Sagot :
Molarity (M)
Discussion:
Molarity is one of the commonly used units in chemistry. Molarity is defined as the number of moles of solute per liter of solution --- that is,
[tex]\boxed{\text{molarity} = \frac{\text{moles of solute}}{\text{volume of solution (L)}}}[/tex]
For example, a 1.46 [tex]M[/tex] glucose solution contains 1.46 mol of the solute (glucose) in 1 L of the solution. Of course, we do not always work with solution volumes of 1 L. Thus, a 500-mL solution containing 0.730 mol of glucose also has a concentration of 1.46 [tex]M.[/tex]
[tex]\\[/tex]
Problem:
What is the molarity of a solution made from 325.4 g of AlCl₃ with enough water to make 500.0 mL?
Given:
mass of solute = 325.4 g
volume of solution = 500.0 mL = 0.5000 L
solute: AlCl₃
Required:
molarity
Solution:
Step 1: Calculate the molar mass of solute.
molar mass of solute = (26.98 g/mol × 1) + (35.45 g/mol × 3)
molar mass of solute = 133.33 g/mol
Step 2: Calculate the number of moles of solute.
[tex]\text{moles of solute} = \frac{\text{mass of solute}}{\text{molar mass of solute}}[/tex]
[tex]\text{moles of solute} = \frac{\text{325.4 g}}{\text{133.33 g/mol}}[/tex]
moles of solute = 2.440561 mol
Step 3: Calculate the molarity of solution.
[tex]\text{molarity} = \frac{\text{moles of solute}}{\text{volume of solution (L)}}[/tex]
[tex]\text{molarity} = \frac{\text{2.440561 mol}}{\text{0.5000 L}}[/tex]
[tex]\boxed{\text{molarity} = 4.881 \: M}[/tex]
[tex]\\[/tex]
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