Which of the following solutions contains the smallest number of ions?
A) 539.8 mL of 1.0 M lithium nitrate
B) 305.6 mL of 2.0 M potassium hydroxide
C) 189.6 mL of 2.0 M iron(III) chloride
D) 246.8 mL of 1.0 M sodium sulfate
E) At least two of the above contain the smallest number of ions.

Question

Quizplus · Accepted Answer

To find the smallest number of ions, we need to multiply the molarity of each solution by the number of ions it breaks up into when dissolved in water.

A) LiNO3 dissociates into 3 ions: 1 Li+ ion and 2 NO3- ions
1.0 M LiNO3 = 1.0 mol LiNO3/L x 3 ions/mol = 3.0 M ions/L
539.8 mL = 0.5398 L x 3.0 M ions/L = 1.62 M ions

B) KOH dissociates into 2 ions: 1 K+ ion and 1 OH- ion
2.0 M KOH = 2.0 mol KOH/L x 2 ions/mol = 4.0 M ions/L
305.6 mL = 0.3056 L x 4.0 M ions/L = 1.22 M ions

C) FeCl3 dissociates into 4 ions: 1 Fe3+ ion and 3 Cl- ions
2.0 M FeCl3 = 2.0 mol FeCl3/L x 4 ions/mol = 8.0 M ions/L
189.6 mL = 0.1896 L x 8.0 M ions/L = 1.52 M ions

D) Na2SO4 dissociates into 3 ions: 2 Na+ ions and 1 SO42- ion
1.0 M Na2SO4 = 1.0 mol Na2SO4/L x 3 ions/mol = 3.0 M ions/L
246.8 mL = 0.2468 L x 3.0 M ions/L = 0.74 M ions

Therefore, choice D, 246.8 mL of 1.0 M sodium sulfate, has the smallest number of ions at 0.74 M ions/L.

Which of the Following Solutions Contains the Smallest Number of Ions