500 mL of a 0.4 M calcium nitrite contains ________ moles of calcium ions and ________ moles of nitrite ions.

Question

Quizplus · Accepted Answer

Calcium nitrite, Ca(NO2)2, dissociates into Ca2+ and NO2- ions in water. 
0.4 M concentration of calcium nitrite means there are 0.4 moles of calcium nitrite in 1 L of solution. 
So, in 500 mL (0.5 L) of solution, the moles of calcium nitrite = 0.4 x 0.5 = 0.2 moles. 
Since there is one mole of Ca2+ ion in one mole of calcium nitrite, there are also 0.2 moles of Ca2+ ions in 500 mL of 0.4 M calcium nitrite solution. 
Similarly, since there are two moles of NO2- ions in one mole of calcium nitrite, there are 0.4 x 2 = 0.8 moles of NO2- ions in 1 L of calcium nitrite solution. In 500 mL of solution, there are 0.4 moles of NO2- ions. 
Therefore, 500 mL of a 0.4 M calcium nitrite contains 0.2 moles of calcium ions and 0.4 moles of nitrite ions. So, the best choice is B.

500 ML of a 0