Measuring Water’s density as a function of temperature
Learn that the density is dependent on the temperature and that even small changes of density is measurable. The difference in the density of hot and cold water is in the hundred’s place. This seems small. But when you use pennies as your mass that goes into your “boat”, you can see how that is significant since the cold water will hold several more pennies than the hot water.
You can have the students predict the penny difference the hot and cold water holds by calculating the density in units of pennies/cm3.
Water Density as function of temperature.
Temp (C) | Temp (F) | Density (g/cm3) |
---|---|---|
4 | 39.2 | 1.000 |
20 | 68 | 0.9982 |
40 | 104 | 0.9922 |
60 | 140 | 0.9832 |
80 | 176 | 0.9718 |
Density is the ratio of an objects mass divided by it’s volume.
We can measure the density of water indirectly by seeing how many pennies will float (see Aluminum Boats lesson).
If you want to take this lesson up another notch, as the students to predict how many more pennies the cold water holds vs. the hot water.
Cold Water Density Measurement
Hot Water Density Measurement
Density Calculation
You want to measure the weight of 5 pennies to reduce error in teh weight measurement and to increase the sensitivity the scale. If you scale is only accurate to a 10th gram, by measuring 5 pennies you are getting the weight of ONE penny to the accuracy of 50th of a gram (5 x better precision).
Weight of 5 pennies is 13.4g Therefor weight of 1 penny is 2.68 (See higher precision than the scale!) Volume = 383 cm3
If volume is the same and only the temperature changes from 20 to 80 degrees (c) and the boat barely floats.
How many pennies would need to be removed to ensure the boat floats.
Water Temp (F) | Actual Density (g/cm3) | Number of Pennies held | Predicted Density (g/cm3) |
---|---|---|---|
60 F | 0.999 | 142 pennies | .9936 |
140 F | 0.983 | 140 pennies | 0.980 |
Doing the experiment is Elementary to Middle school level.
Density Calculation: Middle school level
Easy: Calculating the Density of the hot water and the cold water straight forward: D=m/v e.g. sum of the weight of the pennies / volume of container
Can be hard the penny prediction. E.G. Knowing the density for hot and cold water predict how many more/less pennies the hot water will hold.
Easy.
Hot water is HOT. Please use care when handling hot water. It can burn you!