1. Is the origin (0,0) a valid point? Explain. Draw one straight line or several straight lines that best fit the data.

2. How many lines were plotted on your graph? Predict the number of metals that were used in this experiment, and justify your prediction.

3. The formula for a straight line is y = mx + b. What is the value (number reading) of b on your graph? If there is more than one line, do the values of b differ? Since b = , then y = ? .

4. Using a point on the line, not an experimental point, substitute into the amended equation, mass for y and volume for x, and then solve for m, the slope of the line.

5. Identify a physical property equal to the solution for m in Question 4.

6. Draw a perpendicular line on your graph from the 1-mL mark on the x-axis until it intersects the plotted lines. From the point of intersection, draw a line that is perpendicular to the y-axis. What is the density represented by each slope?

7. Use a reference table to determine the densities of the metal samples. Compare these densities to those determined from reading your graph. Decide which density determination is more accurate, and justify your choice.

8. Explain any discrepancies between density as determined from the table and the graph.

9. A liquid sample that occupies 12.6 mL has a mass of 11.2 g. Find the density of the sample.

10. An Aztec amulet claimed to be pure gold weighs 29.03 g in air and 27.43 g in water. Is the amulet pure gold? The density of gold is 19.3 g/cm 3 .

11. In problem 10, if the masses were measured to the nearest tenth of one gram and were 29.0 and 27.4, respectively, does this change the answer?

Implications and Applications

Density, the ratio of mass to volume, is an intensive property. It is often used as a means of checking the identity of a liquid or solid, or checking the concentration of a solution. Jewelry may be checked for its gold content by measuring the density of the specimen. The concentration of antifreeze coolant in an automobile is checked by measuring its density. In many quality control situations, properties are measured and checked to see if the result is within a standard. In some quality control situations, measuring the mass and volume of a sample of product and checking to see if that data pair falls on or near a quality control line is a quality assurance technique.

The amount of a personÕs body fat may be measured by normal weighing and then weighing while submerged under water. Charts are available that correlate body density with percent body fat.

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