Proper measurement techniques ensure that you accurately measure the materials that you will use in your experiments. This is essential for reproducibility.
Liquid volumes should be measured with graduated or volumetric glassware, such as a volumetric flask, a graduated cylinder, or a volumetric pipette. Standard beakers and Erlenmeyer flasks should not be used for precise measurements.
Glassware marked ‘to contain’ will contain the specified volume of liquid when it is filled to the mark, but it may deliver slightly less than that volume. Glassware marked ‘to deliver’ will contain some extra liquid when it is filled to the mark, but it will deliver the precise volume specified.
Measurement error is the difference between the measured value and the true value. This is expressed as ‘uncertainty’, which describes the expected amount of variation between the measured and true values. Remember to write down the uncertainty of your instruments and glassware when you record your measurements.
Significant figures represent the precision of a value. All numbers other than leading or trailing zeroes are significant, including zeroes between non-zero digits. Trailing zeroes are significant only if they either follow a decimal point or are marked as significant using an overline, underline, or decimal point with no tenths place. Leading zeroes are never significant.
Source: Smaa Koraym at Johns Hopkins University, MD, USA
Here we show the laboratory preparation for 10 students working individually, with some excess. Please adjust quantities as needed.
| 1 Stirring rod |
| 1 20-mL volumetric flask |
| 1 10-mL volumetric pipette |
| 1 Pipetter |
| 1 600-mL beaker |
| 1 50-mL graduated cylinder |
| 1 12-in ruler |
| 1 Egg |
| 1 Eyedropper |
Source: Smaa Koraym at Johns Hopkins University, MD, USA
Here we show the laboratory preparation for 10 students working individually, with some excess. Please adjust quantities as needed.
| 1 Stirring rod |
| 1 20-mL volumetric flask |
| 1 10-mL volumetric pipette |
| 1 Pipetter |
| 1 600-mL beaker |
| 1 50-mL graduated cylinder |
| 1 12-in ruler |
| 1 Egg |
| 1 Eyedropper |
Ensure that you have acquired the necessary glassware and materials for the lab and set them out before the class begins. Each student will need 50 grams of sodium chloride. Obtain enough small plastic bottles with caps for the number of students and label them.
Using the top-loading balance, weigh 50 grams of sodium chloride directly into each bottle. Place the bottles of sodium chloride at the student workstations. Next, set out the necessary glassware at each station, including a stirring rod, a 20-milliliter volumetric flask, a 10-milliliter volumetric pipette and pipetter, a 50-milliliter beaker, a 600-milliliter beaker, and a 50-milliliter graduated cylinder.
Then, place one 12-inch ruler, one egg, and an eyedropper at each station. Finally, ensure that there is enough deionized water available in the lab. Fill enough 250-milliliter wash bottles with deionized water for each student to have one.
