I need help finding how many grams of acid, KH2PO4, I need for my buffer by usin

Question

I need help finding how many grams of acid, KH2PO4, I need for my buffer by using Method #1 shown above.

Biochemists and other life scientists also need to control pH in their experiments and frequently prepare aqueous buffer solutions for enzyme assays, extraction solvents, incubation media, etc. Usually the biochemist knows the desired pH and the volume of buffer needed, but must make decisions about the buffer components and the buffer concentration. The buffer used depends in part on the desired pH. A weak acid with pKa-pH ± 1 is usually selected. The buffer concentration is the sum of the concentrations of the weak acid and its conjugate base and depends on how closely the pH must be controlled, the expected amount of acid or base to be released, and the desired ionic strength. A buffer may be prepared in a number of ways, three of which are given below: A butrer may be prépared in a number ol Ways, thrée ol Which afe given below, 1. Neutralization of a portion of the weak acid with sufficient strong base to give the desired ratio, [A TTHA]: HA + NaOH Na + A + H2O

Explanation / Answer

K2HPO4 + HCl -------> K2PO4- + Cl- + H2O

mol of K2HPO4 = mol of HCl = 1 M * 0.1 L = 0.1 mol ( Volume of buffer = 100 mL)

Now,

pH = pKa + log(Base / Acid)

6.90 = 6.85 + log( 0.1 / [KH2PO4])

KH2PO4 = 0.089 mol

Mass of KH2PO4 = 0.089 * 136.09 = 12.13 g

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