# Solution Concentration Calculations

I.Solution Preparation

A.For this experiment, you must calculate the mass of solute, nickel (II) nitrate, needed to prepare the four following standard solutions:

1.0.050 M Ni(NO3) 2in a 100 mL volumetric flask.

2.0.100 M Ni(NO3) 2in a 100 mL volumetric flask.

3.0.150 M Ni(NO3) 2in a 100 mL volumetric flask.

4.0.200 M Ni(NO3) 2in a 100 mL volumetric flask.

B.Prepare an Excel® spreadsheet with the following headings:

1.Solution Concentration

2.Mass of Solute Needed

3.Absorption at 400 nm, trial number 1

4.Absorption at 400 nm, trial number 2

5.Absorption at 400 nm, trial number 3

6.Average Absorption at 400 nm

C.Enter the data for Solution Concentration and Mass of Solute for the blank and each of the four nickel (II) nitrate solutions.

II.Preparation of the Calibration Curve

A.A technician has run three trials and has obtained absorbance readings for each of the solutions.

B.The technician's results are as follows:

1.For the blank, 0.000 M Ni(NO3) 2, the results for Absorbance are: 0.00, 0.00 and 0.00.

2.For the 0.050 M Ni(NO3) 2 solution, the results for Absorbance are: 0.23, 0.24, and 0.26.

3.For the 0.100 M Ni(NO3) 2 solution, the results for Absorbance are: 0.50, 0.49, and 0.49.

4.For the 0.150 M Ni(NO3) 2 solution, the results for Absorbance are: 0.75, 0.75, and 0.74.

5.For the 0.200 M Ni(NO3) 2 solution, the results for Absorbance are: 1.03, 0.99, and 1.00.

C.Record each of these values in the appropriate cell of your Excel® file.

D.Calculate the average Absorbance, record them in the appropriate cells of your Excel® file, and use these values for the Absorbance points on your graph.

E.Use the chart function of Excel® to plot an XY (scatter) diagram comparing Absorbance to concentration (molarity).

F.Plot your results with the independent variable, molarity of the nickel solution, along the abscissa, or x-axis, and with the dependent variable, Absorbance, along the ordinate, or y-axis.Move the columns of you Excel® chart as needed to obtain the correct plot; you may use additional "sheets" if you wish to accomplish this.

G.Print a copy of the graph.

H.On your print copy, use a straightedge to draw the best straight line through the points.Do not "connect the dots."The line does not need to touch each point; it should be the most representative straight line so that there will be about the same number of dots above as below the line and at reasonably the same distance from the line.

III.Determination of Nickel

A.The technician, using a nickel (II) nitrate, Ni(NO3)2, solution of unknown concentration, has run three trials and has obtained the following Absorbance readings:0.42, 0.38, and 0.41.

B.Record these results in your Excel® file with the average Absorbance of these results.

C.Calculate the average absorbance and use this value for an absorbance point on your graph. Use the printed graph from above, find the average Absorbance of the unknown on the y-axis, and place a point on the straight line at that Absorbance.

D.Using the observed absorbance and your calibration curve, determine the molarity, or moles per liter, of the nickel (II) nitrate, Ni(NO3) 2, unknown solution. Again use the printed graph; find the point on the x-axis directly below the point on the straight line that represents the Absorbance of the unknown. This is the molarity of the unknown nickel (II) nitrate solution.

E.Enter this information into your Excel® file.

F.Calculate the mass of nickel (II) nitrate that would be found in 100 mL of the unknown solution and enter it into your Excel® file.

G.Plot a second graph with the independent variable, molarity of the nickel solution, along the abscissa, or x-axis, and with the dependent variable, Absorbance, along the ordinate, or y-axis.This graph will include the point for the unknown nickel (II) nitrate solution.

H.Review your graph to ensure that you have included the appropriate labels:Chart Title, the value that the x-axis represents, and the value that the y-axis represents.

1.Show your calculations determining the mass of nickel (II) nitrate required to prepare 100 mL of each of the four standard solutions.

2.Include your Excel graph showing your standard calibration curve.

3.Include your final Excel graph showing the unknown in its proper place on the calibration curve.

4.Show your calculation of the mass of nickel (II) nitrate that would be found in 100 mL of the unknown solution.

#### Solution Summary

Solution concentration calculations are examined.