Understanding the Density of Water

If you are reading this article, then you are probably wondering what is the density of water?

Usually, it is roughly 1 gram per milliliter. But, keep in mind that a change in the temperature can alter the water density. 

With that, it is given much more importance as compared to water measurement. 

For this guide, we would further discuss water density, why it is important, as well as other information you should know.

Water Density

Before we look at the density of water, let us first briefly discuss what density is. 

Density is simply the measure of mass per volume. The equation looks like this

d = mv

d = density

m = mass

v = volume

To help you put this equation into perspective, let us take a look at the picture below

If you solve for an object density and the result is greater than 1, then that object would automatically sink in water. 

One of the most popular examples usually used in school is oil and water to explain density.

Oil is less dense than water (below 1) so it is no wonder why it floats on water. 

As we have pointed out before, the temperature can alter the density of water. So when you boil water, it would slightly get lighter.

If you look at the table below, you would see that the weight and density of the water slightly change as temperature changes. 

The water density table below is from metrologia

Ice is denser than water

Even though ice is the solid-state of water, it is less dense than liquid water. 

In the picture above, ice floats in water. 

As we glossed over a few times, water temperature alters the water density. So when the water froze and turns into ice, it becomes denser as compared to when it was in its liquid state. 

How does salinity affect water density?

Salinity is the saltiness of the water.

It affects the density of the water because mass also increases every time you put salt in it. 

By simply referring to the formula we cited before, we can already infer that salinity does affect water salinity. 

d = mv

Based on the equation, any changes in mass or volume would affect the density. 

So every time you put salt in water, you are also adding to its mass, which in turn would alter the water density. 

Water becomes heavier every time you put salt in, and the more salt you put in it, the more saline it becomes. 

Measuring Density

Apart from the equation we cited above, there are other ways to measure density and you can even use tools for convenience and more accurate measuring. 

Hydrometer

A hydrometer measures the density of liquid based on the concept of buoyancy. 

Its measuring principle is quite simple and straightforward. 

You would simply insert the glass body into the sample and it would then float at a certain level due to the mass of the hydrometer itself as well as the buoyancy. 

The depth of flotation would then determine the density of the liquid. 

So if you put a hydrometer in liquid like alcohol, kerosene, or gas, it would then sink deeper because these are low-density liquids. 

Keep in mind that aside from its usual specific gravity values, a hydrometer can also be calibrated to 

• Baume
• Brix
• Alcohol
• API (American Petroleum Institute Index) 

Pycnometers

Another tool that would help you measure the density of a liquid is pycnometers.

A pycnometer is usually made up of glass and a ground stopper. The density is calculated based on this formula Density = (M2 − M1)/Flask Volume.

Keep in mind that most pycnometers are calibrated for use in certain temperatures. With that, measurement is only valid at that certain temperature. 

You would then have to make sure that your sample is always equilibrated to the calibrated temperature of the pycnometer. 

Density chart for different elements

The data below is from Harper College’s website. 

Practice Problems

Using the equation and the information we discussed above, try to answer some of these practice problems from Carleton College’s website. 

Problem 1: You have a rock with a volume of 15cm3 and a mass of 45 g. What is its density?

Problem 2: You have a different rock with a volume of 30cm3 and a mass of 60g. What is its density?

Problem 3: In the above two examples which rock is heavier? Which is lighter?

Problem 4: In the above two examples which rock is more dense? which is less dense?

Problem 5: You decide you want to carry a boulder home from the beach. It is 30 centimeters on each side, and so has a volume of 27,000 cm3. It is made of granite, which has a typical density of 2.8 g/cm3. How much will this boulder weigh?

Problem 6: Rocks are sometimes used along coasts to prevent erosion. If a rock needs to weigh 2,000 kilograms (about 2 tons) in order not to be shifted by waves, how big (what volume) does it need to be? You are using basalt, which has a typical density of 3200 kg/m3

Problem 7: A golden-colored cube is handed to you. The person wants you to buy it for $100, saying that is a gold nugget. You pull out your old geology text and look up gold in the mineral table, and read that its density is 19.3 g/cm3. You measure the cube and find that it is 2 cm on each side, and weighs 40 g. What is its density? Is it gold? Should you buy it?

You can view the answer here

Conclusion

Now that you know and understand what water density is, we highly suggest you conduct some experiments at home so that you can apply and better grasp the things you just learned. 

You can try some simple experiments and observations like mixing oil and water, put ice cubes in warm water, and so on. 

We find that applying and observing the things you just learned helps you better understand and grasp what it truly is.

With that, we hoped we managed to clearly explain what is water density as well as some of the other topics we covered like 

• Water Density
• Ice is denser than water
• How does salinity affect water density?
• Measuring Density
  • Hydrometer
  • Pycnometers
• Practice Problems

We have also discussed a few topics that we thought are relevant for your grade level such as

• 30 60 90 Triangle
• Making Sense of the Electronegativity Chart
• Density of Water
• Converting Celsius to Fahrenheit
• SAT Vocabulary Words

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Todd VanDuzer

Co-Founder & CEO at Student-Tutor

Hello! My name is Todd. I help students design the life of their dreams by ensuring college, scholarship, and career success! I am a former tutor for seven years, $85,000 scholarship recipient, Huffington Post contributor, lead SAT & ACT course developer, host of a career exploration podcast for teens, and have worked with thousands of students and parents to ensure a brighter future for the next generation. I invite you to join my next webinar to learn how to save thousands + set your teenager up for college, scholarship, and career success!

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