In this prelab, all answers should be reported to 3 or 4 significant figures.
Scientific notation format = 2.34E-4. The 'E' must be capitalized."
The prelab questions mirror those that you will be doing at the end of the experiment. Bring your work for this prelab assignment to lab and you will have a much easier time completing the Data Analysis Sheet at the end of the experiment.
When preparing your calibration curve for question 4, use the unrounded numbers from questions 1, 2 and 3. If you use the rounded numbers that you entered in prelab, you may not get the correct slope and intercept.
A student performed the experiment at 25°C as described in the coursepack. This was what the student's data sheet looked like. Solution Mass NaCl (9) Mass water (g) Mass % NaCl Mass of 10.00 mL (9) 1 5.651 30.962 D 10.484 4.439 30.312 12.77 10.399 3.226 29.142 9.967 10.288 1.994 30.068 10.162 6.219 3.828 5 1.181 29.672 10.080 Mass of 10.00 mL of unknown: 10.370 g 1. Determine the concentration (mass % NaCl, %w/w) for solution 1 and enter it in the table. 2. Use the data in the measured "Mass of 10.00 mL" column to calculate the density of each of the five standard solutions, and enter the answer for solution 1 below. Density of solution 1 = g/ml 3. Calculate the density of the unknown solution. This value should be calculated simply by using the experimental data provided above. g/mL
4. Make a calibration curve (graph) of density (y-axis) vs. concentration in mass % (x-axis) for the five standard solutions. Use Goolge Sheets or Excel to determine the equation of the best-fit line. Enter the slope and y-intercept of this line below. Referring to the background section on Determination of the Unknown's Mass Percent at the beginning of the experiment, use the slope, the intercept, and the density of the unknown to calculate its concentration in mass %. You may have to increase the number of digits shown by the equation of the line. Hint: Help with spreadsheets [PDF] W - 1 Slope = g .mL-'.(%) Intercept = Mass % unknown= %w/w