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Determining Density with Accuracy & Precision

Include the following information at the top of the first page of your assignment:

Name:

Lab Section Number:

Experiment Title:

Due Date:

GENERAL INSTRUCTIONS

The entire report should be typed (handwritten portions will NOT be graded). Please organize your report as shown below.

Preliminary Questions:

1. How are mass and volume related? Given a mass measure, how can you calculate the volume that the specific mass of water represents by using the density?

1. Why is it necessary to take the temperature of the water used in this experiment?

1. When measuring the volume to be delivered, where do you read the amount of liquid in the container?

1. You measure the mass of an empty dry beaker at 43.451 g. After delivering a volume of water to the beaker, you re-measure the mass and obtain 58.231 g. Show ALL calculations when answering the following questions. Make sure to report the values to the correct number of significant figures!!!

1. What is the mass of water that was delivered to the beaker?

1. If the liquid density is 1.0156 g/mL, estimate the liquid volume delivered in mL.

1. You had used a graduated cylinder and tried to measure a known volume of 15.0 mL, calculate the error and % relative error for the measurement. Make sure to report your values to the correct number of significant figures.

DATA

Use the data given in the table below for the calculations for parts A-C to answer the questions following data analysis.

Table 1. Raw data measurements using three measurement methods for the determination of water volume. Data reflects the weight (g) of a 50-mL beaker plus 10 mL of water measured using each method. A dry, empty 50-mL beaker with a mass of 50.132 g was used for all measurements. Room temperature was 22.3°C.

 Method 1 Trial 2 3 50-mL beaker 59.981 59.216 60.459 25-mL graduated cylinder 60.08 60.256 59.884 10-mL pipette 60.098 60.132 60.065

CALCULATIONS

Part A:

1. Create a typed table (following the example below) that concisely presents your data from Part A (the 50-mL beaker). Include the water temperature, density of the water, and the dry weight of the beaker in the table caption. Pay attention to significant figures!!!

Table 2. Data for the determination of water volume using a 50-mL beaker. The mass of the dry, empty 50-mL beaker was 50.132 g. Water equilibrated with room temperature

(22.3°C) at which the ρwater = 0.99770 g/mL.

 Trial Mass Beaker + Water (g) Mass of Water (g) Volume of Water (mL) 123

Part B:

1. Create a typed table (following the example in part A) that concisely presents your data from Part B. Include the water temperature, density of the water, and the dry weight of the beaker in the table caption.

Part C:

1. Create a typed table (following the example in part A) that concisely presents your data from Part C. Include the water temperature, density of the water, and the dry weight of the beaker in the table caption.

Summary Parts A –C:

1. Create a typed table that concisely summarizes the five calculated values from parts A-C described below. (These values will represent the columns in your table while the three pieces of glassware are the rows.) Calculate the average, the standard deviation, the percent relative standard deviation (% RSD), the error and the percent relative error for the volume. Assume a known (or expected) volume of 10.00 mL for the error calculations. Report the final values for the standard deviation and %RSD with two significant figures.

1. Show one set of typed sample calculations from part B to find the volume of water, the average volume, the standard deviation, the % RSD, the error, and the % relative error.

Part D:

In part D, you are estimating the density of an unknown liquid. This differs from Parts A-C in which you compared the ability of three different glassware to deliver accurate and precise volumes. However, you will utilize the results from A-C to determine the best method for measuring exactly 10.00 mL of the unknown liquid.

1. Based on the data in the summary table for A-C, which glassware (beaker, graduated cylinder, or pipette) was the best method for accurately and precisely measuring 10 mL of water? Explain why this method may have been more appropriate for measuring the volume of a liquid than the other two (i.e., support your answer with data!).

Given this method, you measure exactly 10.00 mL of the unknown liquid into the dry 50-mL beaker and record the following mass for each of three trials.

Table 3. Raw data measurements for the determination of the density of an unknown liquid. Data reflects the weight (g) of a 50-mL beaker plus 10 mL of liquid measured using [insert best method]. A dry, empty 50-mL beaker with a mass of 50.132 g was used for all measurements. Room temperature was 22.3°C.

 Trial 1 2 3 60.456 60.542 60.560

1. Given exactly 10.00 mL of the liquid, how would you utilize the mass measurement to estimate the liquid density?
2. Create a typed table similar to that below that concisely presents your data from Part D.

Your table should clearly indicate the method chosen for this portion of the experiment.

Table 4. Data for the determination of the density of an unknown liquid. A volume of 10.00 mL was measured using a [insert best glassware] and delivered into a 50-mL beaker with a dry mass of 50.132 g. Liquid equilibrated with room temperature (22.3°C).

 Trial Mass Beaker + Liquid (g) Mass of Liquid (g) Liquid Density (g/mL) 123

1. Calculate the average density, the standard deviation, and the %RSD for your density measure. Given the level of precision, how much confidence would you have in your density prediction?

1. Based on your data from part D, the average density of the unknown is _______ g/mL. The % error is ______%. Is the unknown Diet or Regular Pepsi?

QUESTIONS

1. Suppose that in each case below, you were told to measure the specified volume of a liquid, but were not told what piece of glassware to use. You have the following pieces of equipment available: 10-mL beaker, 50-mL beaker, 10-mL graduated cylinder, 25-mL graduated cylinder, 10-mL volumetric pipet, 15-mL volumetric pipet. Which of these would you choose in each case? If more than one answer is possible, choose the best answer. Give a brief explanation for your choice in each case.

1. 15.00 mL
2. 18 mL
3. Approximately 30 mL – exact volume doesn’t matter

1. Using a 10.00 mL pipette, you perform three measurements to determine the density of an unknown liquid and obtain the following values for the liquid mass in grams:

15.125, 15.687, 14.788

1. Calculate the average liquid density and the standard deviation of the density.

1. Which of the following common solvents might the unknown liquid be: chloroform, carbon tetrachloride, and/or methylene chloride? Support your answer! (Note: your data might not be able to exclude more than one possibility)