Question

I need help with a buffer equation. I am having a hard time answering the three questions on here.

The pH is 7.40 and the concentration in M is 0.100. the total volume in mL is 100.00. The pKa of H2PO4- is 7.21. The conjugate acid and base to make the phosphate buffer are H2PO4- and HPO4^2-

Equation (3) in the lab manual is pH = pKa + log (molesB / molesA).

Equation (1) is [buffer] = Stot / L

Thank you very much for the help

pH Upen with concentration (M) mL Buffer Assignment 100.00 Determine the Mass of Each Component py Thur Everyor Recall that buffers are formed from conjugate acid/base pairs. Using the information given about your assigned buffer, determine how much of each component (acid and base) you will need in order to prepare it in the lab. (This will require a system of equations because there are two "unknowns.") Ich gott Note: the conjugate acid in this case is H PO. , and the conjugate base is HPO.. 1. Using equation (3) in your lab manual, solve for the ratio of (moles B/moles A). sending work. E 2. From the ratio, solve for the moles B in terms of moles A. (Hint: you are not solving for the actual number of moles B at this point, you are only solving for the relationship of B to A.) ating tin me upd 3. Using your concentration and volume, solve equation (1) in the lab manual for Scot-

Answer 1

y Given piti pika a la (moles B (mole & pH = 7.40 pka = 7.21 Theis log finales B] - pH - pka -10-0.19 se conoles B) = 1 olg (ratio) 0.19 2) moles B moles = t A 1819 =) moles A = 10 moles B moles B = moles A 7819 3) Given [buffed] Stot/u. So Stot - [buffed x L sence ( Stot = 0.100 x 100.00 Stot = 10 [buffed] - 0.100 L = 100.00