Importance of Scientific Measurements in Chemistry

An essential element of all sciences is obtaining proper measurements. The International System of Units, known as SI Units, was developed by scientists to
standardize measurements across all sciences. Even with a standardized system, though, there is plenty of uncertainty that can come into play. The uncertainty must be minimized to ensure proper understanding of a process or experiment.

SI Units

Scientific measurements quantify the magnitude of something, described with a unit. For example, length is quantified in meters. However, because there are many different units -- e.g., inches, feet, centimeters -- scientists developed SI units to avoid confusion. Using common units, scientists from different countries and cultures can easily interpret each others' results. SI units include 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 and candela (cd) for luminous intensity.

Accuracy and Precision

When taking scientific measurements, it is important to be both accurate and precise. Accuracy represents how close a measurement comes to a true value. This is important because bad equipment, bad data processing or human error can lead to inaccurate results, meaning they are not very close to the truth. Precision is how close a series of measurements of the same thing are to each other. Measurements that are not precise do not properly identify random errors and can yield a widespread result that is not helpful.

Significant Figures
Measurements can be only as accurate as the limitations of the measuring instrument allow. For example, a ruler marked in millimeters can be accurate only up to the millimeter, because that is the smallest unit available. When a measurement is made, its accuracy must be preserved. This is achieved through "significant figures." The significant figures in a measurement are all the digits that are known for certain, plus the first one that is uncertain. For example, a meter stick delineated in millimeters can measure something to be accurate to the fourth decimal place. If the measurement were 0.4325 meters, there would be four significant figures.

Significant Figures Limits
Any non-zero digit in a measurement is a significant figure. Zeroes that occur before a decimal point are also significant. Also, zeroes that appear after a non-zero digit in a decimal value are considered significant. Whole number values, such as a full known quantity like five apples, is considered to have no impact on the significant digits of a calculation.

Multiplying and Dividing Significant Figures
When multiplying or dividing measurements, count the significant figures in the numbers. Your answer should have the same number of significant figures as the original number with the lowest number of significant digits. For example, the answer to the problem 2.43 x 9.4 = 22.842 should be converted to 23, rounding up from the partial number.

Adding and Subtracting Significant Figures
When adding or subtracting measurements, the number of significant figures is determined by the placement of the largest uncertain digit. For example, the answer to the problem 212.7 + 23.84565 + 1.08 = 237.62565 should be converted to 237.6, because the largest uncertain digit is the .7 in the tenths place in 212.7. No rounding should take place because the 2 that follows the .6 is smaller than 5.

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