Terms and Definitions
Accuracy – The extent to which an experimental result agrees with a known or correct value
Precision – the extent to which an experiment is reproducible
Scientific Notation – a system of representing large numbers, following the model a x 10b where a and b is number of places the decimal place had to move in order to express a in manageable terms. E.g. 1,123,000,000 is represented as 1.123 x 10^9
Significant figures – digits in a recorded value that are reliable and believable
Units – a uniform standard of measurement
When trying to describe the quantity or quality of something, whether a chemical substance or physical phenomenon, it is helpful to have some standard measure to refer to. A unit is nothing more than a standard by which a measured value can be described.
System of Units
There are 2 different sets; British engineering units and the metric system (also called the standard international (SI) system)
Intensity of light
Amount of a substance
To make things simpler when expressing very large or small values, scientists express values in terms of "a x 10b", where a is the value and b is number of places the decimal place had to move in order to express a in manageable terms. This type of expression is called scientific notation. Some easy examples of scientific notation are provided below.
1 = 1x100
10 = 1x101
100 = 1x102
1000 = 1x103
and so forth.
The value in the exponent place describes how many zeroes there are in the number being represented. The number 100 has 2 zeroes; it's scientific notation is 1X102.
In the case of numbers smaller than one, the exponent becomes negative, and that negative value represents how many zeroes there are between the number and the decimal place:
0.1 = 1x10-10.01 = 1x10-20.001 = 1x10-3
As one can imagine, when expressing extremely large numbers, this method is most helpful. For instance, take the number 602,200,000,000,000,000,000,000. Using scientific notation, this number can be expressed as 6.022x1023, which is obviously much more convenient.
Many, many numbers in chemistry, physics, and other sciences will appear in the scientific notation form. It pays to understand it. As we shall see in the next section, scientific notation also is generally more compliant with the rules of significant figures.
Five rules govern significant figures:
1. Non-zero digits are always significant; 1.121 has four significant digits.
2. Any zeros between two significant digits are significant; 1.08701 has six significant digits.
3. Zeros before the decimal point are placeholders and not significant; in the number .00254, only the 2,5 and 4 are significant, meaning the number has 3 significant figures.
4. Zeros after the decimal point and after figures are significant; in the number 0.2540, the 2,...