Question

Unsure why some answers are wrong. Thanks.

This question requires the use of a spread sheet (Excel) to calculate the LINEST uncertainty in the Linear Least Squares best fit line, and the associated unknown sample. You'll be reproducing the calculations in Figure 4-13 in the 7th Addition of Harris. The instructions for using LINEST are on the previous page. Here are mass spectrometric signals for methane in H2 CH4 (vol %): | 0 10.062 | 0.122 | 0.245 0.465 0.971 | 1.921 Signal (mV) 9.1 47.5 95.6 193.8 387.5 812.5 1671.9 Construct a calibration curve: (a) Subtract the blank value (9.1) from all other values (this means that your first data point will be 0,0). Then use the LINEST calculation of least squares to find the slope and intercept and their uncertainties. slope 869.134871310.64216032 intercept -12.98520786 X 8.947402674 (b) Replicate measurements of an unknown gave 152.1, 155.0, 153.9, and 155.5 mV, and a blank gave 9.1, 9.4, 10.6, and 9.1 mV. Subtract the average blank from the average unknown to find the average corrected signal for the unknown. の144.5 (c) Find the concentration of the unknown and its uncertainty. 0.181283956 0.013714159 vol%

Answer 1

1800, 1600 y = a + bºx No Weighting 3714.74445 Equation Weight Residual Sum of Squares Pearson's r Adj. R-Square 1400 0.99915 0.99796 Intercept Slope Value -26.69897 869.73806 Standard Error 13.50933 16.06818 Signal (mv) 200 _ 0.5 1.0 1.5 2.0 CH, (Vol %)

On plotting the graph the slope value obtained was 869.73806 $\pm$ 16.06818

intercept obtained was -26.69897 $\pm$ 13.50933

(b) The average unknown signal given is 144.5

(c) The concentration of the unknown and its uncertainity were 0.19806 $\pm$ 0.01371