A simple problem that demonstrates the relations between mass, volume and density.

The density, in g/cm cubed, of Pt if 100.0 g occupies 4.67ml.

pH and Biochemistry

I need a little nudge to get me started: Determine the weight in grams of sodium dihydrogen phosphate (M.W.138.01) and disodium hydrogen phosphate (M.W 141.98) needed to preparte 1L if a standard buffer at pH 7.00 with a total phosphate concentration of 0.100M. Okay I know that the pKa is going to be 6.86. I am therefore going to take the difference of pH 7 and pH 6.86 to get 0.14. I then do 10^14 to get 1.38. But them I am lost after that. I can't seem to figure out the concentration. Once I have that I know that I can find the mass of each of the molecules. (Question also included in attachment)

Buffers

An unknown compound X, is thought to have a carboxyl group with a pka of 2.0 and another ionizable group with a pka between 5 and 8. When 75 ml of 0.1 M NaOH was added to 100 ml of a 0.1 m solution of X at pH 2.0, the pH increased to 6.72.Calculate the pka of the second ionizable group of X. I tried to solve this using the Henderson Hasselbalch equation. 6.72=pka2+log[A-]/[HA] 6.72=pka2+log[0.10/0.075] 6.72=pka2+log(1.33) 6.72=pka2+0.12 pka2= 6.60 But this does not seem to be the right answer. I think I don't have the proper proportions

need a chemist

I am looking for a chemist that can develop dye's, if you have exp doing dye's this project may be for you, please contact me so we can discuss further, contact me via email, with your number. Regards Michael Paulson jkremodel@aol.com

Calculate the pH

Calculate the pH upon diluting 2ml of 2 N HCL to a final volume of 100 ml? Calcuate the pH upon addition of 0.0075 mole of solid NaOH to 100 ml of a 0.1 M solution of acetic acid (pKa=4.7)? If equal molar amounts of Na2HPO4 and NaJpo4 are mixed in water, calcuate the resulting pH. The pKas of phosphoric acid are 2.1, 7.2, 12.4. Calculate the % dissociation of a 0.1M solution of weak acid(pKa=5.0)? Which of the following pairs would makw the best buffer at pH10.0? a. Acetic acid & sodium acetate b. NaH2PO4 & Na2HPO4 c. H2CO3 & NaHCO3 d. Methylammonium chloride & Methylamine