Question

2. A linear standard curve of KMnO4KMnO4 is prepared from a set of standard solutions by plotting absorbance (y) vs. concentration (x). Use Google Sheets/Excel to plot this standard curve using the data in Table 1.

Table 1: Data for the standard curve of KMnO₄

Absorbance	Concentrations (M)
0.210	6.00E-4
0.168	4.80E-4
0.126	3.60E-4
0.0840	2.40E-4
0.0420	1.2E-4

After plotting the standard curve, enter its slope below (not the equation of the line). Report your answer to 3 significant figures. If your answer ends in one or more zeros, use scientific notation.

Slope =

3. Suppose that an unknown sample is analyzed spectrophotometrically at the same wavelength that was used for the standard curve and the absorbance was found to be 0.199. Use the standard curve to find the concentration of the unknown.

=

Answer 1

From given data we have a graph as follows,

Here x-axis is concentration (M) and y-axis is absorbance.

From above graph we have slope(m) = 350

[we know that slope(m) = y/x

Suppose From given data consider readings x=0.00036 and y= 0.126

Now slope (m) = y/x = 0.126/0.00036 = 350 ]

Also from above graph we have linear equation y=350x [i.e,y=mx]

Given that the absorbance of unknown sample is 0.199

From line equation we have,

Concentration (x) = absorbance(y)/ 350

x = 0.199 / 350 = 0.199/350 = 0.00057

Therefore the concentration of unknown sample at given absorbance 0.199 is 0.00057M