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Science · Drill 66

Science practice 66

10 questions ~9 min recommended
⏱ 00:00
Score
—

Key

Summer 2000
Summer 2001--__-
concentration of CH
water table level
140-
aquifer
120
100
groundwater (ppm)
20
0
50
100
150 200 250 300
depth below water table (cm)
concentration of CH, in
groundwater (ppm)
120
100
80
wetland
40
50 100 150 200 250 300 350
depth below water table (cm)

Key

Summer 2000
Summer 2001 ..
aquifer
conductivity of
groundwater (umho/cm)
water table level
900*
800
700
600
500
400
300
0
0
50
100
150
200
250
depth below water table (cm)
300
soil layer
rock layer
pH of groundwater
7
6.
.8
6.
.6
6.
.4
6.
.2
5.8
0
50
100
150
200
250
depth below water table (cm)
300

always win

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Groundwater is water stored beneath the surface of the Earth. Groundwater chemistry in 2 bodies of water—drawn from an aquifer and from beneath a wetland—was studied during a 2000 summer drought and again during the next summer, which had normal rainfall. Figure 1 shows the methane (CH4) gas concentration in the groundwater at various depths in the aquifer and wetland. Figures 2 and 3 show the groundwater conductivity (directly proportional to the concentration of the dissolved ions) and pH at various depths in the aquifer and wetland, respectively. Also shown are the locations of the water table and the depths of the aquifer and wetland below this level.


Figure 1


Figure 2


Figure 3

1. According to Figure 2, the conductivity of aquifer groundwater in 2000 at a depth of 250 cm was closest to which of the following?

2. Based on Figure 2, if the pH of aquifer groundwater at a depth of 260 cm had been measured in the summer of 2001, it would most likely have been closest to which of the following?

3. Which of the following is the most likely explanation for the difference in the depth of wetland groundwater in the 2 years?

4. If the data in Figures 2 and 3 are typical of aquifers and wetlands in general, one would most likely make which of the following conclusions about the soil layer in an aquifer and in a wetland?

5. According to Figure 1, the average concentration of CH4 over the depths of 0 to 300 cm was higher during the summer of:

Polyatomic ions can be represented by the combination of symbols

(XaZb)n

where a is the number of atoms of Element X, b is the number of atoms of Element Z, and n is the total positive or negative charge for the entire polyatomic ion. If a or b is equal to 1, then the number 1 is omitted. If n is equal to 0, indicating a net neutral charge, then the number 0 is also omitted. For example, (NH4)+1 represents an ammonium ion, which contains 1 nitrogen atom (the number 1 is omitted), 4 hydrogen atoms, and a net polyatomic ion charge of +1. Since polyatomic ions carry a charge, they are very soluble in water, as opposed to neutral molecules.

Some atoms that comprise polyatomic ions are able to donate or accept different numbers of electrons, depending on the atoms with which they interact. In these different situations, they are said to have different oxidation states. For instance, while oxygen (O) typically has a constant oxidation state of -2, meaning it typically only accepts 2 extra electrons, chlorine (Cl) can have oxidation states of -1, +1, +3, +5, and +7, meaning that it has the ability to either accept 1 extra electron (-1) or donate either 1, 3, 5, or 7 electrons. The specific ions that feature the different oxidation states of chlorine are listed below.

Table 1
NameIonOxidation state of chlorine atom
Chloride(Cl)−1 −1
Hypochlorite(ClO)−1 +1
Chlorite(ClO2)−1 +3
Chlorate(ClO3)−1 +5
Perchlorate(ClO4)−1 +7

The energy required to remove an electron from an atom, thereby giving that atom a more positive oxidation state, is known as an ionization energy. The ionization energies for removing each of the first four electrons from elements with atomic numbers 11-15, as measured in electron-volts (eV), are shown in Figure 1.


Figure 1

6. Which of the following symbols correctly represents the negatively charged polyatomic ion containing seven oxygen atoms and two chromium (Cr) atoms?

7. According to Table 1, what is the total charge for the polyatomic ion chlorite?

8. Based on Figure 1, the ionization energy required to remove 4 electrons from P (atomic number 15) is approximately twice the ionization energy required for which of the following?

9. A sample of bleach contains a mixture of chlorite and hypochlorite. Based on Table 1 and Figure 1, what is the ionization energy for the chlorine atom in each of these polyatomic ions?

10. Suppose a chloride ion is isolated and accelerated at a constant rate. How would the net force acting on the chloride ion compare with the net force acting on a perchlorate ion that is accelerated at the same constant rate?

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