5 - PS1A.B. - Matter Changing States - FINAL (WND 1-6-2014)

DCI: PS1.A (B) Structure and Properties of matter – the amount (weight) of matter is conserved when it changes form, even in transitions in which it seems to vanish.

DCI: PS1.B (A) Chemical Reactions – No matter what reaction or change in properties occurs, the total weight of the substances does not change.

 PE: 5-PS1-2  Measure and graph quantities to provide evidence that regardless of the type of change that occurs when heating, cooling, or mixing substances, the total weight of matter is conserved.

[Clarification Statement: Examples of reactions or changes could include phase changes, dissolving, and mixing that form new substances.] [Assessment Boundary: Assessment does not include distinguishing mass and weight.]

These are the ideas we see in the standard: 

-the amount of matter is conserved when it changes form

-the total weight of a substance does not change during a chemical reaction or physical change

There will probably be plenty of examples of melting ice, freezing water, or creating a mixture of some sort.  In all of the examples, the student should have to explain that the amount of matter that was present before the change will equal the amount of matter present after the change.  In cases like dissolving or evaporation, where the matter seems to disappear, they will probably need to offer an explanation. The reverse of that could be true too, in the case of condensation, matter seems to appear from nothing.  

Possible Question Starters:

"A student placed a beaker of water near a window in the classroom and recorded the volume of water once a week for four weeks. 

Which of the following best explains the change in the volume of water in the beaker? 

correct answer - some of the water has changed state

incorrect answer - 

"A beaker of liquid water and ice cubes was placed on a hot plate just long enough for the ice to melt. Which of the following predictions can be made about the mass of the contents of the beaker after the ice melts?"

correct answer - the mass of the beaker will be equal to the mass of the original amount of liquid water plus the mass of the ice cubes

incorrect answer - the mass of the beaker will be more than the original amount of the liquid water plus the mass of the ice cubes