Making Measurements

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 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!)

• This article covers making measurements.
• First, we will get a brief into making measurements, then learn about the metric system of measurements.
• Next, we will learn some conversions from the US standard to the metric system.
• Then, we will learn the basic rules of making quality measurements.
• Thereafter, we will work on some examples to apply these rules.
• Lastly, we will summarize why making good measurements is so important.

Making Scientific Measurements

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.

Making Metric Measurements

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:

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)

Let's test this out using an example:

Now let's look at the units below the base unit:

Like before, let's use this as an example to test your understanding:

Conversions

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.

Rules in Making Measurements

When making measurements, there are a few rules we need to follow. The first rule is based on significant figures.

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.

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.

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.

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.

Making Measurement Examples

Now that we've covered the basics of measurement making, let's work on some more examples!

Now for an example using volume:

Importance of accurancy and precision

So, why is taking measurements so important? Well, there are two main reasons: precision and accuracy.

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.