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Has this ever happened to you? You are baking cookies, and you mistake 1 teaspoon of vanilla for 1 tablespoon. Instead of having some nice cookies with a nice vanilla flavor, they are way too overpowered and not that great tasting. Making measurements is not only an important part of baking, but…
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Jetzt kostenlos anmeldenHas this ever happened to you? You are baking cookies, and you mistake 1 teaspoon of vanilla for 1 tablespoon. Instead of having some nice cookies with a nice vanilla flavor, they are way too overpowered and not that great tasting.
Making measurements is not only an important part of baking, but also of chemistry (and of all sciences). In this article, you will learn how to make good measurements, so you can be on your way to being an awesome chemist! (and baker too!)
When performing any kind of science, you will be making measurements. In chemistry, we often measure things like mass, amount, time, and so on. In this article, we will learn all about how to make good, scientific measurements and why these measurements are so important.
Science is a global phenomenon. All over the world, people are sharing and learning. Because of this, scientists use the International System of Units (SI) (commonly known as the metric system) as a standard, so that measurements are easily identifiable and don't need to be converted to be understood.
There are 7 basic measurements/units under this system, shown in the table below:
Figure 1-Base units of the SI (metric) system | ||
---|---|---|
Measurement | Unit | Symbol |
Length | Meter | m |
Time | Second | s |
Temperature | Kelvin | K |
Mass | Kilogram | kg |
Amount of substance | Mole | mol |
Electric current | Ampere | A |
Light (luminous) intensity | Candela | cd |
There are some other common measurements that you will come across, such as energy (in Joules; J), volume (in Liters; L), and pressure (in atmospheres; atm), but these are considered the main standard units.
One handy thing about the metric system is that it is in base 10. This makes it easier to do calculations with, but also easier to convert between numbered units.
The metric system has a set of prefixes that denote magnitude/scale. Since it is a base 10 system, each prefix/unit is 10x greater or less than its neighbor. These prefixes are often used to "simplify" numbers. For example, 1 kilometers (km) is much easier/nicer than 1000 meters.
Below are the prefixes for units larger than the base unit (100 = 1)
Fig.2-Prefixes larger than base 10 | |||
---|---|---|---|
Name of unit | Symbol | Scientific notation/power of 10 | Numerical form |
deka | da | 101 | 10 |
hecto | h | 102 | 100 |
kilo | k | 103 | 1,000 |
mega | M | 104 | 10,000 |
giga | G | 105 | 100,000 |
tera | T | 106 | 1,000,000 |
Let's test this out using an example:
Convert 10,000 meters to:
a) dekameters
b) kilometers
c) megameters
a) Using our chart, we see that 1 dekameter=10 meters, so:
$$10,000\,m*\frac{1\,dam}{10\,m}=1,000\,dam$$
b) 1 kilometer=1,000 meters
$$10,000\,m*\frac{1\,km}{1,000\,m}=10\,km$$
c) 1 megameter=10,000 meters
$$10,000\,m*\frac{1\,Mm}{10,000\,m}=1\,Mm$$
Now let's look at the units below the base unit:
Fig.3-Prefixes smaller than base unit | |||
---|---|---|---|
Name of unit | Symbol | Scientific notation/Power of ten | Numerical form |
deci | d | 10-1 | 0.1 |
centi | c | 10-2 | 0.01 |
milli | m | 10-3 | 0.001 |
micro | μ | 10-6 | 0.000001 |
nano | n | 10-9 | 0.000000001 |
pico | p | 10-12 | 0.000000000001 |
Like before, let's use this as an example to test your understanding:
Convert 0.00001 seconds to
a) deciseconds b) milliseconds c) nanoseconds
a) Since "deci" is 10-1, that means that it is worth \(\frac{1}{10^1}\) seconds, or to put it another way, every 10 deciseconds is 1 second, so:
$$0.00001\,s*\frac{10\,ds}{1\,s}=0.0001\,ds$$
b) 1000 miliseconds=1 seconds
$$0.00001\,s*\frac{1,000\,ms}{1\,s}=0.01\,ms$$
c) 1,000,000,000 nanoseconds=1 seconds
$$0.00001\,s*\frac{1,000,000,000\,ns}{1\,s}=10,000\,ns$$
While scientists (and most of the world) use the metric system, here in the U.S., we use the Imperial system. Because of this, we might not always be able to make our measurements in the metric system.
For example, when you want to measure the length of something, you might pull out a ruler. Rulers measure in inches (though sometimes they may have a side for centimeters), so it's important to know how to convert between units
Here are some common conversion factors you may need to know:
Length:
Inches to centimeters: 1 inch=2.54 centimeters.
Miles to meters: 1 mile=1,609.34 meters.
Yards to meters: 1 yard=0.9144 meters.
Temperature:
Fahrenheit to Celsius: \((32^\circ F-32)*\frac{5}{9}=^\circ C\).
