Introducing KNOVA — A free reading app with curriculum-aligned passages on History & Science for Grades 3-8Learn More →

Using Density to Identify Substances — Reading Comprehension

No ratings yet

Premium Resource

Grades

Standards

MS-PS1-1
MS-PS1-2

Rate this resource

Send Feedback / Report an Issue

About This Reader

This engaging science passage explores how density acts as a 'fingerprint' property, helping scientists and students identify unknown substances. Aligned with NGSS standards MS-PS1-1 and MS-PS1-2, the text explains the mechanism of density, discusses real-world applications like detecting counterfeit coins, and shows how density is used in forensic science and laboratory experiments. The passage includes a glossary, Spanish translation, differentiated version, and multiple graphic organizers. Activities such as quizzes and writing prompts reinforce scientific thinking, while audio integration supports diverse learners. This comprehensive resource supports middle school science learning while connecting density to larger concepts in physical science and materials identification.

CONTENT PREVIEW

Cork floats, wood sinks partially, metal sinks fully in water. — Comparing object densities using water displacement and formula triangle.

Density is a fundamental property that scientists use to identify unknown substances. The amount of mass packed into a certain volume determines the density of a material. For example, a gold coin and a fake coin may look very similar, but their densities can reveal which is real. This makes density a reliable 'fingerprint' for different materials. Understanding how to measure and use density is important in science, industry, and even law enforcement.

How Density Works: The Science Behind the Numbers
Density is calculated by dividing mass by volume, using the equation: Density = Mass ÷ Volume. The unit for density is often grams per cubic centimeter (g/cm³) or kilograms per liter (kg/L). If two objects have the same volume but different masses, the one with more mass has a higher density. For instance, lead has a density of about 11.34 g/cm³, while aluminum is only about 2.70 g/cm³. Scientists measure mass with a balance and volume by either measuring dimensions or using water displacement. When a substance is placed in water, the amount of water it moves equals its volume. This method is especially helpful for irregularly shaped objects.

Real-World Applications: From Coins to Crime Labs
Density plays a key role in many real-world situations. Jewelers use density to identify precious metals and detect fake gold or silver. In forensics, investigators may test the density of unknown powders or liquids to help solve crimes. For example, if a white powder is found at a scene, measuring its density can help determine if it matches a known drug or household substance. Industries also use density to ensure product quality and safety. For example, fuel companies check gasoline density to prevent contamination.

Complexities and Exceptions
While density is a useful identifying property, it is not always perfect. Some substances can have similar densities but be entirely different materials, so scientists often use density alongside other tests, such as melting point or chemical reactivity. Temperature can also affect density because most substances expand when heated, making their density decrease. This is why hot air balloons rise—warm air inside the balloon is less dense than the cooler air outside.

In summary, density is a powerful tool for identifying substances, providing valuable information in science, technology, and crime solving. By combining measurements with scientific reasoning, density helps us uncover the identity and properties of materials in our world.

Interesting Fact: The element osmium is the densest naturally occurring substance on Earth, with a density of about 22.59 g/cm³—almost twice as dense as lead!

What is density?

The amount of mass in a given volumeThe temperature at which a solid meltsThe amount of water an object displacesThe color of a substance

Why is density called a 'fingerprint' property?

Because it is unique for each materialBecause it changes with colorBecause it can be erasedBecause it is only used in crime labs

What is the equation for density?

Density = Mass ÷ VolumeDensity = Volume × MassDensity = Mass × TemperatureDensity = Mass + Volume

Which of the following is a unit for density?

Grams per cubic centimeter (g/cm³)Meters per second (m/s)Kilograms (kg)Liters (L)

What does 'water displacement' help scientists measure?

The volume of irregular objectsThe color of a liquidThe melting point of metalsThe temperature of water

In the passage, which profession uses density to check for fake gold?

JewelersDoctorsTeachersFarmers

According to the passage, why do hot air balloons rise?

Warm air inside is less dense than cool air outsideHot air is heavier than cold airBalloons are made of special materialsThey are filled with water vapor

Why might density alone not be enough to identify a substance?

Some substances have similar densitiesDensity cannot be measuredDensity changes colorAll substances have the same density

True or False: Temperature does not affect density.

TrueFalse

True or False: Osmium is less dense than lead.

TrueFalse