## Info

Write the molar mass balance for the total molar concentration of the phosphate radical.

Solution: The solution to this problem is similar to the one discussed in the text, except that [spPO(Al] will be replaced by [spPO4Fein]. The second subscript, FeIII, stands for the ferric salt. The molar mass balance is

[ sppoFeiii ] = [ PO3-] + [ HPO4-] + [ H2PO-] + [ H3PO4 ] Ans

Example 8 State the symbol [spPO FeIII] in words.

Solution: [spPO4Fein] is the total molar concentration of the PO4 radical as a result of using a ferric salt. Ans

Example 9 The complexation reaction of the calcium ion with the carbonate

CaCO ^ Ca2+ + CO2— CaHCO+ ^ Ca2+ + HCO— CaOH+ ^ Ca2+ + OH— CaSO4 ^ Ca2++ SO4—

Write the molar mass balance for the total molar concentration of Ca.

Solution: Let [Car] represent the total molar concentration of Ca. Therefore,

[ Car ] = [ Ca2+] + [ CaCO3 ] + [ CaHCO+] + [ CaOH+] + [ CaSO4 ] Ans

Equivalent concentration and normality. This method of expressing concentrations is analogous to molar concentrations, with the solute expressed in terms of equivalents. One problem that is often encountered is the conversion of a molar concentration to equivalent concentration. Let [C] be the molar concentration of any substance, where the symbol [ ] is read as "the concentration of." Convert this to equivalent concentration.

To do the conversion, first convert the molar concentration to mass concentration by multiplying it by the molecular mass (MM). Thus, [C] (MM) is the corresponding mass concentration. By definition, the number of equivalents is equal to the mass divided by the equivalent mass (eq. mass). Therefore, the equivalent concentration,

The concentration expressed as geq/L is the normality. The symbol for normality is N.

Example 10 The concentration of Ca(HCO3)2 is 0.74 gmol/L. Convert this concentration to geq/L.

Solution:

MM = 40.1 (2) + 2{ 1 + 12 + 3 (16)} = 202.2 No. of reference species = 2

Therefore, eq. mass = 