# Graphical Method for Calculating Density

Graphical Method for Calculating Density

I. Purpose

To graphically determine the density of two different substances. Class data will be used so as to include multiple trials.

II. Safety

Lab Safety Coats

-It will help prevent chemicals or etc. from getting on your clothes Goggles

-It will help protect your eyes from anything getting into your eyes

III. Pre lab Questions

1. Calculate the slope of the line in the graph above. Use rise over run method. If you don’t know how, ask a friend or look it up. Clearly show your work for the calculation and include units in your answer. Y2-Y1 3.15 grams - 2.10 grams 1.50 grams

--------- = ------------ = -------- = 3 grams/mL X2-X1 1.5 mL -1 mL .5 mL

2. The slope of this line represents the _Density_ of the substance.

IV. Procedures

Get the samples of lead and brass. Also the samples must be clean and dry. Measure the mass of the empty beaker, and then add your lead carefully into your beaker carefully. Record your info. Use the displacement method to find the volume of the lead. Get a graduated cylinder, then fill it up half-full with sink water and record your info. Be very careful when adding your metal sample, try not splashing or losing anything out of the graduated cylinder. If you mess up, start over from step 2 with fresh samples. Also if the water does not cover the metal by now start all over with clean samples. Record your final volume. Repeat steps 2 and 3 for the other metals. Dry both samples.

V. Data and Observations

VI. Calculations

VII. Postlab Questions

1. What does this experiment demonstrate about the density of a substance?

This experiment showed us that we could use balances, the water displacement method, and a graduated cylinder to find the density of Iron and Aluminum. This doesn’t only work for Iron and Aluminum; it could work for any solid(s). 2. Do you think density could help identify an unknown substance? Why?

Yes, I do think that you could find an unknown substance with the density. Only with accurate tools and precision. Also, because the water displacement method would help out a lot and you could find the density of the substance, then look it up on the periodic table or on the internet.

3. Look up the accepted values for the density of Aluminum and Iron. Calculate the percent error by comparing your densities (question 1) to the accepted values. Show all your work.

4. Which of the approaches used in this used in this experiment should be more reliable and accurate; calculating the density from the mass and volume of a single sample, or calculating the density by determining the slope of the graph of the mass and volume data for a number of samples? Explain your answer.

Calculating the density by determining the slope of the graph of the mass and volume data for a number of samples, because once you acquire all that information by doing numerous trials, you can graph the points on the graph. Then you can draw the line of best fit, which will give you more accurate numbers, calculations, and many more.

5. In this lab, did you determine the mean, median, or mode for the density? We did not have to do them in the packets, but we had all the information to acquire that information.

VIII. Conclusion

The purpose of this lab was to find out how to get density and increase our knowledge about density. This lab helped me more on sig figs and also density. It sharpened my knowledge about the water displacement method. I observed how the water was raised and how to find density.

IX. Error Analysis

Well, I already did the percent error in my calculations, but there is one error of analysis. Since we didn’t use actual iron, our percent error was 11.1%. So since we didn’t have iron (but it is still somewhat like iron) we were a little off on our calculations....

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