Question

Suggest a range of sample masses for the indicated primary standard if it is desired to use between 35 and 45mL of titrant:
(a) 0.175 M HClO4 titrated against Na2CO3(CO2 product)
(b) 0.085 M HCl titrated against Na2C2O4
Na2C2O4-->Na2CO3+CO
CO3(2-)+2H(+)-->H2O+CO2
(c) 0.150 M NaOH titrated against benzoic acid
(d) 0.050 M Ba(OH)2 titrated against KH(IO3)2
(e) 0.075 M HClO4 titrated against TRIS
(f) 0.050 M H2SO4 titrated against Na2B4O7 * 10 H20
reaction:
B4O7(2-)+2 H30(+)+3H20-->4H3BO3

Answer 1

a.
2HClO4 + Na2CO3 ==> 2NaCl + 2H2O

mols HClO4 = M x L = 0.035 x 0.175 = approx 0.006125
mols Na2CO3 = 1/2 that from 2 mol HClO4 = 1 mol Na2CO3
mol Na2CO3 = grams/molar mass or grams = mols x molar mass = 0.00306 x 106 = approx 0.320 g.
Now do the same thing with 45 mL instead of 35 mL to get the range. In practice you take approx the average.