Chapter 15, Problem 19A

Interpretation Introduction

Interpretation:

Number of moles of each ion per litre in aCaCl₂ solution has to be calculated.

Concept Introduction:

Composition of a solution can be defined by expressing its concentration. The concentrations of solutions can be expressed in different ways, which are involved in the quantity of solute and the quantity of solution or solvent. Various methods are used to describe the concentration of the solution quantitatively. Some commonly used quantitative concentration terms are percent by mass, percent by volume, molarity, molality and mole fraction.

Molarity: Molarity is defined as the number of moles of solute present in one litre of the solution In expression, $\mathrm{Molarity}ofthesolution=\frac{Numberofmolesof the solute}{ Volume of the solution(inlitre)}$

Again $\mathrm{Number}ofmolesofsolute=\frac{Massofthesolute}{Molecularweightofthesolute}$

Answer to Problem 19A

0.221 moles of $C{a}^{2+}$ ions and 0.442 moles of $C{l}^{-}$ ions are present per litre in a CaCl₂ solution.

Explanation of Solution

  $\mathrm{Molarity}ofthesolution=\frac{Numberofmolesof the solute}{ Volume of the solution(inlitre)}$

Data given: Molarity of ${\mathrm{CaCl}}_2$ solution = 0.221 M.

  $\begin{array}{l}MolarityofCaC{l}_{2}solution=\frac{Numberofmolesof CaC{l}_2}{ Volume of CaC{l}_2 solution(inlitre)}\\ Numberofmolesof CaC{l}_2=MolarityofCaC{l}_{2}solution\times Volume of CaC{l}_2 solution(inlitre)\\ Numberofmolesof CaC{l}_2=0.221mol/litre\times 1litre=0.221mole\end{array}$

  ${\mathrm{CaCl}}_2\to C{a}^{2+}+2C{l}^{-}$

1 mole of ${\mathrm{CaCl}}_2$

gives 1 mole of ion and 2 moles ofions. So, 0.221 mole of 0.221 mole of ions and 0.442 moles of ions, 0.221 mole of ions and 0.442 mole of ions are present per litre in a CaCl₂ solution.