Solutions Part II DHS Chemistry Chapter 15

I. Concentrations of Solutions The concentration of a solution is a measure of the amount of solute that is dissolved in a given quantity of solvent. Amount of solute vs. amount of water

Dilute vs Concentrated photo by M.Ferrer Little solute a lot of solute

Very Concentrated Photo by Michael Solorio

Less Concentrated photo by Nicholas Dumlao

Concentrated solutions A concentrated solution is one that contains a high concentration of solute.

Dilute solutions A dilute solution contains a small concentration of solute.

Pictorial Representation

Pictorial Representation

There are several ways to express concentration There are several ways to express concentration. These include: percent solutions (by volume or mass), molarity, or molality.

A. Percent Solutions

Percent Solutions % solute = amount of solute _ 100 TOTAL amount of solvent solution 3 types: (%m/m) same units (%v/v) same units (%m/v) needs to be g/mL

How much vinegar is just acetic acid? 5% of vinegar is acetic acid

% by volume (% (v/v)) = volume of solute Percent by Volume % by volume (% (v/v)) = volume of solute 100 Volume of solution units must be the same (solute + solvent) Tip: watch out for the wording. You may need to add the volume of the solute and solvent to get the volume of the total solution

Percent by Mass % by mass (% (m/m)) = mass of solute 100 mass of solution *units must be the same (solute + solvent) Tip: watch out for the wording. You may need to add the mass of the solute and solvent to get the volume of the total solution

Percent Mass by Volume % mass by volume (% (m/v) = mass of solute (g) 100 volume of solution (mL) *units must g/mL

? % = 20 mL alcohol 30.8% 100 65 mL H2O %(v/v) = Volume of solute Ex 1: 20 mL of alcohol is diluted with water to a total volume of 65 mL. What is the percentage of alcohol, by volume? %(v/v) = Volume of solute 100 Volume of solution %(v/v)= ? % = 20 mL alcohol 30.8% Alcohol by volume 100 65 mL H2O

30.8% of this solution is alcohol. The rest is water. 65 mL alcohol + water 20 mL alcohol 30.8% of this solution is alcohol. The rest is water.

Is white gold really gold? White Gold, 18 Karat Au 75% - Pt or Pd 25% Solute = platinum or palladium Solvent = gold

5 grams of my ring isn’t pure gold. If I had an 18k white gold ring that weighed 20g, how much of the ring isn’t pure gold? White Gold, 18 Karat Au 75% - Pt or Pd 25% 25% = ?g 100 20g 5 grams of my ring isn’t pure gold.

Ex 2 : A solution containing 7 g of NaCl in 165 g of solution Ex 2 : A solution containing 7 g of NaCl in 165 g of solution. What is the percent of NaCl by mass? 158 g of solvent (water) 4.24% ? % NaCl (m/m)= 7 g NaCl 100 165 g solution Solution = Solute + solvent Solution = 7 g + 158 g

Children’s Dose vs Adult Dose Diphenhydramine hydrochloride (active ingredient in allergy medicine like Benadryl)

How do you feed a child medicine when one tablet is too strong?

Liquid dose for children has been diluted to 12 Liquid dose for children has been diluted to 12.5 mg for every 5 mL of medicine

What percent by mass of diphenhydramine hydrochloride is in the solution? Liquid dose for children has been diluted to 12.5mg for every 5mL of medicine .0125 g = .250% (m/v) 5 mL 100

EX 3: A saline solution containing 3. 5 g of NaCl in 62 EX 3: A saline solution containing 3.5 g of NaCl in 62.5 mL of solution. What is the percent of NaCl, by mass. 5.60% ? % = 3.5 g NaCl 100 62.5 mL solution

EX 3: A saline solution containing 3. 5 g of NaCl in 62 EX 3: A saline solution containing 3.5 g of NaCl in 62.5 mL of solution. What is the percent of NaCl, by mass. 5.60% ? % = 3.5 g NaCl 100 62.5 mL solution

%(v/v)= 22.3 % = ? mL ethanol 26.8 mL 100 120 mL solution Ex 4: What volume of ethanol is needed to produce 120 mL of a 22.3% (v/v) ethanol solution? %(v/v)= 22.3 % = ethanol by volume (v/v) ? mL ethanol 26.8 mL 100 120 mL solution

2.8 % = 0.750 g glucose 100 26.8 mL ? mL glucose solution Ex 5: What volume of a 2.8% (m/v) glucose solution would you need to deliver to a patient who needs 750 mg of glucose? 2.8 % = glucose by volume (m/v) 0.750 g glucose 100 26.8 mL ? mL glucose solution

Practice If 10 mL of pure acetone is diluted with water to a total solution volume of 200 mL, what is the percent by volume of acetone in the solution? 2. A bottle of hydrogen peroxide is labeled 3.0% (v/v). How many mL of H2O2 are in a 400.0 mL bottle of this solution? 3. Calculate the grams of solute required to make 250 g of 0.10% MgSO4 (m/m). 4. A solution contains 2.7 g CuSO4 in 75 mL of solution. What is the percent (m/v) of the solution?

