Question

a buffer is prepared using 20g of Na2H2PO4 (MW=120g/mol) and 14.2g Na2HPO4 (MW=142g/mol) in 350mL of...

a buffer is prepared using 20g of Na2H2PO4 (MW=120g/mol) and 14.2g Na2HPO4 (MW=142g/mol) in 350mL of solution.?

what is pH of the solution?

For H3PO4, Ka1 = 7.5*10^-3 ; Ka2 = 6.2*10^-8 ; Ka3 = 4.2*10^-13

Science   Chemistry   
0 0
Add a commentTranscribed image text
Next >

Homework Answers

Answer #1

Ka2 = 6.2 x 10-8

pKa2 = -log(Ka2)

pKa2 = -log(6.2 x 10-8)

pKa2 = 7.21

mass NaH2PO4 = 20 g

moles NaH2PO4 = (mass NaH2PO4) / (molar mass NaH2PO4)

moles NaH2PO4 = (20 g) / (120 g/mol)

moles NaH2PO4 = 0.167 mol

mass Na2HPO4 = 14.2 g

moles Na2HPO4 = (mass Na2HPO4) / (molar mass Na2HPO4)

moles Na2HPO4 = (14.2 g) / (142 g/mol)

moles Na2HPO4 = 0.100 mol

According to Henderson-Hasselbalch equation,

pH = pKa + log([conjugate base] / [weak acid])

pH = pKa2 + log(moles Na2HPO4 / moles NaH2PO4)

pH = 7.21 + log(0.100 mol / 0.167 mol)

pH = 7.21 + log(0.6)

pH = 7.21 - 0.22

pH = 6.99

0 0
Know the answer?
Your Answer:

Post as a guest

Your Name:

What's your source?

Earn Coins

Coins can be redeemed for fabulous gifts.

Log In

Sign Up

Not the answer you're looking for?
Ask your own homework help question
Similar Questions
Phosphoric acid is a triprotic acid, and the Ka values are given below. Calculate pH, pOH,...
Phosphoric acid is a triprotic acid, and the Ka values are given below. Calculate pH, pOH, [H3PO4], [H2PO4 2-], [HPO4 -], and [PO4 3-] at equilibrium for a 5.00 M phosphoric acid solution. Ka1 = 7.5 x 10^-3 Ka2 = 6.2 x 10^-8 Ka3 = 4.2 x 10^-13
Given that the stepwise dissociation constants for phosphoric acid are: Ka1 = 7.5×10-3; Ka2 = 6.2×10-8;...
Given that the stepwise dissociation constants for phosphoric acid are: Ka1 = 7.5×10-3; Ka2 = 6.2×10-8; Ka3 = 4.8×10-13 To prepare 1.20 L of a buffer solution having an ionic strength of 0.150 and a pH of 7.50 would require: Answer to 3 sig figs. a) (mass) of Na2HPO4(anhydrous) and b) (mass) of NaH2PO4(anhydrous).
Calculate the pH and the equilibrium concentrations of H2PO4-, HPO42- and PO43- in a 0.0353 M...
Calculate the pH and the equilibrium concentrations of H2PO4-, HPO42- and PO43- in a 0.0353 M aqueous phosphoric acid solution. For H3PO4, Ka1 = 7.5×10-3, Ka2 = 6.2×10-8, and Ka3 = 3.6×10-13 pH = ? [H2PO4-] = ?M [HPO42-] = ?M [PO43-] = ?M
2The acid-dissociation constants of phosphoric acid (H3PO4) are Ka1 = 7.5 × 10-3, Ka2 = 6.2...
2The acid-dissociation constants of phosphoric acid (H3PO4) are Ka1 = 7.5 × 10-3, Ka2 = 6.2 × 10-8, and Ka3 = 4.2 × 10-13 at 25.0 °C. What is the molar concentration of phosphate ion in a 2.5 M aqueous solution of phosphoric acid? A) 0.13 B) 2.5 × 10-5 C) 8.2 × 10-9 D) 9.1 × 10-5 E) 2.0 × 10-19 Can you include the complete steps where Ka2 and Ka3 is used.
Calculate the pH of 0.103 M phosphoric acid (H3PO4, a triprotic acid). Ka1 = 7.5 x...
Calculate the pH of 0.103 M phosphoric acid (H3PO4, a triprotic acid). Ka1 = 7.5 x 10-3, Ka2 = 6.2 x 10-8, and Ka3 = 4.8 x 10-13. Hint, if you are doing much work, you are making the problem harder than it needs to be.
Another buffer found in blood is based on the equilibrium between dihydrogen phosphate and monohydrogen phosphate....
Another buffer found in blood is based on the equilibrium between dihydrogen phosphate and monohydrogen phosphate. The reaction is shown below: H2PO4^-(aq) + H2O(l)----> H3O^+(aq) + HPO4^-2(aq) If the pH of a blood sample was 7.10, what would you calculate as the ratio of (H2PO4^-) to (HPO4^-2)? (Ka1 = 7.5*10^-3, Ka2 = 6.2*10^-8, Ka3 = 3.6*10^-13)
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.
Arsenic acid, H3AsO4 (MW= 141.94 g/mol), is a triprotic acid. The Ka values for arsenic acid...
Arsenic acid, H3AsO4 (MW= 141.94 g/mol), is a triprotic acid. The Ka values for arsenic acid are Ka1 = 5.0 x 10^ -4, Ka2 = 8.0 x 10^ -8, and Ka3 = 6.0 x 10 ^ -10. What volumes of 0.25 M H3AsO4, 0.25 M NaOH, and distilled water are required to make a buffer with a pH = 8? The total [AsO4] = 0.05M and the total volume is 1 L.
Show how phosphoric, H3PO4, dissociates in water and calculate the pH of a 0.030 M solution...
Show how phosphoric, H3PO4, dissociates in water and calculate the pH of a 0.030 M solution of the acid. Ka1 = 7.5 x 10-3; K a2 = 6.2 x 10-8; Ka3 = 4.8 x 10-13
3. Show how phosphoric, H3PO4, dissociates in water and calculate the pH of a 0.030 M...
3. Show how phosphoric, H3PO4, dissociates in water and calculate the pH of a 0.030 M solution of the acid. Ka1 = 7.5 x 10-3; K a2 = 6.2 x 10-8; Ka3 = 4.8 x 10-13
ADVERTISEMENT
Need Online Homework Help?

Get Answers For Free
Most questions answered within 1 hours.

Ask a Question
ADVERTISEMENT