Identify the principle conjugate acid/base pair and calculate the ratio between them in a solution that is buffered to pH 9.00 and contains
a. H2S
b. ethylenediamine dihydrochloride
c. H3AsO4
d. H2CO3
a. The principle conjugate acid/base pair for H2S is H2S/S2-.
To calculate the ratio between them in a solution buffered to pH 9.00, we can use the Henderson-Hasselbalch equation:
pH = pKa + log([A-]/[HA])
In this case, the pKa for H2S is 7.00. Rearranging the equation, we get:
[A-]/[HA] = 10^(pH - pKa)
[A-]/[HA] = 10^(9 - 7) = 100
Therefore, the ratio between S2- and H2S in the buffered solution is 100:1.
b. The principle conjugate acid/base pair for ethylenediamine dihydrochloride is ethylenediamine/Ethylenediamine hydrochloride.
To calculate the ratio between them in a solution buffered to pH 9.00, we again use the Henderson-Hasselbalch equation:
pH = pKa + log([A-]/[HA])
In this case, the pKa for ethylenediamine is pKa = 9.00. Rearranging the equation, we get:
[A-]/[HA] = 10^(pH - pKa) = 10^(9 - 9) = 10^0 = 1
Therefore, the ratio between ethylenediamine and ethylenediamine hydrochloride in the buffered solution is 1:1.
c. The principle conjugate acid/base pair for H3AsO4 is H3AsO4/H2AsO4-.
To calculate the ratio between them in a solution buffered to pH 9.00, we use the Henderson-Hasselbalch equation:
pH = pKa + log([A-]/[HA])
In this case, the pKa for H3AsO4 is pKa = ? (not provided). Without the pKa value, we cannot calculate the ratio between H3AsO4 and H2AsO4-.
d. The principle conjugate acid/base pair for H2CO3 is H2CO3/HCO3-.
To calculate the ratio between them in a solution buffered to pH 9.00, we use the Henderson-Hasselbalch equation:
pH = pKa + log([A-]/[HA])
In this case, the pKa for H2CO3 is pKa = 6.35 (at 25°C). Rearranging the equation, we get:
[A-]/[HA] = 10^(pH - pKa) = 10^(9 - 6.35) ≈ 234.28
Therefore, the ratio between HCO3- and H2CO3 in the buffered solution is approximately 234.28:1.
To identify the principle conjugate acid/base pair and calculate their ratio in a buffered solution at pH 9.00, we first need to understand the concept of buffering.
A buffer is a solution that resists changes in pH when small amounts of acid or base are added to it. Buffers consist of a weak acid and its conjugate base or a weak base and its conjugate acid.
Let's go through each compound and identify the principle conjugate acid/base pair:
a. H2S: The weak acid H2S can act as a buffer in an acidic solution. Its conjugate base is HS-. Therefore, the principle conjugate acid/base pair is H2S/HS-.
b. Ethylenediamine dihydrochloride: Ethylenediamine dihydrochloride is a salt, not a weak acid or base. Therefore, it does not have a principle conjugate acid/base pair.
c. H3AsO4: The weak acid H3AsO4 can act as a buffer in an acidic solution. Its conjugate base is H2AsO4-. Therefore, the principle conjugate acid/base pair is H3AsO4/H2AsO4-.
d. H2CO3: The weak acid H2CO3 can act as a buffer in an acidic solution. Its conjugate base is HCO3-. Therefore, the principle conjugate acid/base pair is H2CO3/HCO3-.
Now, let's calculate the ratio between the principle conjugate acid and base in a solution buffered to pH 9.00. The pH of a buffer solution is determined by the ratio of the concentration of the conjugate acid to the concentration of the conjugate base. We can use the Henderson-Hasselbalch equation:
pH = pKa + log ([A-]/[HA])
Where:
pH = 9.00 (given)
pKa = -log(Ka) (dissociation constant of the acid)
[A-] = concentration of the conjugate base
[HA] = concentration of the conjugate acid
Rearrange the equation to solve for the ratio [A-]/[HA]:
[A-]/[HA] = 10^(pH - pKa)
Since we do not have the specific values of the pKa for each compound, we cannot calculate the exact ratio between the conjugate acid and base for H2S, H3AsO4, and H2CO3. To calculate the ratio accurately, we need the pKa values specific to each acid.
However, based on the pH values provided, we can assume that the ratio of the conjugate base to acid will be higher in solutions buffered to a pH of 9.00, indicating a more basic condition.