Question

Phosphoric acid is a triprotic acid with the following pKa values: pKa1=2.148, pKa2=7.198, pKa3=12.375 You wish...

Phosphoric acid is a triprotic acid with the following pKa values: pKa1=2.148, pKa2=7.198, pKa3=12.375 You wish to prepare 1.000 L of a 0.0100 M phosphate buffer at pH 7.720. To do this, you choose to mix the two salt forms involved in the second ionization, NaH2PO4 and Na2HPO4, in a 1.000 L volumetric flask and add water to the mark. What mass of each salt will you add to the mixture? mass NaH2PO4? mass Na2HPO4? What other combination of phosphoric acid and/or its salts could be mixed to prepare this buffer? (Check all that apply). H3PO4 and NaH2PO4 H3PO4 and Na2HPO4 H3PO4 and Na3PO4 NaH2PO4 and Na3PO4 Na2HPO4 and Na3PO4. Please help me!! Thank you so much :)

Homework Answers

Answer #1

pKa1 = 2.148 = [H+][H2PO4 -] / [H3PO4]
2.148 = x^2 / 0.01 - x
x^2 + 2.148x - 0.02148 = 0
x = [H2PO4-] = 0.00995M

pH = pKa + log[Na2HPO4]/[NaH2PO4]
7.55 = 7.198 + log[Na2HPO4]/[NaH2PO4]
0.352 = log[Na2HPO4]/[NaH2PO4]
2.25 = [Na2HPO4]/[NaH2PO4]
you will need 2.25 x the amount of Na2HPO4 as NaH2PO4
x / y = 2.25
x + y = 0.01

2.25y + y = 0.01
3.35y = 0.01
y = 0.003M = [NaH2PO4]
x = 0.007M = [Na2HPO4]

0.003moles NaH2PO4 x 120g/mole = 0.36g
0.007moles Na2HPO4 x 139g/mole = 0.973g

Know the answer?
Your Answer:

Post as a guest

Your Name:

What's your source?

Earn Coins

Coins can be redeemed for fabulous gifts.