Celsius to Kelvin \(32^\circ C + 273.15=K\) (Celsius and Kelvin are both used in science, though Kelvin is considered standard).
Mass:
Pounds to kilograms: 1 pound=0.454 kilograms.
When making measurements, there are a few rules we need to follow. The first rule is based on significant figures.
Significant figures (called "sig figs" for short) are the digits in a number that are considered "important" and reliable for indicating the quantity of something.
To put it in simpler terms, significant figures tell us how "sure" we are of a measurement. The more significant figures, the more precise the measurement.
So, what does this have to do with making measurements? Well, let's take a look at a common ruler:
Fig.1-An image of a ruler
The numbers right above the logo are measurements in centimeters. The "notches" in between these numbers each represent 0.1 centimeters.
So let's say I was measuring a piece of metal, it lined up exactly in between the 2 and 3 marks. So, what number should I write down?
a) 2.5 b) 2.50 c) 2.5000
The answer here is b. When making measurements, the last digit is our "estimation digit". Basically, we write down our number based on the number of markings +1. The ruler has markings for centimeters (our first digit) and 0.1 centimeters (our second digit), so we are going to estimate our last digit.
When using electronic devices like a thermometer or mass balance, we use the number given. This estimation is for manual measurements
Another "rule" is for reading the volume of a liquid. When we read the volume of a liquid, we have to measure from the bottom of the meniscus.
The meniscus is the curve near the surface of a liquid caused by surface tension
When measuring volume, you always want to be at eye-level with the meniscus. Looking at a different angle may make the meniscus either harder to see or appear in a slightly different position, which could mess with your measurements.
What is the volume of this liquid?
Fig.2-An example of a meniscus
Looking at the meniscus, we see the bottom of the curve is slightly between the 21 mL mark and the 21.1 mL mark. Because of this, we can estimate that the volume is 21.05 mL.
Our last "rule" is more of a rule of thumb than a set rule. We always want our measurements to be as close to the truth as possible. Because of this, it is common to make multiple measurements and then take the average.
In an experiment, there will always be "random error", which are errors that are hard to account for, such as the humidity of a room causing a sample to weigh more since it absorbed some of the moisture. Other random errors are simple human errors like marking down a number wrong.
Because of this, taking multiple measurements helps account for some errors that may occur.
Now that we've covered the basics of measurement making, let's work on some more examples!
What is the length of the sample?
a) In centimeters b) In millimeters
Fig.3-Measurement of a sample using a ruler
a) Looking at the tip of our sample, we see that it almost, but not quite, reaches the 4.5 cm mark. Because of this, we can estimate that our sample is 4.49 centimeters in length.
b) Since millimeters is the unit below centimeters, 10 millimeters=1 centimeter, so we just need to multiply our answer by 10, so the sample is 44.9 millimeters.
Now for an example using volume:
What is the volume of this sample?
a) 19.80 mL
b) 19.8 mL
c) 20.0 mL
d) 20.00 mL
Fig.4-Volume measurement
Since this is a liquid, we need to focus on the bottom of the meniscus (the dip). The end of the meniscus is right on the 20 mL mark. Since the smallest markings are 0.1 mL marks, then we estimate the next digit. Therefore, our answer is d (20.00 mL).
So, why is taking measurements so important? Well, there are two main reasons: precision and accuracy.
Precision is a measure of how close a set of data points are to each other.
Accuracy is a measure of how close a set of data points are to the true value
Making sure our measurements are precise and accurate is of utmost importance. For example, imagine you worked in a lab synthesizing the key ingredient for a prescription drug. If your mass measurements were off, even by a milligram, it could have disastrous consequences for the people who rely on that drug.
Even when you are doing simple lab experiments, such as determining density, it is good practice to take the best measurements possible, so that when the stakes are raised, your work will be as accurate as possible.
When we "make a measurement" we are using a tool to quantify something based on a variable like time or length
Making measurements helps us quantify and better understand our world. We also make measurements when cooking or doing other tasks
In chemistry, we use several different tools to measure different variables, such as using beakers to measure volume.
An example of making a measurement is using a ruler to measure the length of something
We make measurements to understand the properties of elements and/or compounds. We also use it to synthesize compounds or perform certain tasks
Flashcards in Making Measurements50+
Start learningWhat is accuracy?
Accuracy is a measure of how close measurements are to a target or accepted value
What is precision?
Precision is a measure of how close measurements are to each other
Which of the following is an example of accuracy?
Making a basket in basketball
Which of the following is an example of precision?
Redoing a problem and getting the same answer
What is systematic error?
Systematic error is caused by consistent deviations due to:
-Personal error (such as putting the decimal in the wrong place)
-Methodological error (using wrong method, such as using the solvent)
-Instrumental error (such as being calibrated wrong)
High precision, but low accuracy, is often due to what?
Systematic error
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