By Kevin Carr, Updated Aug 30, 2022
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In chemistry, precise measurement is not a luxury—it is a necessity. A single misstep in quantification can cascade into flawed conclusions. To mitigate this risk, scientists rely on the International System of Units (SI) as a universal standard, coupled with rigorous practices that ensure both accuracy and precision.
Use SI units, uphold accuracy and precision, and respect significant figures to guarantee reliable results in the lab.
The SI system—established by the General Conference on Weights and Measures—provides a coherent set of base units: meters (m) for length, liters (L) for volume, kilograms (kg) for mass, seconds (s) for time, Kelvin (K) for temperature, ampere (A) for electrical current, mole (mol) for amount of substance, and candela (cd) for luminous intensity. By expressing every measurement in these units, researchers worldwide can interpret data without ambiguity.
Accuracy refers to how close a measurement is to the true value, while precision denotes the reproducibility of repeated measurements. A highly accurate instrument may still produce imprecise readings if it fluctuates between trials. Conversely, an instrument that delivers tightly clustered results may be systematically offset from the true value. Both attributes are essential for credible data.
Instrument resolution dictates the limit of precision. For instance, a millimeter‑graduated ruler can resolve up to ±0.001 m. When reporting a measurement, the number of significant figures must reflect this limitation. A value of 0.4325 m carries four significant figures, indicating confidence to the fourth decimal place.
• Every non‑zero digit is significant.
• Leading zeros are placeholders and not significant.
• Trailing zeros in a decimal number are significant.
• Whole numbers without a decimal point are ambiguous; use a decimal to indicate significance.
When multiplying or dividing, the result should be rounded to the least number of significant figures among the operands. Example: 2.43 × 9.4 = 22.842 → 23 (two significant figures).
For sums and differences, the result must be rounded to the least precise decimal place. Example: 212.7 + 23.84565 + 1.08 = 237.62565 → 237.6 (tenths place).
