1. How many grams of Na2CO3 (FM 105.99) should be mixed with 4.64 g of NaHCO3 (F

Question

1. How many grams of Na2CO3 (FM 105.99) should be mixed with 4.64 g of NaHCO3 (FM 84.01) to produce 100. mL of buffer with pH 10.04? (Assume Kw = 1.011014 and Kaof NaHCO3 = 4.691011.)

2. How many milliliters of 0.201 M NaOH should be added to 25.0 mL of 0.0237 M salicylic acid (2-hydroxybenzoic acid) to adjust the pH to 3.51? (Assume Kw = 1.011014, andKa1 and Ka2 values for salicylic acid are 1.07103, and 2.291014, respectively.)

3. (a) Calculate the quotient [H3PO4]/[H2PO4] in 0.0547 M KH2PO4. (Assume Kw = 1.011014, Ka1 = 7.11103, Ka2 = 6.34108, and Ka3 = 4.221013.)

(b) Find the same quotient for 0.0547 M K2HPO4.

Explanation / Answer

1.

pH = pka + log(salt/acid)

pka = -logKa = -log(4.69*10^(-11)) = 10.32

No of mole of NaHcO3 = 4.64/84.007 = 0.05523 mol

10.04 = 10.32 +log(x/0.05523)

No of mol of Na2co3 = 0.029mol

mass of Na2CO3 = 0.029*106 = 3.074 grams

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