%(v/v)= ? % = 5.00 % 10 mL acetone 100 200 mL solution If 10 mL of pure acetone is diluted with water to a total solution volume of 200 mL, what is the percent by volume of acetone in the solution? %(v/v)= ? % = 5.00 % 10 mL acetone acetone by volume (v/v) 100 200 mL solution

%(v/v)= 3.00 % = ? mL H2O2 12.0 mL 100 400. mL solution 2. A bottle of hydrogen peroxide is labeled 3.0% (v/v). How many mL of H2O2 are in a 400.0 mL bottle of this solution? %(v/v)= 3.00 % = ? mL H2O2 12.0 mL H2O2 by volume (v/v) 100 400. mL solution

3. Calculate the grams of solute required to make 250 g of 0 3. Calculate the grams of solute required to make 250 g of 0.10% MgSO4 (m/m). %(m/m)= 0.10 % = ? g MgSO4 0.250 g MgSO4 by volume (v/v) 100 250 g solution

4. A solution contains 2. 7 g CuSO4 in 75 mL of solution 4. A solution contains 2.7 g CuSO4 in 75 mL of solution. What is the percent (m/v) of the solution? %(m/v)= 3.60 % ? % = 2.7 g CuSO4 CuSO4 by volume (m/v) 100 75 mL solution

Practice If 10 mL of pure acetone is diluted with water to a total solution volume of 200 mL, what is the percent by volume of acetone in the solution? 2. A bottle of hydrogen peroxide is labeled 3.0% (v/v). How many mL of H2O2 are in a 400.0 mL bottle of this solution? 3. Calculate the grams of solute required to make 250 g of 0.10% MgSO4 (m/m). 4. A solution contains 2.7 g CuSO4 in 75 mL of solution. What is the percent (m/v) of the solution? 5.00% acetone (v/v) 12.0mL H2O2 0.250g MgSO4 3.60% (m/v)

B. Molarity

Molarity Molarity (M) is the number of moles of a solute dissolved per liter of solution.

Molarity Molarity is also known as molar concentration and is read as “ __#__ molar” (Ex. a 2M HCl solution is read as two molar HCl” Note that the volume involved is the total volume of solution, not just the solvent.

Molarity Molarity (M) = moles of solute M = mol Liters of solution 1 L *if given grams, convert if to moles using the molar mass of the substance

Why are grams important? Moles Grams Molar mass ___g = 1 mole You can not directly measure moles, you must calculate the mass in grams first

How to Prepare a Solution To make 1.00 liter of a 1.00 molar (1.0 M) solution: 1) add 1.0 mol of solute to a volumetric flask 2) add about ¼ flask of distilled water. Swirl the flask till the solute is dissolved. 3) slowly add water until the final volume reads 1.00 L

Molarity EX 1. What is the molarity of a solution that contains 8 moles of CaCl2 in 50 mL of solution? M = mol 8 mol 160M CaCl2 1 L 0.05 L

Molarity EX 2. How many grams of NaCl are needed to make 500mL of a 0.2 M solution? .2 M M = ? mol .1 mol 1 L 0.5 L 0.1 mol NaCl 58.443 g NaCl =5.84 mol NaCl 1 mol NaCl

Using Molarity Ex 3: A saline solution contains 0.90 g NaCl in exactly 100 mL of solution. What is the molarity of the solution? Step 1: Calculate # moles 0.90g NaCl x 1 mol NaCl =0.0154 mol NaCl 58.443 g NaCl Step 2: mL  L 100 mL x 1 L = 0.100 L NaCl 1000 mL

0.154 M ? M M = 0.0154 mol 1 L 0.1 L Ex 3 continued Step 3: Calculate Molarity 0.154 M ? M M = 0.0154 mol 1 L 0.1 L

Ex 2: How many grams of solute are present in 562 mL of 0.24 M Na2SO4? M = mol  mol = M  L L mol = 0.24M Na2SO4 x .562L = 0.135mol

Convert from Moles to Grams 0.135mol Na2SO4 | 142g Na2SO4 = | 1 mol Na2SO4 = 19.2g Na2SO4

