Mass & Volume of Water

Our last experiment was looking at mass and volume of water... Groups discussed the different properties of water...and in our discussion, we decided to examine the mass and volume of liquid water compared with frozen.

Most Room 5 "knew" that frozen water was heavier....and it was mixed about the volume.  Most thought the volume would be less in frozen water since it would freeze together...

Learning to use the scales was something new for most of Room 5...

We used gram weights...we had some made of plastic, and some metal ones...  It didn't make any difference because 1 gram is 1 gram! 

We first taped a graduated strip on the side of a 9 oz. clear cup...then poured in 100 mL of cool water.  Once each group was confident it was 100 mL, they measured how much it weighed.

It was tricky for some to get the scale re-balanced with the water on one side and the weights on the other. 

Our measurements of mass varied from 106 grams to 117 grams. 

From that point, each group was to figure out the mass of 1 mL of water. 

Dividing 106, 108, 112, 116, or 117 grams by 100...they were all very close to 1 gram for 1 mL of water.

Because of the discrepency in mass, we talked about 'margin of error'...  this was a little difficult for some Room 5ers to understand...

I know they all enjoyed using the scales, the gram weights, and the experiment in general...

Once they were all weighed, we filled a second 9 oz cup with 100 mL of water, making sure both the cups for each group had the same mass.  The volume was the same, 100 mL.  Group 1 wrote a '1' on both their cups...as did group 2, 3, and 4.  We covered each cup with plastic wrap...

Then we took a journey to the kitchen...and to the freezer.  Into the freezer went one cup from each group.

The freezer!  Room 5 was impressed with the size of it!

Here's our water that we didn't freeze.

Unfortunately, I got so busy with the experiment 2 days later when we looked at the mass and volume of the frozen water and compared it with the liquid, that I forgot to take any pictures!  No one could believe this had happened...including me! 

Our results:  the volume of the frozen water was now 120 mL!  Some said the water 'rose,' some said it 'grew', and a few said it 'expanded'.

The mass was surprising...One group who had their liquid water with a mass of 117 grams, had their frozen water with a mass of 117 grams.

The other groups' mass increased by 1 - 3 grams.  They initially concluded that water was heavier when it was frozen.  Here was the difficult part:  trying to show that one gram difference could easily be a 'margin of error'.  Where could this 'margin of error' come from?   (The measuring strip taped on the side of the cup could be slightly off between cups, for example. The accuracy of having exactly 100 mL in the cup.)

Now...even though the two cups in each group were basically the same mass, the volume was more with the frozen water...

The question:  if we had exactly 100 mL of liquid water, and 100 mL of frozen water, would they have the same mass?  No... ice is lighter because the molecules in water have expanded.  That's why ice floats!  We talked for quite awhile...it was fun watching the light bulbs go on in their minds.  The topic needs some more discussion... it's definitely work in progress!