A teacher asks students to identify which demonstrations show physical changes and which show chemical changes. Which demonstration shows a physical change?
A. Baking soda is mixed with vinegar. The mixture bubbles.
B. A dish of water is placed in the freezer. The water turns solid.
Ο Ο Ο Ο
C. A piece of pH paper is dipped in clear ammonia. The paper turns from yellow to pink.
D. Hydrogen peroxide solution is dropped on a potato slice. The liquid bubbles and fizzes.

While studying chemical reactions and conservation of matter, sarah's class conducted a variety of experiments. sarah and her lab partner found the mass of a wax candle and placed the candle in a flask. the students lit the candle and let it burn to completion. all that was left was wax and charred candle wick. per their teacher's instructions, the students found the mass of the products. their data can be seen in the data table. formulate a hypothesis the students could test to explain why the experiment did not support the law of conservation of matter. a) the students could repeat the experiment using different candles; there might have been a flaw in the candle. b) the experiment should be repeatable. the students should run several trials and then take an average of the after mass in each trial. c) the students should have someone in the class check their measurement skills as they repeat the experiment. they may have made an error using the balance. d) the students should burn the candle in a container that has some type of lid so that any gas that is a product of the reaction can be contained and massed. submit