value
• What is the range of the volumes 24.0, 24.5, 23.5, 25.0, and 23.0?

  The range is $2.0 \text{ cm}^3$
• How do you estimate uncertainty from the range of measurements?

  By calculating ± half the range
• What is the uncertainty for the volumes 24.0, 24.5, 23.5, 25.0, and 23.0?

  The uncertainty is $± 1.0 \text{ cm}^3$
• How can uncertainty be represented on a graph?

  • Plot all repeat readings for each independent variable value
  • Use vertical lines to represent uncertainty
• What is the process for estimating uncertainty in measurements?

  1. Consider the resolution of measuring instruments
  2. Calculate the range from repeat measurements
  3. Estimate uncertainty as ± half the smallest scale division or half the range
• What are the steps to calculate mean volume and uncertainty from measurements?

  1. Sum all measurements
  2. Divide by the number of measurements for mean
  3. Calculate range (largest - smallest)
  4. Estimate uncertainty as ± half the range
• What is the significance of showing uncertainty on a graph?

  • It visually represents the reliability of measurements
  • It indicates the variability in data