# Environmental Science Chemistry Worksheet

An environmental scientist developed a new analytical method for the determination of cadmium (Cd2+) in mussels. To validate the method, the researcher measured the Cd2+ concentration in standard reference material (SRM) 2976 that is known to contain 0.82±0.16 ppm Cd2+. Five replicate measurements of the SRM were obtained using the new method, giving values of 0.799, 0.761, 0.825, 0.838, and 0.762 ppm Cd2+.

< Attempt 1 Question 4 of 12 An environmental scientist developed a new analytical method for the determination of cadmium (Cd2+) in mussels. To validate the method, the researcher measured the Cd2+ concentration in standard reference material (SRM) 2976 that is known to contain 0.82 + 0.16 ppm Cd2+. Five replicate measurements of the SRM were obtained using the new method, giving values of 0.799, 0.761, 0.825, 0.838, and 0.762 ppm Cd2+. Calculate the mean (C), standard deviation (8x), and the 95% confidence interval. A list of t values can be found in the Student's t table. = 0.03036 Ø ppm 0 Sc= 0.82 ppm 95% confidence interval: + 0.16 ppm Does the new method give a result that differs from the known result of the SRM at the 95% confidence level? yes no < Question 6 of 12 >
Attempt 3
Canadian (g)
U.S. (g)
1
2.349
2.556
2
2.371
2.501
Although the Canadian and U.S. one-cent coins have slightly different
dimensions and alloy compositions, the two types of pennies have
similar masses. The table below lists the masses of individual pennies
from each country measured using the same balance. Compare the
two sets of one-cent coins by determining tcalculated. Refer to the table
of Student’s t values as necessary. Assume that the population
standard deviation (o) for each data set is the same.
3
2.299
2.497
4
2.328
2.561
5
2.361
2.522
6
2.313
2.490
7
2.357
2.541
8
2.333
2.531
9
2.304
2.534
10
2.513
tcalculated =
15.784
Are the masses of the Canadian and U.S. one-cent coins
significantly different at the 98% confidence level?
The difference is not significant.
The difference is significant.
Attempt 3
Question 6 of 12
>
tcalculated =
15.784
Are the masses of the Canadian and U.S. one-cent coins
significantly different at the 98% confidence level?
The difference is not significant.
The difference is significant.
Suppose the number of replicate measurements and the average mass of an individual penny remain the same, but the
standard deviation of each data set is three times greater than its original value. Calculate the t value to compare these two
data sets.
Ø
tcalculated =
5.249
For the second set of measurements, is there a significant
difference in the masses of the two types of coins at the
98% confidence level?
The difference is significant.
The difference is not significant.

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