A buffer solution containing Na H_ 2 PO_4 and Na_ 2 H PO_ 4 is often kept in lab
ID: 958876 • Letter: A
Question
A buffer solution containing Na H_ 2 PO_4 and Na_ 2 H PO_ 4 is often kept in laboratories for use on burns caused from spilling either acid or base on Oneself. Write the reaction that occurs when Na H_ 2 PO_ 4 and Na_ 2 H PO_ 4 are dissolved in water. Explain what happens if first acid and then base is added to this buffer. What is the pH of a buffer prepared by dissolving 25.0 g of Na H CO_ 3 in 500 mL of an aqueous solution saturated with CO_ 2, where a saturated solution is 0.032 M in CO_ 2? CO_ 2(g) + H_ 2 O(l) right arrow H_ 2 CO_ 3(aq)Explanation / Answer
39. H2PO4- + H2O --------> HPO42- + H3O+
HPO42- + H2O -----------> PO43- + H3O+
Now if we add acid, we'll increase the concentration of the acid, increasing the formation of acid (in this case H3O+) and the equilibrium will shift to the product. On the other hand, if base is added, the concentration of the base in this case, the reactants, so it will increase the base concentrations and decrease the products, so equilibrium will shift to the reactants.
40. Calculate the moles of NaHCO3:
moles = 25 g / 84 g/mol = 0.2976 moles
[HCO3] = 0.2976 / 0.5 = 0.5952 M
pH = pKa + log(A-/HA)
pH = -log(4x10-7) + log(0.5952/0.032)
pH = 7.67
Hope this helps
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