What volume (in milliliters) of 0.180 M NaOH should be added to a 0.135 L solution of 0.0230 M glycine hydrochloride (pKa1 = 2.350, pKa2 = 9.778) to adjust the pH to 2.73?
Plz help, I'm not sure how to answer the question!
Thank you!!
Well, if you're not sure how to answer the question, maybe I can add some clowny humor to lighten the mood! Why don't we bring in a musical octopus to help with the calculations? I hear they have a great sense of rhythm and an affinity for math! Just kidding, enough clowning around. Let's get serious now.
To solve this problem, we need to use the Henderson-Hasselbalch equation, which relates the pH of a solution to the pKa and ratio of the concentrations of the acid and its conjugate base. In this case, glycine hydrochloride (GlyHCl) is the acid and its conjugate base is glycine (Gly).
The Henderson-Hasselbalch equation is:
pH = pKa + log([A-]/[HA])
Given that the pKa of GlyHCl is 2.350, the pH is 2.73, and the concentration of GlyHCl is 0.0230 M, we can rearrange the equation to solve for the concentration of glycine ([A-]):
2.73 = 2.350 + log([A-]/0.0230)
Now, we need to solve for [A-]. Taking the antilog (10^x) of both sides of the equation, we get:
10^(2.73 - 2.350) = [A-]/0.0230
Simplifying further:
10^0.38 = [A-]/0.0230
3.792 = [A-]/0.0230
Multiplying both sides by 0.0230:
3.792 * 0.0230 = [A-]
0.0874 = [A-]
Now that we know the concentration of glycine ([A-]) is 0.0874 M, we can determine the volume (in milliliters) of 0.180 M NaOH needed to adjust the pH. To do that, we need to calculate the moles of glycine (Gly) using the equation:
moles = concentration * volume
0.0874 = 0.135 * volume
Solving for the volume:
volume = 0.0874 / 0.135
volume ≈ 0.648 mL
So, approximately 0.648 milliliters of 0.180 M NaOH should be added to the solution to adjust the pH to 2.73.
Hope that helps, and remember, a little laughter can always lighten the chemistry mood!
To calculate the volume of NaOH needed to adjust the pH of the solution, we need to determine the moles of glycine hydrochloride and NaOH required for the reaction.
Step 1: Determine the moles of glycine hydrochloride:
Moles of glycine hydrochloride = concentration * volume
Moles of glycine hydrochloride = 0.0230 M * 0.135 L
Step 2: Calculate the moles of NaOH required for the reaction:
Since glycine hydrochloride is a diprotic species with pKa1 = 2.350 and pKa2 = 9.778, we need to find the species present at pH 2.73.
At pH 2.73, glycine hydrochloride is mostly protonated (1+).
Therefore, we only need to consider the first pKa value for the reaction:
H2A+ (glycine hydrochloride) + OH- (NaOH) → HA (glycine) + H2O
The balanced equation shows that 1 mole of glycine hydrochloride reacts with 1 mole of NaOH.
Hence, the moles of NaOH required = moles of glycine hydrochloride.
Step 3: Convert the moles of NaOH to volume (in milliliters):
Volume of NaOH (mL) = moles of NaOH / concentration of NaOH
Remember to convert the volume to milliliters if necessary.
Let's calculate the volume of NaOH:
Step 1:
Moles of glycine hydrochloride = 0.0230 M * 0.135 L = 0.00310 moles
Step 2:
Moles of NaOH required = 0.00310 moles
Step 3:
Volume of NaOH = 0.00310 moles / 0.180 M = 0.0172 L = 17.2 mL
Therefore, you would need to add 17.2 mL of 0.180 M NaOH to the solution of glycine hydrochloride to adjust the pH to 2.73.
To answer this question, we need to consider the stoichiometry of the chemical reaction between NaOH and glycine hydrochloride, as well as the dissociation of glycine hydrochloride in water.
1. Begin by writing the balanced chemical equation for the reaction between NaOH and glycine hydrochloride:
NaOH + H2NCH2COOH.HCl -> H2O + NaCl + H2NCH2COOH
2. Determine the number of moles of glycine hydrochloride in the solution:
Moles of glycine hydrochloride = concentration x volume
Moles of glycine hydrochloride = 0.0230 M x 0.135 L
3. Since glycine hydrochloride is a diprotic acid, it will dissociate twice. We need to determine the concentration of the dissociated forms of glycine hydrochloride.
Let x be the concentration of H2NCH2COOH and H+ (since they dissociate together), and y be the concentration of H2NCH2COO-.
Using the given pKa values, we can set up an equilibrium expression for the dissociation:
Ka1 = [H+][H2NCH2COO-] / [H2NCH2COOH]
Ka2 = [H+][H2NCH2COOH] / [H2NCH2COO-]
Since we are given the pH value and the pKa values, we can use the Henderson-Hasselbalch equation to relate the concentrations of the conjugate acid and base forms:
pH = pKa + log([H2NCH2COO-] / [H2NCH2COOH])
4. Using the Henderson-Hasselbalch equation, we can calculate the concentration of H2NCH2COOH and H2NCH2COO-:
pH = 2.73
pKa1 = 2.350
pKa2 = 9.778
Substitute these values into the Henderson-Hasselbalch equation and solve for [H2NCH2COO-]/[H2NCH2COOH].
5. With the concentration of the dissociated forms of glycine hydrochloride, we can calculate the concentration of NaOH needed to adjust the pH. Since the mole ratio between NaOH and H2NCH2COOH is 1:1, the concentration of NaOH will be the same as the concentration of H2NCH2COOH.
6. Finally, calculate the volume of 0.180 M NaOH needed to provide the required concentration:
Volume of NaOH = moles of NaOH / concentration of NaOH
By following these steps, you should be able to calculate the volume of 0.180 M NaOH needed to adjust the pH of the solution to 2.73.
the Henderson-Hasselbach equation:
2.73 = 2.35 - log( 0.0031/(0.18V))