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Volume Measurements
Liquids in Graduated Cylinders
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You should be able to measure the volume of liquids in a graduated
cylinder. How precisely you can measure volume depends on the size and type of graduated
cylinder you use. Generally, you should be able to estimate between the etched or printed
lines. |
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It is important to notice what each line or interval on the graduated
cylinder represents. Different kinds of graduated cylinders are set up differently. A 10
milliliter cylinder, for example, usually has one tenth of a milliliter for each
graduation, but some have two-tenths milliliter for each graduation. The way to check this
is to count the divisions between consecutive numbers. Here we have the usual 10 divisions
from one number to the next; therefore, the volume increment for each of those lines is a
tenth of a milliliter. Estimating your measurements by reading between the lines, you
should be able to measure to a hundredth of a milliliter. |
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On this 100 milliliter cylinder, the numbers are 10, 20, 30, etc., so
there is a 10 milliliter increment between them. Since there are 10 divisions between
consecutive numbers, each division represents one milliliter. Therefore, you should be
able to estimate to tenths of a milliliter by reading between the lines. |
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On some cylinders, there may only be five divisions between numbers. Or
there may be ten divisions for a 2 milliliter increment. In these cases, each of the
divisions represents 0.2 milliliters, rather than 0.1. You need to be aware of that when
you're using the cylinders like these, and adjust your between-line-estimates accordingly.
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The Meniscus
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A characteristic of liquids in glass containers is that they curve at the
edges. This curvature is called the meniscus. You measure the level at the horizontal
center or inside part of the meniscus. With water in glass, the meniscus will curve up at
the edges and down in the center so we say you read the bottom of the meniscus. |
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There are some materials where the curve goes the other way. Still, you
read the horizontal center of the meniscus. In this case it would be the top of the
meniscus. |
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In some plastic cylinders water has a flat surface. In that case top or
bottom doesn't matter, but we can still say use the center rather than the edges. |
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The visibility of the meniscus can be enhanced by using a card with a dark
stripe on it, placed behind the cylinder. Adjusting the placement of the card
can give you either a white meniscus against a black background or a black meniscus
against a white background. |
Now, or when you are in the lab, read through the instructions and complete Exercise 10
in your workbook, and have an instructor check the volume measurements that you make.
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