Question

You dissolve 0.38 g of potassium chloride (KCl) in 625 ml of water.What is the molarity of the solution?(From the periodic table: 1 mol K = 39.10 g; 1 mol Cl = 35.453 g)Enter the value rounded to three decimal places with no unitsPlease help

Answer 1

Step 1

Molarity is defined as follows:

`Molarity\text{ \lparen M or mol/L\rparen = }\frac{moles\text{ of KCl}}{Volume\text{ in liters of the solution}}`

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Step 2

Information provided:

A solution made up of KCl + Water (H2O),

0.38 g KCl

625 mL H2O x (1 L/1000 mL) = 0.625 L

(Note: we need the volume of the solution in L, but we don't have the density of water or the density of solution so we assume the volume of water equal to the volume of water used)

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Information needed:

The molar mass of KCl = 39.10 g/mol + 35.453 g/mol = 74.553 g/mol

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Step 3

The number of moles of KCl, n

n = mass of KCL/the molar mass of KCl

n = 0.38 g/75.553 g/moles = 5.03x10^-3 moles

Molarity,

Molarity = 5.03x10^-3 moles/0.625 L = 8.048x10^-3 M

Answer: 8.048x10^-3