Question

During the phosphatase experiment you will use several different ph buffers. the ph value depends upon combing various ratios of 0.1m citric acid and 0.2m sodium phosphate dibasic (na2hpo4, m.w. = 142 g/mole). describe how you would make 300 ml of 0.2m sodium phosphate dibasic given a 500g bottle of na2hpo4. include the type and sizes of any measuring vessels that you use to make the solution.

Answer 1

First calculate mass of sodium hydrogen phosphate (Na₂HPO₄) needed for solution:
n(Na₂HPO₄) = V(Na₂HPO₄) · c(Na₂HPO₄)
n(Na₂HPO₄) = 0,3 dm³ · 0,2 mol/dm³
n(Na₂HPO₄) = 0,06 mol
m(Na₂HPO₄) = 0,06 mol · 142 g/mol
m(Na₂HPO₄) = 8,52 g.
Measure that mass on scale using spoon and beaker. Than dissolve salt in beaker with distilled water and pour that solution in volumetric flask (size 300 mL), pour distilled water to graduation mark.