Chemistry 1025 Environmental Science
Lab Final Exam Review
A number is a significant figure if it is: - ANS a. a nonzero digit 4.5 g 2
122.35.m 5
b. a zero digit between nonzero digits 205 m 3
5.082 kg 4
c. a zero at the end of a decimal number 50. L 2
25.0 oC 3
d. any digit in the coefficient of a number 4.0 x 105 m 2
written in scientific notation
A number is not significant if it is: - ANS a. a zero at the beginning of a decimal number 0.0004
lb 1
0.075 m 2
b. a zero used as a placeholder in a large 850,000 2
number without a decimal point
In regards to significant figures, in multiplication and division, the final answer is written so it has
the same number of digits as the measurement with the fewest significant figures - ANS
Example:
24.65 x 0.67 = 16.5155 17
four SF two SF calculator display final answer rounded to two SF
What is meant by the "Q" value? - ANS Those individual values that are farthest from the mean
are candidates for deletion
(―rejection‖) from the data set. For small data sets (n < 10), a simple method to determine
if an individual value needs to be rejected is the statistical test known as the Q test. In this
test, a value for ―Q‖ is calculated and compared to a table of Q values that represent a
certain percentage of confidence that the proposed rejection is valid. If the calculated Q
value is greater than the value from the table, then the suspect value is rejected and the
mean is recalculated. If the Q value is less than or equal to the value from the table, then
the calculated mean is reported. ―Q‖ is defined as follows:
Q = gap / range
where the ―gap‖ is the difference between the suspect value and its nearest neighbor and
the ―range‖ is the difference between the questionable value and the value furthest from
it.
What is meant by the Average or Mean value? - ANS the sum of the measurements divided by
the number of measurements.
, Is the vertical axis the x or the y axis? - ANS y
is the horizontal axis the x or the y axis? - ANS x
the vertical axis is the ___________? - ANS ordinate (y)
the horizontal axis is the ____________? - ANS abscissa (x)
Name the 5 steps involved in constructing a graph - ANS 1. select the axes. 2)Set the scales for
the axes (they do not have to be the same. 3)Plot the data. 4) Draw a curve for the best fit or
straight line if that's appropriate. 5) Title your graph.
The formula for density is: - ANS mass divided by volume
Clearly define precision and accuracy - ANS Accuracy is how closely the measured values lie to
the true values. Precision is how closely the measured values lie to one another.
Given the following five measurements, apply the Q test (90% confidence level) and decide
whether the suspect value (12.155) can be rejected.
12.036, 12.155, 12.041, 12.012, 12.025 - ANS Q=gap/range
gap =
range =
After carefully measuring the mass and volume of aluminum, a student calculates the density of
aluminum to be 2.95 g/mL. According to the CRC Handbook of Chemistry and Physics, the
density of aluminum is 2.702 g/mL. What is the percent error in the student's measured density?
- ANS percent error = [x-y] / y x 100
x=your measured value
y=the accepted value
In what form do plants and trees generally absorb nitrogen? - ANS nitrate ion
What process converts the nitrogen-containing ion in part a) into the nitrogen-containing ion in
part b)? - ANS nitrification or nitrogen fixation
Describe nitrification - ANS ammonium ions are converted to nitrite ions and then to nitrate ions
by bacteria
What are typical nitrate levels in freshwater? - ANS less than 1 mg/L
Describe at least one ―man-made‖ source of nitrates into the environment. - ANS animal
feedlots, agricultural run-off, treated municipal water being returned to streams, urban runoff
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