What is the concentration of K+ in 0.15 M of K2S? If CaCl2 is dissolved in water

Question

What is the concentration of K+ in 0.15 M of K2S?

If CaCl2 is dissolved in water, what can be said about the concentration of the Ca2+ ion?

It has the same concentration as the Cl ion.

Its concentration is half that of the Cl ion.

Its concentration is twice that of the Cl ion.

Its concentration is one-third that of the Cl ion.

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 575 mL of a solution that has a concentration of Na+ ions of 0.600 M ?

Explanation / Answer

1) The concentration of K+ in 0.15 M of K2S = 2 X 0.15 = 0.30

2) If CaCl2 is dissolved in water, what can be said about the concentration of the Ca2+ ion ?

A) Its concentration is half that of the Cl ion.

3) The concentration of Na+ ions of 0.600 M means concentration of Na3PO4 = 0.200M

0.2 = (mass of Na3PO4/ molar mass Na3PO4) X1000/575

mass of Na3PO4 = (0.2 X 164 X 575)/ 1000

                          = 18.86 g

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