1. Calculate the amount of Na2HPO47H2O (in grams) needed to make 50 mL of a 0.40

Question

1. Calculate the amount of Na2HPO47H2O (in grams) needed to make 50 mL of a 0.40 M solution. (It isn't 5.36g)

2. Calculate the amounts of Na2HPO2 and NaH2PO4 (in grams) needed to prepare 200 mL of a buffer with pH = 8.25 so that the sum of concentrations of (HPO4)2- and (H2PO4)- ions is 0.5 M. pKa1=2.12, pKa2=7.21, pKa2=7.21, pKa3=12.38

3. Write the equations for the ionization of 3-aminophenol. Would this substance be more soluble in water at pH 2.0 or pH 8.0? Would you expect this substance to be absorbed into the bloodstream in the stomach or the intestines?

4. How does the intensity of the spot on the silica sheet relate to the solubility of the drug in the aqueous phase?

Can you try to show the work and explain? Thanks!

Explanation / Answer

Both answers above for #1 are wrong. Yes part of compound is disodium phosphate but you also have to include the 7H2O (Heptahydrate) in the mass calculation. Therefore it would be...

268.07g*0.05mL = 13.4035

13.4035*0.4M = 5.3614 g of disodium phosphate heptahydrate

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