Molar Concentration and Solution Preparation Section 8 6

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Molar Concentration, and Solution Preparation Section 8. 6

Molar Concentration, and Solution Preparation Section 8. 6

Concentration • The concentration of a solution describes how much solute is dissolved in

Concentration • The concentration of a solution describes how much solute is dissolved in a unit of solution. Qualitative: “Dilute” vs. “Concentrated”

Quantitative: “What quantity of solute is dissolved, per unit of solution? ” • ratio

Quantitative: “What quantity of solute is dissolved, per unit of solution? ” • ratio of solute to solution General formula: quantity of solute concentration = quantity of solution

Expressing concentration Concentration can be calculated and expressed in a number of ways. For

Expressing concentration Concentration can be calculated and expressed in a number of ways. For example: A. Molar concentration (mol/L) B. Percentage concentration C. Parts (per million – ppm; per billion – ppb)

Molar concentration (mol/L) • • aka “amount concentration”, or “molarity” the most common way

Molar concentration (mol/L) • • aka “amount concentration”, or “molarity” the most common way to express concentration number of moles of solute per one litre of solution unit: moles per litre (mol/L) moles of solute (mol) concentration = volume of solution (L) n c= V concentration, in moles per litre amount of solute, in moles volume of solution, in litres

n c= V Example 1 A solution contains 4. 35 g of KOH (M=56.

n c= V Example 1 A solution contains 4. 35 g of KOH (M=56. 11 g/mol) dissolved in 3. 00 L of solution. Find the molar concentration.

Practice 1 n c= V What volume of 0. 25 mol/L solution can be

Practice 1 n c= V What volume of 0. 25 mol/L solution can be made using 14. 0 g of Na. OH (M=40. 00 g/mol)? Find the moles of Na. OH Use n and c to solve for V Ans: 1. 4 L

Practice 2 n c= V A 100. 0 -m. L bottle of skin lotion

Practice 2 n c= V A 100. 0 -m. L bottle of skin lotion contains zinc oxide, Zn. O (M=81. 39 g/mol). The concentration of zinc oxide in the skin lotion is 0. 915 mol/L. What mass of zinc is present in the bottle? 7. 45 g

Learning Checkpoint • The molar concentration of a solution describes the MOLES OF SOLUTE

Learning Checkpoint • The molar concentration of a solution describes the MOLES OF SOLUTE per LITRE OF SOLUTION. • It is calculated using the formula: n c= V

A standard solution is one whose precise concentration is known. Two methods of preparing

A standard solution is one whose precise concentration is known. Two methods of preparing a standard solution: A. by dissolving a measured amount of solid B. by diluting another, more concentrated, standard solution

Method A: By Dissolving a Solid Example 2: You want to make 1. 00

Method A: By Dissolving a Solid Example 2: You want to make 1. 00 L of a 0. 50 mol/L Na. Cl solution. Explain how you will do this. Calculate the required moles of solute. n = c x v = (0. 50 mol/L)(1. 00 L) n = 0. 50 mol Na. Cl Convert to a mass. m = n x M = (0. 50 mol)(58. 44 g/mol) m = 29 g Na. Cl (MNa. Cl = 58. 44 g/mol)

 Measure the required mass of solute, and add it to a beaker. Add

Measure the required mass of solute, and add it to a beaker. Add a small amount of H 2 O and mix. Transfer solution to a volumetric flask. Add enough H 2 O to bring the final (total) volume to 1. 00 L. • this is NOT the same as adding 1. 00 L of H 2 O! calibrated accurately to a fixed volume

Practice 3 Your supervisor needs you to make 500. 0 m. L of a

Practice 3 Your supervisor needs you to make 500. 0 m. L of a 0. 200 mol/L Na. OH solution. a) What mass of Na. OH is required? b) Describe how you will prepare this volume of solution.

Learning Checkpoint • To prepare a standard solution from a solid, dissolve the required

Learning Checkpoint • To prepare a standard solution from a solid, dissolve the required amount of solute in water, and then use a volumetric flask to obtain the desired TOTAL volume of solution.

Homework • Pg. 400 #1 -4 • Pg. 402 #1 -12

Homework • Pg. 400 #1 -4 • Pg. 402 #1 -12