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Density

Density. Experiment # 3. Density. Glass-to-glass-to-glass transfers. Density of an unknown liquid. Weigh and record the mass of a clean, dry beaker. Rinse graduated cylinder with ~5 mL of unknown liquid. Dispose of the rinse liquid. (It may go down the sink. It is salt water.)

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Density

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  1. Density Experiment # 3

  2. Density

  3. Glass-to-glass-to-glass transfers

  4. Density of an unknown liquid • Weigh and record the mass of a clean, dry beaker. • Rinse graduated cylinder with ~5 mL of unknown liquid. Dispose of the rinse liquid. • (It may go down the sink. It is salt water.) • Fill the graduated cylinder with 40-45 mL of the unknown liquid. • Record the volume of the liquid to the nearest 0.1 mL. • Transfer the liquid to the weighed beaker using glass-to-glass-to-glass method. • Reweigh the beaker. • Pour unknown liquid back into graduated cylinder and repeat with a different volume of unknown liquid

  5. glass-to-glass-to-glass transfer Pour liquids down a glass rod for clean pouring.

  6. Sample Data • Hints: • Put an even number of mL of the liquid into the graduated cylinder. • Make sure that all of the liquid drains into the beaker using glass-to-glass-to-glass method.

  7. Density of an irregular solid • Determine density by displacement of water Add weighed sample of irregular solid – here a rubber stopper Fill graduated cylinder with a known volume of water. Determine total volume of rubber stopper and water.

  8. Sample Data Data, must be in ink!! Calculated value, pencil OK • Hints: • You will be assigned one of five irregular solids. • Start out with 25.0 or 30.0 mL of water • Fill the graduated cylinder to the line with an eyedropper before adding irregular solid. • Remember to keep track of significant figures. • Remember to record your original data in ink! (That doesn’t mean copying it over again later or going over the pencil with a pen!!)

  9. Density of a metal cylinder Add metal cylinder Fill graduated cylinder containing rubber stopper with a known volume of water. (Rubber stopper will act as a shock absorber so you do not break the graduated cylinder). Determine total volume of rubber stopper, metal cylinder and water.

  10. Sample Data • Hint: • Remember to keep the rubber stopper in the graduated cylinder. Many of the metal cylinders are heavy and will break the glass graduated cylinders if they are dropped directly into the water.

  11. Finishing up • Once you have gathered all of the data, enter it onto the spreadsheet at http://www.grossmont.edu/chemistry/oldSite/Resources/120_lab_materials.htm • Either print out the spreadsheet or get me to sign off on your lab sheet. • Answer all of the questions in the lab. Questions and sample calculations may be done in pencil. (Just be sure to record the data in ink!)

  12. Handbook and Graphing Experiment # 5

  13. Handbook and Graphing Lab • Goals for this lab • Learn to find information in the CRC handbook of chemistry and physics • Learn how to draw and use a proper graph.

  14. CRC Handbook • The CRC Handbook contains an abundance of useful information, especially data regarding physical properties of substances • The CRC is republished every year and there are often changes in the way it is organized. The index is a useful tool for finding information. • You will be exploring the CRC in this lab to learn how to find information. • DO NOT write in the CRC!

  15. Graphing • When creating a graph keep the following in mind • Graph must have clearly labeled title and axes. • Use black or blue ink to draw in axes and points on the graph. Pencil may be used for drawing lines to connect points and drawing circles around points. • Some good and bad examples of graphs follow. • Circles can be drawn around points to make them easier to see.

  16. Dependent quantity as a function of independent quantity y axis x axis x axis is independent variable, y axis is dependent variable

  17. Draw axes on graphs and choose reasonable units.

  18. This graph does not use the entire page

  19. Here units make graph hard to interpret.

  20. Graphing examples • Lets look at some examples of graphs

  21. Do not connect the dots. Draw the best straight line through the points.

  22. Much better

  23. This is not a linear relationship. Draw a smooth line through points. Note that units are multiplied by 10-4

  24. Can we change this into a straight line? Try log area vs diameter? No--

  25. Try 1/area vs diameter - no

  26. Try area as a function of diameter squared – Yea! A straight line!!

  27. Now fix the units Note that units are multiplied by 10-3

  28. Often, graphing requires lots of trial and error to discover the relationship between two variables. • This is much easier with graphing calculators and computers, but in the past it was done by hand just as you will do with these graphing exercises. • You will get the chance to try computer graphing on the last exercise.

  29. Due today • Experiment 2 from last week • If you leave early • Experiment #3 • Experiment #5 • Have your lab data stamped before you leave!!

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