University:
University of North Dakota
Course:
CHEM 121 | General Chemistry I
Academic year:

2023
Views:

80

Pages:

2
Author:

battabyssaceous

Concentration of solutions How can you describe the concentration of a solution? The federal government and state governments set standards limiting the amount of contaminants allowed in drinking water. How do you calculate the molarity of a solution? The concentration of a solution is a measure of the amount of solute that is dissolved in a given quantity of solvent. • • A solution that contains a relatively small amount of solute is a dilute solution. A concentrated solution contains a large amount of solute. In chemistry, the most important unit of concentration is molarity. • • Molarity (M) is the number of moles of solute dissolved in one liter of solution. Molarity is also known as molar concentration. The figure below illustrates the procedure for making a 0.5M, or 0.5-molar, solution. • • • Add 0.5 mol of solute to a 1-L volumetric flask half filled with distilled water. Swirl the flask carefully to dissolve the solute. Fill the flask with water exactly to the 1-L mark. To calculate the molarity of a solution, divide the number of moles of solute by the volume of the solution in liters. moles of solute Molarity (M) = liters of solution Calculating Molarity Intravenous (IV) saline solutions are often administered to patients in the hospital. One saline solution contains 0.90 g NaCl in exactly 100 mL of solution. What is the molarity of the solution? Analyze List the knowns and the unknown. Convert the concentration from g/100 mL to mol/L. The sequence is: g/100 mL → mol/100 mL → mol/L solution concentration = 0.90 g NaCl/100 mL molar mass NaCl = 58.5 g/mol solution concentration = ?M Calculate Solve for the unknown. Use the molar mass to convert g NaCl/100 mL to mol NaCl/100 mL. Then convert the volume units so that your answer is expressed in mol/L. The relationship 1 L = 1000 mL gives you the conversion factor 1000 mL/1 L. Evaluate Does the result make sense? • • The answer should be less than 1M because a concentration of 0.90 g/100 mL is the same as 9.0 g/1000 mL (9.0 g/1 L), and 9.0 g is less than 1 mol NaCl. The answer is correctly expressed to two significant figures.