perform the calculation required for100ml of 0.2 M sodium acetate buffer of pH 5.0. If you are given a bottle of sodium acetate acetate(mw =82 and a bottle of concentrated HCl of normality =11.7). After the calculation, prepare the buffer , check the pH of your calculation and comment on your result . Prepare 1:1, 1:4, 1:10, and 1:100 diluting your buffer and obtained pH reading for them
I can get you started.
For pH = 5.00 start with the HH equation and solve for base/acid ratio.
5.00 = 4.74 + log(b/a)
b/a = about 1.82 or
base = 1.82*acid (equation 1)
base + acid = 20 millimoles.
Solve those two equations simultaneously. I get something like 13 for base and 7 for acid but those are approximate. You need to go through and obtain better numbers.
You want 100 mL 0.2M buffer which is 20 millimols. I would start with 0.2 x 82 = about 16.4 g sodium acetate and this i to be divided up as 20
.......Ac^- + H^+ ==> HAc
I......20.......0.......0
add............x.........
C.....-x......-x.........x
E.....20-x....x.........7
You want x to be 7; therefore, 20-x = 13. Convert those to mL 11.7M HCl to be added and I'll leave the dilutions to you. You should go through a quick check to make sure what you're preparing actually is pH = 5.00
pH = 4.74 x log(13/7) = 5.00
Dr. Bob222, I’m posting this because I was working on it on a word document and had to go and take care of something before I was able to finish the dilution part; I didn't want to do this much work and not be able to post it. I am at least glad that we were on the same page on how to tackle this problem.
NaC2H3O2 + HCl --> HC2H3O2 + NaCl
You will need the following equation:
pH=pka+log([A-]/[HA])
Where
pH=5
pKa=4.76
Solving for [A-]/[HA]
10^(pH-pka)=[A-]/[HA]
Which should give you a ratio of 1.74
You need 0.2 M of the buffer, so you need (100mL)*0.2M = 0.02 moles of sodium acetate/acetic acid
0.02= A- + HA
And
1.74=[A-]/[HA]
Substituting one equation into the other, 1.74=0.02-HA/HA
Solving for HA, which is the amount of HCl needed, gives 0.00730 moles of HCl; this is so because HCl completely dissociates.
0.02 moles of sodium acetate*(82 g/1 mole)= mass of sodium acetate.
11.7N HCl=11.7M HCl
(0.00730 moles of HCl/11.7M)*10^3= volume of HCl in mL
100mL-volume of HCl in mL= additional volume of solvent needed.
For the dilutions just take part of the solution and dilute it with solvent i.e., 1 part solution and 4 parts solvent for the 1:4 dilution; repeat as indicated from the stock solution that you made.
To prepare a 100 mL sodium acetate buffer of pH 5.0 with a concentration of 0.2 M, we need to follow these steps:
Step 1: Calculate the amount of sodium acetate (NaC2H3O2) needed.
Using the formula: Moles = (Molarity * Volume) / 1000
Moles = (0.2 M * 100 mL) / 1000 = 0.02 moles
Since the molecular weight (MW) of sodium acetate is 82 g/mol,
Mass = Moles * MW = 0.02 moles * 82 g/mol = 1.64 g
Thus, you will need 1.64 grams of sodium acetate.
Step 2: Prepare the buffer.
Dissolve the calculated amount of sodium acetate (1.64 grams) in distilled water and make up the final volume to 100 mL. Stir well to ensure complete dissolution.
Step 3: Check the pH of the buffer.
Using a pH meter or pH indicator paper, measure the pH of the prepared buffer. The target pH is 5.0.
Comment on the result:
Compare the measured pH to the desired pH of 5.0. If the measured pH is close to 5.0, the preparation was successful. However, if there is a significant difference, adjustments can be made by adding small amounts of either sodium acetate or hydrochloric acid (HCl) to bring the pH closer to 5.0.
Step 4: Dilute the buffer.
To prepare dilutions of the buffer, you can take aliquots of the prepared buffer (100 mL) and dilute them as follows:
1:1 Dilution: Take 50 mL of the buffer and add 50 mL of distilled water.
1:4 Dilution: Take 20 mL of the buffer and add 80 mL of distilled water.
1:10 Dilution: Take 10 mL of the buffer and add 90 mL of distilled water.
1:100 Dilution: Take 1 mL of the buffer and add 99 mL of distilled water.
Step 5: Measure the pH of each dilution.
Using a pH meter or pH indicator paper, measure the pH of each of the dilutions prepared in Step 4. Compare the pH values obtained with the original buffer pH (5.0).
To prepare a 100ml of 0.2 M sodium acetate buffer with a pH of 5.0 using sodium acetate and concentrated HCl, you will need to follow these steps:
Step 1: Calculate the moles of sodium acetate required.
Molarity (M) = moles of solute / volume of solution (in liters)
Rearranging the equation to solve for moles:
moles of solute = Molarity × volume of solution (in liters)
moles of sodium acetate = 0.2 M × 0.1 L (since you want to prepare 100ml = 0.1 L)
moles of sodium acetate = 0.02 moles
Step 2: Convert moles of sodium acetate to grams.
To convert moles to grams, use the molecular weight (MW) of sodium acetate.
grams of sodium acetate = moles of sodium acetate × MW
grams of sodium acetate = 0.02 moles × 82 g/mol
grams of sodium acetate = 1.64 grams
Step 3: Prepare the buffer solution.
Weigh out 1.64 grams of sodium acetate and dissolve it in distilled water to make a total volume of 100ml.
Step 4: Check the pH of your buffer solution.
Use a pH meter or pH paper/strips to measure the pH of the buffer solution. In this case, you are aiming for a pH of 5.0.
Step 5: Comment on your result.
Compare the measured pH to the desired pH of 5.0. If the measured pH is close to 5.0, then your buffer preparation was successful. If it deviates significantly, it may be necessary to adjust the pH by adding small amounts of either HCl or sodium hydroxide (NaOH), while continually checking the pH until the desired pH is achieved.
Step 6: Prepare the desired dilutions.
Prepare the dilutions by taking a specified volume (e.g., 1:1 means taking an equal volume) of the original buffer solution and diluting it with distilled water to achieve the desired final volume. For example, to prepare a 1:1 dilution, take 50ml of the original buffer and dilute it with 50ml of distilled water.
Step 7: Measure the pH of each dilution.
Using a pH meter or pH paper/strips, measure the pH of each dilution and record the results.
By performing these calculations and steps, you should be able to prepare the 0.2 M sodium acetate buffer, check the pH, and obtain pH readings for the different dilutions. Keep in mind that small variations in pH may occur due to experimental factors, but the trends should remain consistent.