![]() ![]() Averaging: We have special rules for averaging multiple measurements.The volume had 5 significant digits, but the number of moles only had 4 significant digits, so you are left with just 4 significant digits in your answer. For example, if you dissolve 0.3829 moles of a substance in 1.0000 L of water, then the concentration is 0.3829 moles per liter. Multiplying/dividing: Use the least number of significant digits involved in the calculation.See how fast you can lose significant digits in the lab? For example, if you measure a temperature change from 25.0 ☌ to 28.1 ☌, 28.1 – 25.0 = 3.1 ☌. Adding/subtracting: Use the least number of decimal places involved in the calculation.Significant digits from common calculations You always estimate one more digit than you can read from the lines. Mercury thermometers give more significant digits, but they have fallen out of favor due to safety concerns when they (inevitably) break. This means that we can only read 3 significant digits for temperatures between 10 and 99.9 ☌, and we only get 2 significant digits for temperatures between 0 and 9.9 ☌. Temperature – our red and blue alcohol thermometers are read to the nearest 0.1 ☌.For example, if you are making a hot water bath with approximately 400 mL of water (1 significant digit), then it is appropriate to use a beaker measure that volume. Repeat after me: “Erlenmeyer flasks and beakers are not designed to measure volumes,” although they can be used to get a rough estimate if the volume is not critical.You will normally estimate to the nearest 1/5th between lines. You always estimate one more digit than you can read from the lines. Typically you will get 3 significant digits from a graduated cylinder. The number of decimal places you can read is printed on the glass for your reference. Our lab is equipped with many different graduated cylinders, and the number of significant digits they give you depends on the exact graduated cylinder you are using and the volume you are measuring. Graduated cylinders are the most flexible tool for measuring volume.Our lab is equipped with burets that measure to the nearest 0.01 mL, so a volume greater than 1 mL will have 3 significant digits, and a volume greater than 10 mL will have 4 significant digits. You always estimate one more digit than you can read from the lines and estimate to 1/5th between lines. Burets are very precise tools for measuring volume.The number of significant digits you get from a micropipette is printed on the pipette for your reference, but it is usually about 4 significant digits. Micropipettes are very precise tools for measuring extremely small volumes (less than one milliliter).The precision is usually printed on the flask for reference. For example, a precision 1 liter volumetric flask filled exactly to the line etched on the neck contains 1.0000 L, which is 5 significant digits. ![]() ![]() Volumetric flasks are extremely precise tools for measuring volume and often give you 4 or more significant digits, depending on the size of the volumetric flask.That is the maximum mass for one of our balances. Higher masses give you more significant digits until you reach the capacity of the balance. For example, 0.5012 g of a substance has 4 significant digits. Mass – analytical balances generally give many significant digits, particularly when weighing 0.1 g or more, you get 4, 5, 6, or 7 significant digits.Background Significant digits from common measurements Although your results should be similar every time, the number of significant digits you get will vary depending on the uncertainty associated with the measurement techniques. In this lab, you will be measuring the density of water using a variety of tools. When your measurement has a limited number of digits, your subsequent calculations will also have a limited number of digits. Rules about significant figures may seem arbitrary from a theoretical standpoint, but in the laboratory you will see that they allow you to determine the precision of your measurements and calculations. Learning goals: follow instructions to complete a chemistry experiment, collect and analyze experimental data, explain likely sources of experimental error, w ork collaboratively with a lab partner. ![]()
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