Finding the Concentration of a Specific Ion in Solutino [ENDORSED]

[Mike Matthews 1D]

I'm comfortable finding the concentration of certain molecules in solution. However I'm confused because some of the problems on the homework ask for the concentration of specific ions in a solution. For example problem G21: "A solution is prepared by dissolving 0.500 g of KCl, 0.500 g of K2S, and 0.500 g of K3PO4 in 500 mL of water. What is the concentration in the final solution of (a) potassium ions; (b) sulfide ions?" If someone could explain how to do this problem it would help me a lot. Thank you

[Clara Hu 1G]

For finding the concentration of potassium ions, first find the amount in moles of KCl, K2S, and K3PO4 in the solution. Then, split each compound and calculate the total amount in moles of potassium ions, which is 0.0229 moles. Then find the concentration of the potassium ions by dividing the number of moles by the volume of water to get 0.0458mol/L. Then for the concentration of sulfur ions, do the same, and find the amount of sulfur ions (0.00454 moles) and divide by the volume of water to get 0.00907mol/L.

[Michelle Nguyen 2L]

Yup! After finding the number of moles of each compound, find the number of moles of K+ in each molecule using the subscripts (eg multiply the number of moles of K2S by 2 to get the number of moles of K+ in K2S). Add them all together and you get the total moles of K+ ion in solution. Divide by liters and you get molarity of K+ :D