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Solutions Part II DHS Chemistry Chapter 15

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**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

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**Dilute vs Concentrated**

photo by M.Ferrer Little solute a lot of solute

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Very Concentrated Photo by Michael Solorio

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Less Concentrated photo by Nicholas Dumlao

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**Concentrated solutions**

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

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

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**Pictorial Representation**

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**Pictorial Representation**

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**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.

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A. Percent Solutions

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**Percent Solutions % solute = amount of solute _**

TOTAL amount of solvent solution 3 types: (%m/m) same units (%v/v) same units (%m/v) needs to be g/mL

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**How much vinegar is just acetic acid?**

5% of vinegar is acetic acid

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**% by volume (% (v/v)) = volume of solute**

Percent by Volume % by volume (% (v/v)) = volume of solute 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

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Percent by Mass % by mass (% (m/m)) = mass of solute 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

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

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**? % = 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

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**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.

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**Is white gold really gold?**

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

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**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 g 5 grams of my ring isn’t pure gold.

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**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 g

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**Children’s Dose vs Adult Dose**

Diphenhydramine hydrochloride (active ingredient in allergy medicine like Benadryl)

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

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**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

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**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

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**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

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**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

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**%(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

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**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

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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 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?

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**%(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

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**%(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 mL bottle of this solution? %(v/v)= 3.00 % = ? mL H2O2 12.0 mL H2O2 by volume (v/v) 100 400. mL solution

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**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

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**4. A solution contains 2. 7 g CuSO4 in 75 mL of solution**

4. A solution contains 2.7 g CuSO4 in 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

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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 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)

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B. Molarity

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

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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.

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**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

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**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

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**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

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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

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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 g NaCl =5.84 mol NaCl 1 mol NaCl

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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 = mol NaCl g NaCl Step 2: mL L 100 mL x 1 L = L NaCl 1000 mL

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**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 = mol 1 L 0.1 L

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**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

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**Convert from Moles to Grams**

0.135mol Na2SO4 | 142g Na2SO4 = | 1 mol Na2SO4 = 19.2g Na2SO4

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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 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

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**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

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C. Dilutions

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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.

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Diluted Solutions Before After Dilutions Dilutions

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**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

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**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 mL of M MgSO4? Stock soln (2M)(V1) = (0.400M)(100mL) m1 v m v2 V1 = 20mL of stock solution

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**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

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Practice 1. How many mL of a stock solution of 4.00 M KI would you need to prepare mL of 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

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**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 mL of M KI? (4M) (V1) = (0.760M) (250mL) m1 v m v2 V1 = 47.5mL of 4M stock solution

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**(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 v m v2 V1 = 2.5mL of 4M solution

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**(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) m v m v2 M2 = 1M of solution

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**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) M V M V2 M2 = M is the concentration of the diluted solution “of a” are key words to help link a Molarity and volume together

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

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**(3.00M) (V1) = (1.25M) (.300) (5M) (V1 mL) = (0.25M) (100 mL)**

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

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**M1 = 0.600M is the new concentration**

Practice 3 (3.0M) (20mL) = (M2) (100mL) m v m v2 M1 = 0.600M is the new concentration

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