A solution of magnesium chloride that is 5.10% magnesium by mass has a density 1.17 g/mL. How many moles of Cl- ions are in 300. mL of the solution?

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`MgCl_2rarrMg^(2+)+2Cl^-`

Density of solution `= 1.17g/(ml)` .

Mass of 300ml of solution `= 1.17xx300=351g`

Since the % of Mg in `MgCl_2` is 5.1%

Mass of Mg in the solution `=351xx5.1/100=17.901g`

Molar mass of Mg `= 24.3g/(mol)`

Amount of Mg moles `=17.901/24.3 =0.737`

Amount of `Cl^-` ions `=2xx0.737 =1.474`

**So the amount of Chloride ions in 300ml of solution is 1.474mol.**

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