Not the answer you're looking for?
Ask your own homework help question
Similar Questions
Phosphoric acid is a triprotic acid with the following pKa values: pka1=2.148 pka2=7.198 pka3=12.375 You wish...
Phosphoric acid is a triprotic acid with the following pKa values: pka1=2.148 pka2=7.198 pka3=12.375 You wish to prepare 1.000 L of a 0.0500 M phosphate buffer at pH 7.780. To do this, you choose to mix the two salt forms involved in the second ionization, NaH2PO4 and Na2HPO4, in a 1.000 L volumetric flask and add water to the mark. What mass of each salt will you add to the mixture?
Phosphoric acid is a triprotic acid with the following pKa values: pka1= 2.148 pka2= 7.198 pka3=...
Phosphoric acid is a triprotic acid with the following pKa values: pka1= 2.148 pka2= 7.198 pka3= 12.375 You wish to prepare 1.000 L of a 0.0300 M phosphate buffer at pH 7.680. To do this, you choose to mix the two salt forms involved in the second ionization, NaH2PO4 and Na2HPO4, in a 1.000 L volumetric flask and add water to the mark. What mass of each salt will you add to the mixture? What other combination of phosphoric acid...
Phosphoric acid (H3PO4) is a triprotic acid with the following pKa values: pKa1 = 2.15 pKa2...
Phosphoric acid (H3PO4) is a triprotic acid with the following pKa values: pKa1 = 2.15 pKa2 = 7.20 pKa3 = 12.35 a). You wish to prepare a 1.000 L of a 0.0450 M phosphate buffer at pH 6.8. Which of the following salts do you use (PICK 2) and what mass of each salt will you add to the mixture? H3PO4 (M.W.= 97.995) KH2PO4 (M.W.=136.086) Na2HPO4 (M.W.=141.959) AlPO4 (M.W.=121.953)
Phosphoric acid (H3PO4) is a triprotic acid with the following pKa values: pKa1 = 2.15 pKa2...
Phosphoric acid (H3PO4) is a triprotic acid with the following pKa values: pKa1 = 2.15 pKa2 = 7.20 pKa3 = 12.35 a). You wish to prepare a 1.000 L of a 0.0450 M phosphate buffer at pH 6.8. Which of the following salts do you use (PICK 2) and what mass of each salt will you add to the mixture? H3PO4 (M.W.= 97.995) KH2PO4 (M.W.=136.086) Na2HPO4 (M.W.=141.959) AlPO4 (M.W.=121.953) b). A concentrated phosphate buffer known as “phosphate buffered saline” (or...
1. Phosphoric acid (H3PO4) is a polyprotic acid with pKa1 = 2.2; pKa2 = 6.8; pKa3...
1. Phosphoric acid (H3PO4) is a polyprotic acid with pKa1 = 2.2; pKa2 = 6.8; pKa3 = 12.4. What is the pH (to the nearest 0.1 pH unit) of a buffer made from mixing 90 mL of 0.1 M phosphoric acid and 10 mL of 0.1 M NaH2PO4? 2. The pKa of acetic acid is 4.76. What volume of 2 M HCl can be added to 100 mL of 0.1M acetate buffer at pH 4.76 before it is 90% titrated...
Phosphoric acid, H3PO4(aq), is a triprotic acid, meaning that one molecule of the acid has three...
Phosphoric acid, H3PO4(aq), is a triprotic acid, meaning that one molecule of the acid has three acidic protons. Estimate the pH, and the concentrations of all species in a 0.350 M phosphoric acid solution. ​pKa1=2.16 pKa2=7.21 pKa3=12.32
Phosphoric acid, H3PO4(aq), is a triprotic acid, meaning that one molecule of the acid has three...
Phosphoric acid, H3PO4(aq), is a triprotic acid, meaning that one molecule of the acid has three acidic protons. Estimate the pH, and the concentrations of all species in a 0.350 M phosphoric acid solution. pKa1= 2.16 pKa2=7.21 pKa3=12.32 [H3PO4]= [H2PO4-]= [HPO4^2-]= [PO4^3-] [H+]= [OH-]= pH=
Phosphoric acid is a triprotic acid (Ka1 = 6.9× 10–3, Ka2 = 6.2× 10–8, and Ka3...
Phosphoric acid is a triprotic acid (Ka1 = 6.9× 10–3, Ka2 = 6.2× 10–8, and Ka3 = 4.8× 10–13). To find the pH of a buffer composed of H2PO4–(aq) and HPO42–(aq), which pKa value would you use in the Henderson-Hasselbalch equation? A) pKa1= 2.16 B) pKa2=7.21 C) pKa3= 12.32 Calculate the pH of a buffer solution obtained by dissolving 24.0 g of KH2PO4(s) and 43.0 g of Na2HPO4(s) in water and then diluting to 1.00 L.
Phosphoric acid, H3PO4(aq), is a triprotic acid, meaning that one molecule of the acid has three...
Phosphoric acid, H3PO4(aq), is a triprotic acid, meaning that one molecule of the acid has three acidic protons. Estimate the pH, and the concentrations of all species in a 0.400 M phosphoric acid solution. pKa1 pKa2 pKa3 2.16 7.21 12.32 H3PO4=______M H2PO4-=______M HPO42-=________M PO43-=________M H+=_______M OH-=_______M pH=
Phosphoric acid, H3PO4(aq), is a triprotic acid, meaning that one molecule of the acid has three...
Phosphoric acid, H3PO4(aq), is a triprotic acid, meaning that one molecule of the acid has three acidic protons. Estimate the pH, and the concentrations of all species in a 0.300 M phosphoric acid solution. pKa1=2.16 pKa2=7.21 pKa3=12.32 [H3PO4] M=? [H2PO4^-] M=? [HPO4^2-] M=? [PO4^3-] M=? [H+] M=? [OH^-] M=? pH=?