The mL graduations in the graduated cylinder depicted in Figure 1 are clearly indicated and may be read with certainty. Because all graduated glassware is read with a single approximated digit, this measurement is accurate to the closest 0.1 mL, with an accepted uncertainty of +-0.1 mL.
A more precise method for determining volume is the water displacement technique. This method is based on the fact that water molecules occupy about 1 kiloliter (kL) per kilogram (kg). Thus by measuring the weight of some known volume of water and then repeating the same process with the sample, the amount of liquid present can be determined with great accuracy.
For example, if it is found that 1 kL of water weighs 100 grams (g), then any additional volume of water will weigh 100 g as well. If it is further found that 2 kL of water displace 150 ml (mL) of oil, then any additional volume of water will also displace 150 ml of oil.
Because light particles such as air cells do not affect the reading of a hydrometer, this device is very useful in measuring the density of liquids that would otherwise cloud or foam up when agitated. For example, it can be used to measure the relative densities of oils and waters at different temperatures. The temperature effect can be eliminated by expressing both values as a percentage of the density of water at a given temperature.
There are frequently tiny markers called "graduations" in between the bigger units. To the nearest tenth of a milliliter, read the graduated cylinder (46.5 mL or 20.0 mL). Note that this is the exact volume of one of the test tubes used to measure the blood samples by syringe.
This is important because it means that one drop of blood from a human being contains exactly 0.05 mL of blood.
The reason why this is important is because most chemical tests for blood require a specific volume. For example, a white blood cell count requires that a certain number of cells be obtained by spinning down the whole blood sample and then counting them under the microscope. If your measurement was not accurate enough, some people would get a lot more white blood cells than others when given a blood test!
In general, a small volume of liquid is needed for testing, especially if many samples are being done at once. This is because the tests usually require a specific amount of time or reagent solution, and if too much blood is taken at once it is difficult to accurately divide it up into the required amounts.
People's blood volumes vary a lot, so there is no way that you can take just one drop of blood and have it be sufficient for all tests.
A graded cylinder is intended to be read with the liquid's surface at eye level, with the measuring line visible in the middle of the meniscus. Graduated cylinders typically have capacities ranging from 10 mL to 1000 mL. They are usually made of glass or plastic and should be handled carefully to avoid breaking them.
The term "cylinder" is used for both round and flat objects; however, when talking about measurements, only rounded objects are considered. The word "radius" is often used instead of "diameter," but again, only rounded objects will have a radius. A circle has exactly two radii (the longest distance between any two points on the circle), so every circle has a diameter. A sphere has no length or width; therefore, it has an area. This area is always equal and can be calculated by multiplying the square root of its weight in meters per square meter.
For example, if a sphere weighs 200 grams (7 ounces), then its area is: 21.5 cm2 (19 mm x 9.3 mm).
Cylinders are usually measured along their height or their depth. The volume of a cylinder is easy to calculate if you know the length, height, and radius of the cylinder. For example, the volume of a 20-mL graduated cylinder is 20 *.07 m3 = 0.14 m3.
Scales and precision. The capacity on graduated cylinders is shown on scales with three significant digits for accuracy: 100mL cylinders have 1mL grading divisions, whereas 10mL cylinders have 0.1 mL grading divisions. Of course, you can't really get accurate measurements this way, but it gives an idea of the scale resolution.
There are two main types of scales used in chemistry labs to measure liquid volumes: mechanical and electronic. Mechanical scales are the most economical type of volume scale because they use a pointer attached to a rotating disk or drum to indicate the weight of the container below it. Electronic scales use transducers (similar to microphones) that detect changes in capacitance to determine the weight of the container. These sensors are more accurate than pointers, but they are also more expensive. Electronic scales are generally used where high accuracy is required.
Mechanical scales have two main disadvantages when measuring small volumes: first, their resolution decreases as they get larger (this is not a problem for lab scales), and second, if any substance other than water weighs anything close to the sample being measured, the scale will not work properly. For example, if you were to measure the volume of gasoline using a mechanical scale, there is a good chance that the reading would be inaccurate because most mechanical scales can only measure down to about 5 ounces (150 milliliters).
Because of the cylinder's measuring method, the most precise of the measurements that could be taken here is lowered to 1 mL. The resulting error would be one-tenth of the lowest figure. For example, if a reading is taken and the estimated value is set to 36.5 mL, then the actual volume would more likely be 35.8 or 37.7 mL.
In practice, however, such precision is not possible due to the nature of chemical reactions. Rather than estimating the volume, it is more useful to report the percentage of alcohol by volume (abv). This can be done by dividing the estimated volume by 10 and multiplying by 100; for example, if the estimate was 360 mL, then the abv would be 36%.
It is important to remember that because of errors involved in taking readings from a graduated cylinder as well as calculating volume estimates, there will be some degree of inaccuracy in your results. Do not use a reading from a graduated cylinder to calculate volume estimates or pour recipes without first checking them with other methods.
The common rule of thumb is that you can estimate one extra digit past the measurement device's smallest division. The smallest gradation on a 10mL graduated cylinder, for example, is a tenth of a milliliter (0.1mL). That implies you can estimate the volume to the hundredths of a milliliter when you read it (0.01 mL). A similar rule applies to other common measurement devices including 5-mL test tubes and 1-gallon buckets.
Other methods for estimating volume include using a measuring spoon to measure out an equivalent number of teaspoons or tablespoons of liquid, then multiplying that by the product of the spoon's diameter and its depth. For example, if a spoon measures 1 teaspoon (5 mL) then your volume would be 50 mL. Or you could use a scale to measure out 0.05 g of powder in a small bowl or jar and then multiply that by the density of salt (0.9 g/mL) to get an approximate volume. Always be sure to write down what you add up and how you arrived at your number so you don't overestimate or underestimate your result.
There are two main types of measurements used in chemistry labs: mass measurements and volume measurements. Mass measurements are based on the weight of some object before and after it goes into solution. Volume measurements are based on the size of the container being used. As long as you follow proper protocol it doesn't matter which type of measurement you use because both yield the same result.