Ch. 13 & 14 - Solutions II. Concentration

What is different between the glasses of Kool-aid?

Solution concentration can be described generally Dilute - reduced in strength, weak, watered down. Concentrated – stronger, pure. Has less water.

What is the problem with just using dilute and concentrated as descriptions of the solution concentration?

Is solution B dilute or concentrated? Solution A Solution B Solution C Is solution B dilute or concentrated? The terms dilute and concentrated are relative. Scientists need a more precise way of referring to the concentration of a solution.

Solution concentration can be described specifically Do you remember the “mole” from Stoichiometry? What is a mole? How might you use it to describe the concentration of a solution?

A. Concentration The amount of solute in a solution. Describing Concentration % by mass - medicated creams % by volume - rubbing alcohol ppm, ppb - water contaminants molarity - used by chemists molality - used by chemists

The ratio of the moles of solute to the volume of solution in liters. Molarity The ratio of the moles of solute to the volume of solution in liters. Moles of solute Molarity (M) = Volume in Liters of Solution

How to read Molarity 6.0 M NaCl Read: “6 molar solution of NaCl” Can be abbreviated 6M solution You must be careful to label the molarity with a capital M so that it is not confused with m for molality.

How to make a 6M NaCl solution using molarity (a) Add 6 moles NaCl to the volumetric flask. How would you measure that? 6 molesNaCl 58.443 g NaCl 1 mole NaCl = 351 g NaCl

How to make a 6M NaCl solution using molarity (b) Add distilled or deionized H2O to dissolve and mix the NaCl (c) Fill the flask with dH2O until you reach the 1000mL line.

Types of Calculations with Molarity: 1. Finding concentration of a solution. 2. Finding the mass of solute needed. 3. Finding the volume of solution made.

Finding Concentration Antifreeze is a solution of ethylene glycol, C2H6O2 in water. If 4.50 L of antifreeze contains 27.5 g of ethylene glycol, what is the concentration of the solution? 27.5 g C2H6O2 1 mol C2H6O2 62.08 g C2H6O2 4.5 L = 0.0984 mol/L or 0.0984 M C2H6O2

Finding Mass What mass of sodium carbonate, Na2CO3, is present in 50 ml of a 0.750M solution? Conversion Factor 50 ml 1 L 0.750 mol 105.99 g Na2CO3 1000 mL 1 L 1 mol Na2CO3 = 3.97 g Na2CO3

Finding Volume Conversion Factor What volume of 1.50 mol/L HCl solution contains 10.0 g of hydrogen chloride? 10.0 g HCl 1 mol HCl 1 L 36.46 g HCl 1.50 mol = 0.183 L or 183 mL

Practice Problems

Practice Problems 1. A 0.750 L aqueous solution contains 90.0 g of ethanol, C2H5OH. Calculate the molar concentration of the solution in mol/L.

Practice Problem 2. What mass of NaCl are dissolved in 152 mL of a solution if the concentration of the solution is 0.364 M?

Practice Problem 3. What mass of dextrose, C6H12O6 is dissolved in 325 mL of 0.258 M solution?

Practice Problem 4. A mass of 98 g of sulfuric acid, H2SO4, is dissolved in water to prepare a 0.500 M solution. What is the volume of the solution?

Practice Problem 5. A solution of sodium carbonate, Na2CO3, contains 53.0 g of solute in 215 mL of solution. What is its molarity?

Practice Problem 6. What is the molarity of a solution of HNO3 that contains 12.6 g of solute in 5.00 L of solution?

B. Molality mass of solvent only 1 kg water = 1 L water

B. Molality Find the molality of a solution containing 75 g of MgCl2 in 250 mL of water. 75 g MgCl2 1 mol MgCl2 95.21 g MgCl2 0.25 kg water = 3.2m MgCl2

B. Molality How many grams of NaCl are req’d to make a 1.54m solution using 0.500 kg of water? 0.500 kg water 1.54 mol NaCl 1 kg water 58.44 g NaCl 1 mol NaCl = 45.0 g NaCl

Practice Problem What is the molality of a solution made from 2.4 moles of NaCl and 0.80 kg of water?

Practice Problem What is the molality of a solution made from 63 g of HNO3 in 0.50 kg of water?

How much water is needed to make a 0.50 m solution from 3.2 g of NaCl? Practice Problem How much water is needed to make a 0.50 m solution from 3.2 g of NaCl?

Practice Problems What mass of CH3OH is needed to add to 1.20 kg of water to make a 3.00 m solution?

C. Dilution Preparation of a desired solution by adding water to a concentrate. Moles of solute remain the same.

C. Dilution What volume of 15.8M HNO3 is required to make 250 mL of a 6.0M solution? GIVEN: M1 = 15.8M V1 = ? M2 = 6.0M V2 = 250 mL WORK: M1 V1 = M2 V2 (15.8M) V1 = (6.0M)(250mL) V1 = 95 mL of 15.8M HNO3

Dilution Practice Water is added to 200. mL of a 2.0 M solution of CaCl2 to increase the volume of the solution to 400. mL. What is the new concentration?

Dilution Practice To what volume must 1.0 L of a 6.0 M solution of HCl be diluted in order to prepare a 0.2 M solution?

D. Preparing Solutions 1.54m NaCl in 0.500 kg of water 500 mL of 1.54M NaCl mass 45.0 g of NaCl add water until total volume is 500 mL mass 45.0 g of NaCl add 0.500 kg of water 500 mL water 45.0 g NaCl 500 mL mark volumetric flask

D. Preparing Solutions 250 mL of 6.0M HNO3 by dilution measure 95 mL of 15.8M HNO3 95 mL of 15.8M HNO3 combine with water until total volume is 250 mL 250 mL mark Safety: “Do as you oughtta, add the acid to the watta!” water for safety

Solution Preparation Lab Turn in one paper per team. Complete the following steps: A) Show the necessary calculations. B) Write out directions for preparing the solution. C) Prepare the solution. For each of the following solutions: 1) 100.0 mL of 0.50M NaCl 2) 0.25m NaCl in 100.0 mL of water 3) 100.0 mL of 3.0M HCl from 12.1M concentrate.