Multiple choice

20 ml of 0.2 M ${ Al}{ 2 }{ \left( { SO }{ 4 } \right) }{ 3 }$ is mixed with 20 ml of 6.6 M $Ba{ Cl }{ 2 }$, the concentration of ${ Cl}^{ - }$ in solution is:

  1. 0.2 M

  2. 6.6 M

  3. 0.02 M

  4. 0.06 M
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B Correct answer
Explanation

The concentration of chloride ions is determined by the dissociation of BaCl2. Each mole of BaCl2 provides 2 moles of Cl-. The molarity of Cl- is (2 * 6.6 M * 20 ml) / (20 ml + 20 ml) = 6.6 M.

AI explanation

The moles of Al2(SO4)3 are 0.02 L times 0.2 M, yielding 0.004 moles, providing 0.012 moles of sulfate ions. The moles of BaCl2 are 0.02 L times 6.6 M, yielding 0.132 moles, which provides 0.264 moles of chloride ions. When mixed, the 0.132 moles of Ba2+ precipitate with the available sulfate, but the chloride ions remain in the solution. Because the total volume doubles to 40 ml, the concentration of Cl- should be 0.264 moles divided by 0.04 L, which is 6.6 M. Note that while the final concentration of the chloride ion mathematically remains 6.6 M due to the overwhelming concentration of the BaCl2 solution, this implies the chloride concentration is unchanged rather than reflecting a newly calculated mixture value.

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