One of the most important concepts that I had to learn when taking chemistry, in order to succeed in the quantitative aspect of the subject, was the meaning of significant figures and how they are used in chemistry.
When doing any calculation in chemistry, you will become familiar with the number of significant figures, or the the number of digits that are reported for the value of a quantity that has been either measured or calculated, which serves to indicate the precision of the value (Ebbing and Gammon 2009). When it comes to significant figures, there are a set of rules that are very important to follow, per Ebbing and Gammon:- Zeros at the beginning of a number are NOT significant digits. In some cases, zeros at the end of a number may also be insignificant. As an example, the values 0.32 cm, 3.4 cm, and 0.0000000033 cm all have 2 significant figures.
- Zeros at the end of a number that are preceded by a decimal point are significant figures. For instance, 3.30 cm, 3.00 cm, and 30.0 cm all have three significant figures.
- Zeros at the end of a number can be significant or insignificant. For instance, in the value 300 cm, there can be one, two, or three significant figures. If, however, the value was written as 300. cm, there three significant figures precisely. The decimal point at the end of the value makes the zeros significant in this case.
- And, as a note, to remove any uncertainty about the significance of zeros in a value, you can always write numbers using scientific notation.
Although you are sure to have studied scientific notation in elementary school, I’ll review this here because it will come in handy. When scientific notation is employed, a number is expressed as some number A multiplied by 10 to the power of n, where A is defined as a number with a single nonzero digit to the left of the decimal point, and n is an integer, or whole number. Let’s convert represent some numbers using the scientific notation. 300 cm would be represented as 3.0 x 10^2 cm if you were aiming for precision to two significant figures; 3.00 x 10^2 cm if you were aiming for precision to three significant figures, and so on… (Ebbing and Gammon 2009). Very small quantities can also be represented using scientific notation, such as 3.0 x 10^-4 cm, which is 0.00030 when written out fully, and there are two significant figures in this number, because according to rule one, zeros at the beginning of a number are not significant figures.In the next post, I will present some more rules on significant figures related to the calculations we will soon be doing in chemistry. These posts are truly the difference between earning an A and an F on an exam (if your professor is/was anything like mine was). Many professors, such as my professor, will stress this concept greatly and will continue to do so even as you are well into performing calculations in chemistry. Even if you do a very advanced calculation and get the correct answer, if you do not apply the rules of significant figures, you can lose lots of points, so always be careful and observant when submitting your final answers to questions.
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