Properties of Matter — Answer Key
Part A: Multiple Choice
Circle the best answer for each question.
1. A student has two blocks that are exactly the same size. Block A has a mass of 30 g and Block B has a mass of 60 g. Which statement is correct?
A) Block A is denser because it weighs less and takes up less space.
B) Block B is denser because it has more mass packed into the same volume.
C) Both blocks have the same density because they are the same size.
D) Density cannot be compared unless both blocks are placed in water.
Since both blocks have the same volume, the one with more mass has a higher density. Block B has 60 g in the same space where Block A has only 30 g, making Block B twice as dense.
2. A layer of oil sits on top of water in a glass, and a marble rests at the bottom. What does this layering tell you about the densities?
A) Oil is densest, then water, then the marble is least dense.
B) The marble is densest, then water, then oil is least dense.
C) Water is densest because it is in the middle of the glass.
D) All three have the same density but different volumes.
Denser substances sink below less dense ones. The marble sinks through everything because it is the densest, water sits in the middle, and oil floats on top because it is the least dense of the three.
3. A sealed balloon is placed in a freezer. After one hour the balloon is smaller. What best explains this change?
A) The gas particles escaped through tiny holes in the balloon material.
B) The gas particles lost energy and moved closer together, reducing the volume.
C) The gas changed into a liquid inside the balloon from the cold temperature.
D) The balloon material shrank because rubber gets smaller in cold air.
Cold temperatures remove thermal energy from gas particles, causing them to slow down and move closer together. This shrinks the volume of the gas inside the balloon, making it appear smaller.
4. Ice floats on liquid water instead of sinking. Which explanation is scientifically accurate?
A) Ice is colder than water so cold things always rise to the top.
B) Ice has a lower density than liquid water because its molecules are arranged in a spread-out structure.
C) Ice floats because it is a solid and all solids float on their own liquids.
D) Ice floats because the air trapped inside the ice makes it lighter.
When water freezes, its molecules lock into a crystal structure that spaces them farther apart than in liquid water. This spread-out arrangement gives ice a lower density, which is why it floats.
Part B: Fill in the Blank
Write the correct answer on each line.
1. When a substance is heated, its particles gain energy and move farther apart, which can lower its density.
Heat gives particles extra kinetic energy, causing them to vibrate and spread farther apart. With the same mass now taking up more space, the substance becomes less dense.
2. A solid keeps its own shape because its particles are locked in fixed positions.
Solid particles are held tightly in fixed positions by strong forces, so the solid does not flow or spread out. That is why a wooden block keeps its shape whether it sits on a table or inside a box.
3. The temperature at which a solid turns into a liquid is called the melting point.
The melting point is the specific temperature where a solid gains enough energy for its particles to break free of their fixed positions and begin flowing as a liquid. For example, ice melts at 0 degrees Celsius.
4. In a gas, particles move in all directions and fill the entire container.
Gas particles have so much energy that they zoom around in every direction, bouncing off each other and the container walls until they spread out to fill all available space.
5. Water is unusual because its solid form is less dense than its liquid form.
Most substances are denser as solids, but water is an exception. Ice crystals have an open, spread-out structure that makes solid water less dense than liquid water, which is why ice floats.