Calculate the pH of a buffer solution prepared by mixing 75.0 mL of 1.25 M lactic acid and 40.0 mL of 0.75 M sodium lactate. (The pKa for lactic acid is 3.86. The molar mass for lactic acid is 90.1 g/mol and the molar mass for sodium lactate is 112.1 g/mol.)

pH = 3.37

Explanation:

A weak acid as lactic acid in a solution with sodium lactate (Its conjugate base) produce a buffer. The pH of this buffer is obtained using H-H equation:

pH = pKa + log [A-] / [HA]

Where pH is the pH of the buffer,

pKa is 3.86

And [] could be taken as the moles of A- = Sodium lactate and HA = Lactic acid.

Moles A-:

40.0mL = 0.0400L * (0.75mol / L) = 0.030 moles A-

Moles HA:

75.0mL = 0.0750L * (1.25mol / L) = 0.09375 moles HA

Replacing:

pH = 3.86+ log [0.030 moles A-] / [0.09375 moles HA]

number of molecules / avogadro's number * molecule molecular = mass

explanation:

we define a gram-molecular weight as the mass of one mole of any element or compound. a mole contains avogadro's number of units (molecules) –  

6.022

x

10

23

. so, dividing the number of molecules by avogadro's number gives us the number of moles. multiplying that by the molecular weight gives us the mass. from the periodic table we find the gram-molecular weight of u to be238 and of f to be19. so,  

u

f

6

will have a gram-molecular weight of 352g.