Note: the wording of student responses may vary greatly from the answers given here.

1. a. What is the law of conservation of mass? (8 points)

   The law of conservation of mass states that mass is always preserved in chemical reactions. The mass of the reactants will always equal the mass of the products.

   b. Who developed it? (4 points)

   This law was first stated by Antoine-Laurent Lavoisier.

   c. Describe the experiments this person carried out that led to the law's formulation.
   (8 points)

   Lavoisier heated reacted mercury and oxygen to form a compound. He measured the amount of oxygen used, and the amount of mercury used. The mass of the product was shown to be equal to the mass of the reactants. He then carried out the reverse reaction, decomposing the compound into mercury and oxygen, the mass remained unchanged still.

   d. Which of Dalton's four principles does it support, and how does it support it?
   (8 points)

   This experiment supports the principle that atoms are neither created nor destroyed in chemical reactions.

2. a. What is the law of definite proportions? (8 points)

   This law states that elements combine is fixed mass ratios to form compounds.

   b. Who developed it? (4 points)

   This law was developed by Joseph-Louis Proust.

   c. Describe the experiments this person carried out that led to the law's formulation.
   (8 points)

   Proust decomposed many samples of copper carbonate and each time he obtained copper, oxygen, and carbon in the same mass proportions, 5.3 parts copper, 4 parts oxygen, and 1 part carbon. Experiments on other compounds produced similar results.

3. a. What is the law of multiple proportions? (8 points)

   This law states that two elements may combine in more than one specific ratio, forming different compounds.

   b. How is it different from the law of definite proportions? (8 points)

   This law allows two elements to combine in more than one specific ratio, and allows two elements to form more than one compound. But when two elements can form more than one compound, each compound contains the two elements in a specific mass ratio.

   c. Who developed it? (4 points)

   This law was developed my John Dalton.

   d. What experimental evidence led to the law's formulation?
   (8 points)

   Carbon and oxygen were shown to combine in two proportions to form two distinct compounds. If 4 parts oxygen were combined with 3 parts carbon, carbon monoxide would be produced. If 8 parts oxygen were combined with 3 parts carbon, carbon dioxide would be produced.

   e. Which of Dalton's four principles does it support, and how does it support it?
   (8 points)

   This law supports the principle that atoms of different elements combine in whole number ratios, with more than one ratio being possible for a given combination of elements.

4. 1 g of hydrogen will react with 19 g of fluorine to form HF. By contrast, 1 g of hydrogen will react with 80 g of bromine to form HBr.

   a. How many grams of each product will form in each reaction? (4 points)

   20 g of HF and 81 g of HBr will be formed.

   b. Why are different masses of each element required to react with the same
   amount of hydrogen? (4 points)

   Atoms combine in whole number ratios, and a bromine atom and a fluorine atom have different masses.

   c. Which of Dalton's four principles does this observation support, and how does
   it support it? (8 points)

   This observation supports Dalton's proposition that each element is made of a different kind of atom, and the atoms of different elements have different masses. The differing masses of bromine and fluorine required in each reaction suggest the two halogens have differing atomic masses.

Hill, John W. and Kolb, Doris K. Chemistry for Changing Times, 9th ed. Upper Saddle River, NJ: Prentice Hall, 1998, pp. 37-48.