prepare a phosphate buffer with pH= 7 from solid NaH2PO4 (pKa =7.21) and Na2HPO4.

1) calculate the ratio of [CB]/[acid]
I got the ratio as 0.62

2) calculate the mass of each component required to make 1L of a .1 M buffer solution

3) if the pH is 7.10, how would you adjust it to 7.0?

1. 0.62 is correct.

2. base/acid = 0.62 or
base = 0.62*acid (equation 1)
You want 0.1M x 1 L = 0.1 mol and
base + acid = 0.1 mol (equation 2)
Solve the two equation simultaneously (in which base and acid will be in mols), then convert mols to grams of each.

To prepare a phosphate buffer with pH = 7 from solid NaH2PO4 (pKa = 7.21) and Na2HPO4, follow these steps:

1) Calculate the ratio of [CB]/[acid]:
The Henderson-Hasselbalch equation is used to determine the ratio of [CB]/[acid]:
pH = pKa + log([CB]/[acid])

Given pH = 7 and pKa = 7.21, let's solve for [CB]/[acid]:
7 = 7.21 + log([CB]/[acid])
-0.21 = log([CB]/[acid])

Now, we can calculate the ratio using the antilog function:
[CB]/[acid] = 10^(-0.21)
[CB]/[acid] ≈ 0.62

2) Calculate the mass of each component required to make 1L of a 0.1 M buffer solution:
Molarity (M) is defined as moles per liter (mol/L).
Given that the desired molarity is 0.1 M, we can calculate the moles required:

Moles of CB (Na2HPO4):
Moles = Molarity x Volume (in L)
Moles of Na2HPO4 = 0.1 mol/L x 1 L = 0.1 mol

Moles of Acid (NaH2PO4):
Moles of CB (Na2HPO4) = Moles of Acid (NaH2PO4) × [CB]/[acid]
0.1 mol = Moles of Acid (NaH2PO4) × 0.62
Moles of Acid (NaH2PO4) = 0.1 mol / 0.62 ≈ 0.161 mol

Now, we can calculate the mass of each component:
Mass = Moles x Molar Mass

Mass of CB (Na2HPO4):
Mass of Na2HPO4 = Moles of CB (Na2HPO4) x Molar Mass of Na2HPO4
Molar Mass of Na2HPO4 = 22.99 g/mol (sodium) + 30.97 g/mol (phosphorus) + (4 x 16.00 g/mol) (oxygen)
Molar Mass of Na2HPO4 = 142.00 g/mol
Mass of Na2HPO4 = 0.1 mol x 142.00 g/mol ≈ 14.2 g

Mass of Acid (NaH2PO4):
Mass of NaH2PO4 = Moles of Acid (NaH2PO4) x Molar Mass of NaH2PO4
Molar Mass of NaH2PO4 = 22.99 g/mol (sodium) + 1.01 g/mol (hydrogen) + 30.97 g/mol (phosphorus) + (4 x 16.00 g/mol) (oxygen)
Molar Mass of NaH2PO4 = 119.98 g/mol
Mass of NaH2PO4 = 0.161 mol x 119.98 g/mol ≈ 19.34 g

Therefore, to make a 1L solution of a 0.1 M phosphate buffer with pH = 7, you will need approximately 14.2 g of Na2HPO4 and 19.34 g of NaH2PO4.

3) To adjust the pH from 7.10 to 7.00, you can use a weak acid or weak base to titrate the solution:

- If the pH needs to be lowered from 7.10 to 7.00, you can add a small amount of a strong acid, such as HCl, dropwise to the solution until the pH reaches the desired value. This will convert some of the phosphate ions to the acid form, lowering the pH.

- If the pH needs to be raised from 7.10 to 7.00, you can add a small amount of a weak base, such as NaOH, dropwise to the solution until the pH reaches the desired value. This will convert some of the phosphate ions to the conjugate base form, raising the pH.

It is important to add the titrating agent slowly and monitor the pH continuously to avoid over-adjustment.

To prepare a phosphate buffer with a pH of 7 using solid NaH2PO4 and Na2HPO4, you would follow these steps:

1) Calculate the ratio of [CB]/[acid]:
To calculate the ratio of [CB] (conjugate base) to [acid], use the Henderson-Hasselbalch equation:

pH = pKa + log([CB]/[acid])

Since the pH is equal to the pKa of 7.21, you can rearrange the equation to solve for [CB]/[acid]:

7 = 7.21 + log([CB]/[acid])
log([CB]/[acid]) = 7 - 7.21
log([CB]/[acid]) = -0.21

Now, you can calculate the ratio of [CB]/[acid] by taking the antilogarithm (usually base 10) of -0.21. You can do this using a scientific calculator or by using a logarithm table. The result is approximately 0.62.

(Note: The ratio does not need to be exact, as long as it is close enough for practical purposes.)

2) Calculate the mass of each component required to make 1L of a 0.1 M buffer solution:
In order to calculate the mass of each component, you need to know the molar mass of NaH2PO4 and Na2HPO4.

NaH2PO4 has a molar mass of:
Na (22.99) + H (1.01) + 2 * P (31.00) + 4 * O (16.00) = 119.98 g/mol

Na2HPO4 has a molar mass of:
2 * Na (22.99) + H (1.01) + P (31.00) + 4 * O (16.00) = 141.96 g/mol

Now you can calculate the mass of each component required to make 1L of a 0.1 M buffer solution:

For NaH2PO4:
Mass = molar mass * molarity * volume
Mass = 119.98 g/mol * 0.1 mol/L * 1 L = 11.998 g

For Na2HPO4:
Mass = molar mass * molarity * volume
Mass = 141.96 g/mol * 0.1 mol/L * 1 L = 14.196 g

Therefore, you would need approximately 12 g of NaH2PO4 and 14 g of Na2HPO4 to make 1L of a 0.1 M buffer solution.

3) If the pH is 7.10 and you want to adjust it to 7.0, you would need to add a small amount of a strong acid (such as HCl) to decrease the pH or a strong base (such as NaOH) to increase the pH. The specific amount would depend on the volume of the buffer solution and the strength of the acid or base being added.

To decrease the pH from 7.10 to 7.0, you could add a small amount of a strong acid dropwise while monitoring the pH until it reaches 7.0.

To increase the pH from 7.10 to 7.0, you could add a small amount of a strong base dropwise while monitoring the pH until it reaches 7.0.

It is important to note that adding too much acidic or basic solution can lead to significant changes in pH and may require starting the buffer preparation process again.