Practice A solution has a volume of 2.0 L and contains 36.0 g of glucose. If the molar mass of glucose is 180 g/mol, what is the molarity of the solution? 0.100M glucose 2. How many moles of ammonium nitrate are in 335 mL of 0.425 M NH4NO3? 0.142mol NH4NO3 3. How many grams of solute are in 250 mL of 2.0 M CaCl2 solution? 55.5gCaCl2 4. Describe how you would prepare 250 mL of a 0.2 M NaOH solution. Need 2.00g NaOH in 250mL of solution

Molar mass = 6(12.01g) + 12(1.008g) + 6(15.999g) = 1. A solution has a volume of 2.0 L and contains 36.0 g of glucose. If the molar mass of glucose is 180 g/mol, what is the molarity of the solution? Molarity = mol L Glucose = C6H12O6 Molar mass = 6(12.01g) + 12(1.008g) + 6(15.999g) = Calculate moles: 36.0g C6H12O6 | 1 mol C6H12O6 = mol C6H12O6 | XXX g C6H12O6 Calculate Molarity: XXXmol C6H12O6 = 0.100M glucose 2.0 L

C. Dilutions

C. Dilutions You can make a less concentrated solution by diluting it with solvent. The dilution reduces the grams of solute per unit volume, but the total amount of solute in solution does not change.

Diluted Solutions Before After Dilutions Dilutions

Moles of solute = Molarity x volume Moles of solute before dilution = Moles of solute after dilution Moles of solute = Molarity x volume Dilutions: M1V1 = M2V2

m1 v1 m2 v2 V1 = 20mL of stock solution (2M)(V1) = (0.400M)(100mL) Ex: How many mL of a stock solution of 2.00 M MgSO4 would you need to prepare 100.0 mL of 0.400 M MgSO4? Stock soln (2M)(V1) = (0.400M)(100mL) m1 v1 m2 v2 V1 = 20mL of stock solution

Ex. 2: Describe how to prepare 100 mL of 0.400M MgSO4 from 2M MgSO4. (see previous example) Add 20mL of 2M stock solution in a container and add solvent up to the 100mL mark

Practice 1. How many mL of a stock solution of 4.00 M KI would you need to prepare 250.0 mL of 0.760 M KI? 47.5mL of 4.00MKI 2. What volume must you dilute to make 50.0 mL of 0.20 M KNO3 from 4.0 M KNO3? 2.5mL of 4M KNO3 3. What is the molarity of a solution formed when you add 200 mL of water to 50 mL of 5.0 M HCl? 1.00M

V1 = 47.5mL of 4M stock solution 1. How many mL of a stock solution of 4.00 M KI would you need to prepare 250.0 mL of 0.760 M KI? (4M) (V1) = (0.760M) (250mL) m1 v1 m2 v2 V1 = 47.5mL of 4M stock solution

(4M) (V1) = (0.20M) (50mL) m1 v1 m2 v2 V1 = 2.5mL of 4M solution 2. What volume must you dilute to make 50.0 mL of 0.20 M KNO3 from 4.0 M KNO3? (4M) (V1) = (0.20M) (50mL) m1 v1 m2 v2 V1 = 2.5mL of 4M solution

(5.0M) (50mL) = (M2) (250mL) m1 v1 m2 v2 M2 = 1M of solution 3. What is the molarity of a solution formed when you add 200 mL of water to 50 mL of 5.0 M HCl? (5.0M) (50mL) = (M2) (250mL) m1 v1 m2 v2 M2 = 1M of solution

M2 = 0.0200 M is the concentration of the diluted solution EX. A chemist starts with 50 mL of a 0.40M NaCl solution and dilutes it to 1000 mL. What is the concentration of the dilute solution? Stock soln (0.4 M)(50 mL) = (?M)(1000 mL) M1 V1 M2 V2 M2 = 0.0200 M is the concentration of the diluted solution “of a” are key words to help link a Molarity and volume together

Practice What volume of a 3.00M KI stock solution would you use to make 0.300 L of a 1.25 M KI solution? 0.125 L How many milliliters of a 5.0M H2SO4 stock solution would you need to prepare 100.0 mL of a 0.25M H2SO4? 5.00 mL If you dilute 20.0 mL of a 3.0M solution to make 100.0 mL of solution, what is the molarity of the dilute solution? 0.600M

(3.00M) (V1) = (1.25M) (.300) (5M) (V1 mL) = (0.25M) (100 mL) Practice 1 (3.00M) (V1) = (1.25M) (.300) m1 v1 m2 v2 V1 = .125 L of 3M stock solution Practice 2 (5M) (V1 mL) = (0.25M) (100 mL) m1 v1 m2 v2 V1 = 5.00mL of 5M solution

M1 = 0.600M is the new concentration Practice 3 (3.0M) (20mL) = (M2) (100mL) m1 v1 m2 v2 M1 = 0.600M is the new concentration