Mixing Volumes thinking & using molecular models

Water & Water When 50 mL of clear water and 50 mL of colored water are mixed, volume is CONSERVED: the total is 100 mL. water 50 mL colored water 50 mL 100 mL mix

How can we model this? The water molecules mix evenly together. Because the water molecules are all the same size, they take up the same space mixed or unmixed. Our eyes see less red molecules, so the color is fainter when the waters mix.

Water and Oil When you pour oil into water the volume is CONSERVED (stays the same). The oil and water don’t mix: the oil sits on top of the water.

The water molecules sit below. The oil molecules sit above. How can we model this?

Water and Sand When you add sand to water, the volume is NOT conserved. 50 mL of water + 50 mL of sand will always equal LESS than 100 mL.

+= dry sand waterwet sand & water 50 mL 100 mL 80 mL Some water is in between the sand grains.

The tiny water molecules can fit in between the large sand grains. How can we model this?

Water & Alcohol  When water and alcohol are mixed, volume is NOT CONSERVED.  50 mL water + 50 mL alcohol = 95 mL !  Which model fits better:  equal size molecules mixing?  different size molecules mixing?

Water molecules are slightly smaller than alcohol molecules, so the water fits into some of the space. Alc