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Chemistry · Grades 10–12

Calibration, blanks and uncertainty

Use the supplied relationship within its validated range.

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Calibration

Known reference values relate measured signal to concentration or another quantity.

Blank

A blank helps estimate background from the solvent, reagents or instrument.

Linear model

For a supplied S = mc + b, solve c = (S − b)/m; do not assume b = 0.

Range

Extrapolation outside the measured range can be unreliable.

Worked examples

For a stated calibration S = 2c + 0.1, a signal is 0.9. Find c in the calibration's concentration units.

c = (0.9 − 0.1)/2 = 0.4.

0.4

What is the main purpose of a blank measurement?

A blank helps identify non-analyte signal.

Estimate a background contribution.

Check your understanding

  1. Three readings are 4.0, 4.2 and 4.1. Find their arithmetic mean.

  2. A calibration covers 0 to 10 units. Predicting a value at 50 units is what?

    1. A direct measurement of a standard.
    2. Interpolation.
    3. Extrapolation.

  3. Why can repeated measurements be precise but inaccurate?

Answers and marking notes

Answers and marking notes
  1. 4.1

    The sum is 12.3, divided by three.

  2. Extrapolation.

    The prediction lies outside the tested range.

  3. They can cluster while sharing a systematic bias.

    Calibration errors can shift all readings similarly.

Further reading and review references

These are reference links, not copied exercises, institutional endorsement or proof of independent review.

Independent educational review required. Grade bands are approximate; these are not officially aligned curricula.