Card 0 of 1778
Put the following in order of INCREASING acid strength: H2Se, KH, AsH3, HBr.
Acid strength increases going across a period.
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What is the pH of a solution that has \[OH-\] 1 X 10–4 M?
pOH would be 4 (use –log \[OH–\]) and pH would be 14–pOH = 14 – 4 = 10
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What is the pH of a solution with \[OH-\] = 4 X 10-6
\[OH-\] = 4 X 10-6
pOH = 5.4 — use –log \[OH–\] to find pOH
pH = 14– pOH = 8.6
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Which of the following will produce the solution with the lowest pH?
NaOH is a base, so that won't produce an acidic solution. Of the remaining acids, HCl and HI are strong acids, and HF is weak. HI is at a higher molarity, so it will produce the most acidic solution.
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In the following equation, which is the conjugate base of HClO4?
HClO4 + H2O → ClO4– + H3O+
The conjugate base of an acid will be the same compound, short one H atom. ClO4– is the only one that meets this criterion.
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Which of the following is a Lewis base?
A Lewis base is an electron-pair donor. Only PH3 has a pair of nonbonding electrons and can act as a donor.
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Which of the following is the conjugate base of oxalic acid (H2C2O4)?
The conjugate base has one less H atoms and one unit greater negative charge because of this. Thus, the correct answer is HC2O4–
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Which of the following is a strong acid?
This question is simply testing your memorization of strong and weak acids. Of the list, you should recognize that nitric acid is the only strong acid, and the rest of the choices are weak.
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Put the following acids in order of their INCREASING acid strength: HCl, HS, HBr, H2Se.
Acid strength increases from left to right across a period and increases going down a group.
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Which of the following would best buffer a solution from a pH of 4 to 6?
A weak acid/base best buffers about 1 pH point above and below its pKa. The pKA closest to the middle of 4 and 6 (so want as close to 5) is acetic acid at 4.7.
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A buffer using acetic acid (pKa=4.76) is titrated with NaOH. What is the pH at half the equivalence point?
The pH at half the equivalence point is equal to the pKa of the acid.
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Which of the following solutions has the greatest buffering capacity?
Nitric Acid is a strong acid and can't buffer. Rubidium Hydroxide is a strong base and thus can't buffer. Of the remaining, both are weak acids, but the one with a greater concentration has a greater buffering capacity.
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To create a buffer solution, you can use a weak acid and .
The definition of a buffer solution is that it contains a weak acid and its conjugate base, or a weak base and its conjugate acid. Since we are starting with a weak acid in this case, we need its conjugate base.
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Which of the following can be used in a buffer solution?
For a buffer solution, you need a weak acid and its conjugate base, or a weak base and its conjugate acid. HCO3 from the NaHCO3 and CO3– from K2CO3 are this pair.
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Which of the following will increase the pH of an buffer solution?
I. Removing carbonic acid
II. Adding sodium bicarbonate
To answer this question we need to look at the reaction below:
An increase in the pH will result in a decrease in the concentration of hydrogen ions (). Using Le Chatelier’s principle we can find out which answer choices will decrease
.
Removing carbonic acid will decrease the concentration of . To maintain equilibrium, the reaction will shift to the left and make more reactants from products; therefore, there will be a decrease in the
and an increase in pH.
Recall that salts like sodium bicarbonate, or , will dissociate in water and form ions. Sodium bicarbonate will form sodium (
) and bicarbonate (
) ions. This side reaction will result in an increase in the bicarbonate ion concentration. Le Chatelier’s principle will shift the equilibrium of the given reaction to the left and, therefore, decrease the
. Adding sodium bicarbonate will increase the pH.
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Put the following acids in order of their DECREASING acid strength: HOCl, HOBr, HOI, H2O.
Acid strength of an oxy acid increases with increasing electronegativity on the halogen.
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Put the following acids in order of their DECREASING acid strength: HOCl, HO2Cl, HO3Cl, HO4Cl.
For an oxyacid, the acid strength increases as the number of oxygens increase.
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Which of the following combinations cannot be used to produce a buffer solution?
Buffer solutions can be made via two methods. The first method involves adding equal amounts of a weak acid and a salt of its weak conjugate base (or vice versa). The second methods involves adding a weak acid and a half equivalent of a strong base (or vice versa).
is a weak acid and
is a salt of its weak conjugate base; therefore, this can form a buffer.
is a weak base and
is a salt of its weak conjugate acid; this can also form a buffer. Note that this is the converse of the first method (weak base with salt of weak acid), but it can still form a buffer solution.
is a strong acid and
is a weak base; therefore, adding
and a half equivalent of
will create a buffer solution. This is the converse of the second method (adding a weak base to a half equivalent of strong acid).
and
are both strong reagents (acid and base, respectively); therefore, they cannot form a buffer solution.
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Blood is a physiological buffer. The carbonic acid/bicarbonate system maintains blood’s pH at around 7.35. Carbon dioxide in blood undergoes a complex equilibrium reaction as follows:
Alterations to carbon dioxide levels can change the blood pH.
A patient has abnormally low levels of carbon dioxide in the blood. What can you conclude about this patient?
The question states that the patient has low levels of carbon dioxide. If we look at the given reaction, we will notice that the reaction will compensate for this by shifting the reaction equilibrium to the left. This phenomenon is called Le Chatelier’s principle and occurs to maintain the equilibrium of the reaction; therefore, the reaction will create more carbon dioxide by utilizing bicarbonate and hydrogen ions in the blood. A decrease in hydrogen ion concentration in blood will increase the pH and cause alkalosis (basicity in the blood). Since carbon dioxide is the cause of alkalosis, this patient will experience respiratory alkalosis. If he experienced alkalosis due to a change in bicarbonate ion concentration, the patient will have metabolic alkalosis.
The ratio of carbonic acid to bicarbonate will stay the same because both will be used in equal amounts (1:1 ratio) to produce carbon dioxide. Increasing respiratory rate, or hyperventilation, will result in an increase in the amount of carbon dioxide expelled by the patient; this will decrease the carbon dioxide concentration in the blood and will worsen the respiratory alkalosis. Recall that we are utilizing the bicarbonate ion (in conjunction with hydrogen ions) to create carbonic acid. The carbonic acid will be further broken down to replenish the carbon dioxide. A decrease in the bicarbonate concentration will slow down this process.
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A researcher is trying to make a buffer solution from a weak acid and its weak conjugate base. The pKa of the acid is 5.9 and the desired pH of the buffer solution is 3.5. Which of the following is the best way to make this buffer solution?
One way to make a buffer is by adding equal amounts of a weak acid to its weak conjugate base. For example, you can add 1M acetic acid to 1M acetate to create a buffer solution (note that both acetic acid and its conjugate base (acetate) are weak). However, when using this method you have to remember that the desired pH of the buffer solution has to equal the pKa of the weak acid. The question states that the pKa of the acid is 5.9 and the desired pH of the buffer is 3.5; therefore, it is not possible to make the buffer with the given acid. The researcher would have to find another acid that has a pKa near 3.5.
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