1) Classify the following as either an element, a compound, a heterogeneous mixture, or a homogeneous mixture. a. A balloon containing nitrogen and oxygen gases berpotens b. A sheet of copper c. Water d. A handful of salt and sand e. Sugar dissolved in water 2) Classify each property as either physical or chemical, a. Water has a boiling point of 100 C. b. Natural gas burns when heated in the presence of oxygen C. A bicycle frame rusts when left outside for some time d. Food coloring mixes when put into water 3) Classify the following components of the scientific method as an observation, a hypothesis, an experiment, a law, or a theory. a. A metal in your hand is silver in color. b. Two objects of different mass are dropped from the height to compare the time each takes to reach the ground. c. All pure substances have definite proportions of their elements. d. If you brush your teeth once a day, you will not develop cavities. Short Answer: answer the following thoroughly and in your own words. 4) What is the key difference between a pure substance and a mixture? 5) What is the key difference between a physical change and a chemical change? 6) What is the difference between a hypothesis, a law, and a theory in the scientific method? 7) Why is it not possible to say that a scientific theory is accurate with 100 % certainty