How would you prepare 1.000 L of a 0.200 M phosphate buffer at pH 6.90 using crystalline Na2HPO4 and a solution of 1.000 M HCl?
Use the Henderson-Hasselbalch equation. I don't know the value you are using for pk2 so I can't work the problem for you.
6.9 = pK2 + log base/acid
Solve for base/acid = ? That's equation 1.
Equation 2 is
base + acid = 0.2M
Solve those two equations simultaneously for base and acid concentrations
You want 1 L so convert M base and acid to mols.
...HPO4^2- + H^+ ==> H2PO4^- + H2O
I
C
E
Complete the ICE chart.
If you have any trouble repost but show your work and where you get stuck.
To prepare 1.000 L of a 0.200 M phosphate buffer at pH 6.90 using crystalline Na2HPO4 and a solution of 1.000 M HCl, follow these steps:
Step 1: Calculate the amount of crystalline Na2HPO4 needed.
- Determine the molecular weight of Na2HPO4. The atomic masses of Na, H, P, and O are approximately 23, 1, 31, and 16, respectively.
- Na2HPO4 has a molecular weight of 22.99 * 2 + 1.01 + 31.00 + 16.00 * 4 = 141.96 g/mol.
- Calculate the amount of Na2HPO4 needed:
- Molar mass = 141.96 g/mol
- Concentration (C1) = 0.200 M
- Volume (V1) = 1.000 L
- Amount (n) = C1 * V1 = 0.200 mol/L * 1.000 L = 0.200 mol
- Mass (m) = n * Molar mass = 0.200 mol * 141.96 g/mol = 28.39 g
Step 2: Prepare a solution with 28.39 g of crystalline Na2HPO4.
- Weigh out 28.39 g of crystalline Na2HPO4 using a balance.
- Add the weighed Na2HPO4 to a container, such as a beaker or flask.
Step 3: Add distilled water to the container.
- Add distilled water slowly to dissolve the Na2HPO4. Mix the solution thoroughly to ensure complete dissolution.
Step 4: Adjust the pH of the solution to 6.90 using 1.000 M HCl.
- Measure the pH of the solution using a pH meter or pH indicator strips.
- Add the 1.000 M HCl solution dropwise while continuously monitoring the pH.
- Stop adding HCl once the pH reaches 6.90. Note the volume of HCl added.
Step 5: Adjust the final volume to 1.000 L by adding more distilled water if necessary.
- If the final volume is less than 1.000 L after adding HCl, add distilled water to reach the desired volume.
- Mix the solution thoroughly to ensure homogeneity.
You have now prepared 1.000 L of a 0.200 M phosphate buffer at pH 6.90 using crystalline Na2HPO4 and a solution of 1.000 M HCl.
To prepare a 0.200 M phosphate buffer at pH 6.90 using crystalline Na2HPO4 and a solution of 1.000 M HCl, the following steps can be followed:
Step 1: Calculate the moles of Na2HPO4 needed.
- The molar concentration (Molarity) is defined as moles of solute per liter of solution.
- The desired final volume is 1.000 L, and the desired molar concentration is 0.200 M.
- So, the number of moles of Na2HPO4 needed can be calculated using the formula: moles = volume (L) x molar concentration.
- In this case, the moles of Na2HPO4 required would be 1.000 L x 0.200 M = 0.200 moles.
Step 2: Convert the moles of Na2HPO4 to grams.
- The molar mass of Na2HPO4 can be found using the atomic masses of each element in the compound.
- The molar mass of Na2HPO4 is: (2 x atomic mass of Na) + (atomic mass of P) + (4 x atomic mass of O)
= (2 x 22.99 g/mol) + 31.00 g/mol + (4 x 16.00 g/mol) = 142.00 g/mol.
- Multiply the moles of Na2HPO4 (0.200 moles) by its molar mass (142.00 g/mol) to obtain the grams needed: 0.200 moles x 142.00 g/mol = 28.4 grams of Na2HPO4.
Step 3: Prepare a solution of 0.200 M Na2HPO4.
- Dissolve 28.4 grams of crystalline Na2HPO4 in enough water to make a final volume of 1.000 L.
- Stir the solution until all the Na2HPO4 has dissolved completely.
Step 4: Calculate the volume of 1.000 M HCl needed.
- The Henderson-Hasselbalch equation can be used to determine the volume of 1.000 M HCl required to obtain the desired pH.
- The Henderson-Hasselbalch equation is given by the formula: pH = pKa + log([A-]/[HA]), where [A-] and [HA] are the concentrations of the conjugate base and acid, respectively.
- In this case, the pKa of the phosphate buffer system is 7.21.
- The desired pH is 6.90, so we can rearrange the Henderson-Hasselbalch equation to solve for [A-]/[HA]: [A-]/[HA] = 10^(pH - pKa).
[A-]/[HA] = 10^(6.90 - 7.21) = 0.106.
- Since we want a final volume of 1.000 L and the concentration ratio of [A-]/[HA] is 0.106, we can calculate the volume needed to achieve this concentration.
- Let the volume of 1.000 M HCl needed be V L, so 0.106 = V × (1.000 M)/(1.000V) ⇒ V = 0.106 L = 106 mL.
Step 5: Add 106 mL of 1.000 M HCl to the 1.000 L Na2HPO4 solution.
- Slowly add the 106 mL of 1.000 M HCl to the 1.000 L Na2HPO4 solution while stirring continuously.
- Make sure the final volume is still 1.000 L.
- The HCl will react with the Na2HPO4 to form the HPO4^2- ions required to establish the buffer system.
By following these steps, you would be able to prepare 1.000 L of a 0.200 M phosphate buffer at pH 6.90 using crystalline Na2HPO4 and a solution of 1.000 M HCl.