Answers exam Chemical Analysis – January 02, 2013
Question 1 [4]
a) (The regression is significant if 0 is outside the 99% confidence interval of the slope.)
The 99% confidence interval of the slope is: 0.9913 ± 3 × 0.06 (= [0.8713; 1.1113])
0 is outside of this interval, so the regression is significant
b) Yes, the new AES contains a systematic error.
The intercept is significantly larger than 0 (so, the new AES will always give a higher response
than the old one).
Question 2 [5]
a) Increase
b) (The real molarity can be found with 95% significance in the 95% confidence interval of the
mean)
The 95% confidence interval of the mean is:
0.0012
0.1992 ± 2 × = 0.1992 ± 0.0012 = [0.1980; 0.2004]
√4
So, we expect to find the real concentration in the interval [0.1980; 0.2004].
c) 5% of all measurements is outside this interval; moreover, the interval is symmetric. Therefore,
the chance is 2.5% that the real concentration is lower than 0.1980.
Question 1 [4]
a) (The regression is significant if 0 is outside the 99% confidence interval of the slope.)
The 99% confidence interval of the slope is: 0.9913 ± 3 × 0.06 (= [0.8713; 1.1113])
0 is outside of this interval, so the regression is significant
b) Yes, the new AES contains a systematic error.
The intercept is significantly larger than 0 (so, the new AES will always give a higher response
than the old one).
Question 2 [5]
a) Increase
b) (The real molarity can be found with 95% significance in the 95% confidence interval of the
mean)
The 95% confidence interval of the mean is:
0.0012
0.1992 ± 2 × = 0.1992 ± 0.0012 = [0.1980; 0.2004]
√4
So, we expect to find the real concentration in the interval [0.1980; 0.2004].
c) 5% of all measurements is outside this interval; moreover, the interval is symmetric. Therefore,
the chance is 2.5% that the real concentration is lower than 0.1980.
