Question

ALREADY POSTED ONCE, ANSWERS WERE WRONG

1. Calculate the concentration of a solution obtained when 15.00 mL of 2.04 E-3 M KMnO4 is measured from a buret into a 50 mL volumetric flask which is then filled to the 50.0 mL graduation mark with distilled water.

2. A graph of absorbance vs. concentration yields a linear standard curve for a set of standard solutions. Use the GRAPHICAL ANALYSIS program to plot the following absorbance (y) vs. concentration (x) data:

Absorbance: Concentratio(M)

0.245 6.00 X E-4

0.196 4.80 X E-4

0.147 3.60 X E-4

0.098 2.40 X E-4

0.049 1.20 X E-4

HINT: The concentration are so tiny that they will show up as zero in the GRAPHICAL ANALYSIS data table unless you change the display from 3 places after the decimal to 3 significant figures. (This can be changed after double-clickin gon the column heading.) What is the SLOPE of the graph?

3. Suppose that an unknown sample is analyzed spectrophotometrically (at the same wavelength as that used for the standard curve measurements) and the absorbance was found to be 0.194. Use the standard curve to determine the concentration of the unknown.

Answer 1

1)

2)

concentration	aborbance
(in M)
0.0006	0.245
0.00048	0.196
0.00036	0.147
0.00024	0.098
0.00012	0.049

STANDARD CALIBRATION CURVE:

3) method 1: we will draw straight line(parallel to x-axis) on the graph corresponding to the absorbance of unknown sample(i.e 0.194) and the point at which this line cuts the linear line of the graph , we will draw a straight line parallel to y-axis, the point at which this line cuts the x-axis, will give the concentration of the unknown sample.

from graph: for absorbance = 0.194 , conc = 4.8 X 10^-4M

method 2: using equation of the graph