INTRODUCTION TO MEASUREMENTS
Introduction: In the first three experiments you will learn how to use equipment that to measure length, mass, and volume. You will apply the rules about significant figures every time you make a measurement or a calculation involving measured quantities.
A measurement consists of a numerical value and a unit. Both have to be specified or the measurement is meaningless. For example if you say that you live 5.6 from campus, we don’t know if that means 5.6 miles, 5.6 blocks, 5.6 minutes by car etc
The concept of significant figures applies to measured quantities because of the uncertainty associated with every measuring device. It does not apply to exact numbers, such as counting numbers or numbers that are defined. The number of significant figures in a measurement is the number of figures that are known with confidence plus one figure that is approximate. The uncertain digit is the last of the number. One of the essential tasks you must do when you are asked to make a measurement is to investigate the measuring tool. How many digits can you read and in what decimal place is the doubtful digit, i.e. where is the uncertainty? Data is never rounded off.
Example: When weighing a sample of salt, of appx 3 grams, to the nearest 0.01g, the reading should be recorded to 2 decimal places – i.e. 3.01 g or 2.99 g or 3.00 g.
Any weighings made with an electronic balance should be recorded with all the digits shown on the screen. Because it is a delicate instrument that can be damaged easily, certain precautions should be taken.
1. Never place a chemical directly on the balance pan. Use a dry container
2. Never pour liquids into a container while it is on the balance!
3. All measurements need to be within the capacity of the balance.
4. Should a spill occur, clean it up immediately.
5. Never place any item that is hot onto the balance pan.
6. To weigh substances in...