Ion concentration refers to the molar concentration of an ion in solution. It ma

Question

Ion concentration refers to the molar concentration of an ion in solution. It may be identical to, or greater or less than, the molar concentration of the compound containing the ion that was used to make the solution.

For soluble salts, the molarity of a particular ion is equal to the molarity of that compound times the subscript for that ion. For example, 1 M of AlCl3is 1 M in Al3+ and 3 M in Cl?. 1 M of (NH4)2SO4 is 2 M in NH4+ and 1 M in SO42?.

A scientist wants to make a solution of tribasic sodium phosphate, Na3PO4, for a laboratory experiment. How many grams of Na3PO4 will be needed to produce 525mL of a solution that has a concentration of Na+ ions of 0.700M ?

Explanation / Answer

Na3PO4 has 3 Na+ and 1 Po4^-3 ion

[Na+] = 3 * [Na3PO4]

[Na+] = 0.700M

[Na3Po4] =[Na+] / 3 = 0.700 / 3 = 0.233 M

So concentration of solution = 0.233 M

Volume = 525ml = 525 /1000 = 0.525L

Moles of Na3Po4 = concentration * volume in litres = 0.233 *0.525 = 0.122 moles

Grams of Na3Po4 = moles * molar mass Na3PO4=

0.122 * 163.94 =20.0 g (answer)

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