It is usually easy to find the mass and volume of different solids and liquids. To find the mass of a solid, just place it on the scale.

Finding the mass of a liquid is a little trickier. First find the mass of an empty container that will hold the liquid. Then fill the container with the designated amount of liquid and weigh it on the scale. The last step is to subtract the mass of the empty container from the mass of the container with the liquid. The difference is the mass of the liquid!

Finding volume requires a different set of techniques. Pour the volume you want to find into a graduated cylinder or a beaker and read the volume in milliliters (ml).

Measuring the volume of solids is a different process. If the solid in question is a regular square/rectangular shape, then you can find the volume by measuring it's length, width, and height. Multiply those three measurements, and you have found the volume. Make sure that your measurements are in centimeters (cm). This way your volume measurements are AUTOMATICALLY in volume units. In other words, one cubic centimeter (cm3) is the SAME as one milliliter (mL), which is the unit of measure displayed on graduated cylinders and beakers. If the solid is an irregular shape, the volume displacement method needs to be used. Use a beaker or graduated cylinder that can hold the solid. Put a specific amount of water into the container and record this volume. Next place the solid to be measured into the container and measure and record the volume of the water/solid combination. Subtract the original volume from the combined volume and the difference is the volume of the solid.

But how do you measure the volume of a gas? How do you measure the mass of a gas? Does a gas like air have enough mass to measure in the lab? Does air weigh anything? It must weigh something, since it IS matter, and matter has both volume AND mass.

This activity will give you a way to estimate the mass and volume of a gas like air. What kind of container can we use to hold the air? A beaker? A graduated cylinder? It would just leak out, and they are probably already filled with air, so these containers wouldn't work too well. We will use a balloon, since it is made just for this purpose!

Problems: How can you estimate the mass of air? How can you estimate the density of a quantity of air? Will the density measurements change as the amount of air in the balloon increases?

Hypothesis:

Materials (per group):

• One or two balloons
• Balance or scale with 0.1 g accuracy
• Tape (to keep the balloon on the scale)
• String
• Metric ruler or meter stick
• Calculator
• Pencil or pen, paper, and graph paper

Safety concerns: Be sure to keep all chemical, heat, and glassware safety rules. Remember not to put a stopper into any flask unless given direct instruction by your teacher.

Procedure:

1. Obtain all of your materials.
2. Take a small piece of tape, make a loop with the sticky side out, and place it on the scale tray. Zero your scale or balance with the tape on the tray so that the tape will not be massed.
3. Place a deflated balloon on the scale and find it's mass. Record this mass on your data table.
4. Take the balloon and inflate it with one lung full of air.
5. The volume of a sphere is found using the formula . Use 3.14 for pi. To find the radius of the balloon place it between two rulers so that they just touch the sides of the inflated balloon. Measure the distance from one ruler to the other. This will give you the diameter of the balloon. Divide this in half and you have the radius or r.
Use the formula and record this volume in the data table.
6. Find the mass of the inflated balloon by zeroing the scale and placing the balloon on the tape so that it does not roll off. Record this mass on the data table.
7. Repeat the steps for finding the mass and volume of the balloon with 2 and 3 lung's worth of air.
8. Repeat the measurements and calculations, recording the data in the table as you go.
9. Calculate the density of each set of measurements. The formula for density is: . Take the mass of each measurement and divide it by the volume for that measurement. This will give you the density of the balloon and air in g/cm3. Record these densities in the data table.

Data:

 Balloon Breaths mass (g) circumference (cm) volume (cm3 or mL) density (g/cm3 or mL) 0 __________ g ____________ cm ____________ cm3 ____________ g/cm3 1 __________ g ____________ cm ____________ cm3 ____________ g/cm3 2 __________ g ____________ cm ____________ cm3 ____________ g/cm3 3 __________ g ____________ cm ____________ cm3 ____________ g/cm3

Analysis:

1. Did the weight of the balloon change as you put more and more air in it?
2. How much did each of your breathes weigh (one breath vs. two breaths vs. three breaths)?
3. Make a graph of two of the following:
• number of breaths vs. mass
• number of breaths vs. circumference
• number of breaths vs. volume
• number of breaths vs. density
4. What shape is the line that each graph makes? Are they straight lines rising to the right, straight lines falling to the right, or curved?
5. Does the mass of the balloon affect your density measurements? Could you change your measurements to adjust for this?
6. Does the balloon compress the air inside? If so, would that make the density of the air increase or decrease?
Review science safety rules here.

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