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SOLUTIONS

AN INTRODUCTION

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Objectives• 1. What are different ways of expressing

the concentration of a solution? When is each used?

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Solutions• Solutions are homogeneous

mixtures of two or more substances– Homogeneous: thoroughly

mixed, even composition throughout

• Solute: substance being dissolved

• Solvent: substance doing the dissolving

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Quantities of Solutes in Solution

• A dilute solution is one that contains relatively little solute in a large quantity of solvent.

• A concentrated solution contains a relatively large amount of solute in a given quantity of solvent

• A saturated solution contains the maximum amount of solute that can be dissolved in a particular quantity of solvent at equilibrium at a given temperature.

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Solution Concentrations

• Need something more specific than concentrated and dilute

– Molarity

– Percent concentration

– Mass/Volume Percent

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Molarity

• Molarity is an expression of the concentration of a solution in moles of solute per liter of solution.

moles of soluteMolarity (M) =

liters of solution

A solute is a solution component that is dissolved in a solvent.

The solvent is the solution component) in which one or more solutes are dissolved to form the solution

Remember

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Molarity Example

Calculate the molarity of a solution made by dissolving 0.165 moles of sodium sulfate (Na2SO4) in enough water to form 0.500 L of solution

moles of soluteMolarity (M) =

liters of solution

2 42 4

0.165 mol of Na SOMolarity (M) = 0.330 M Na SO

0.500 L of solution

Read as ” 0.330 molar sodium sulfate”

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Molarity Example (2)

Calculate the molarity of a solution made by dissolving 6.00 moles of Hydrogen Chloride (HCl) in enough water to form 2.50 L of solution

moles of soluteMolarity (M) =

liters of solution

6.00 mol of HClMolarity (M) = 2.40 M HCl

2.50 L of solution

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Molarity Examples

Molarity of 0.00700 mol of Li2CO3 in 10.0 mL of solution

First convert to liters of solution1L

10.0mL 0.0100L1000mL

0.00700Molarity(M) 0.700

0.0100

molM

L

moles of soluteMolarity (M) =

liters of solution

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Molarity Examples11. Calculate the molarity of each of the following solutions.

a. 8.90 g of H2SO4 in 100.0 mL of solution

First we need to know how many moles of H2SO4 we have

Find Molar Mass of H2SO4

H 2 x 1.00794 g/mol = 2.016 g/mol

S 1 x 32.066 g/mol = 32.066 g/mol

O 4 x 15.9994 g/mol = 63.998 g/mol

Molar mass of H2SO4 = 98.080 g/mol

2 48.90 g H SO

100.0 mL2 4

2 4

1 mol H SO

98.080 g H SO 1000 mL

1 L

2 40.907M H SO

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Molarity Examplesb. 439 g of C6H12O6 in 1.25 L of solution

First we need to know how many moles of C6H12O6 we have

Find Molar Mass of C6H12O6

C 6 x 12.0107 g/mol = 72.0642 g/mol

H 12 x 1.00794 g/mol = 12.0953 g/mol

O 6 x 15.9994 g/mol = 95.9964 g/mol

Molar mass of C6H12O6 =180.1559 g/mol

Find moles of C6H12O6

6 12 66 12 6

1 mol C H O439 g 2.44mol C H O

180.1559 g

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Molarity Example (continued)

moles of soluteMolarity(M)

liters of solution

6 12 6

2.44Molarity(M) 1.95M C H O

1.25

mol

L

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Molarity ExamplesHow many grams of solute are needed to prepare each of the

following solutions? a. 2.00 L of 1.00 M NaOH First we need to know the mass of one mole of NaOH

Find Molar Mass of NaOH Na 1 x 22.989770 g/mol = 22.9898 g/molH 1 x 1.00794 g/mol = 1.0079 g/molO 1 x 15.9994 g/mol = 15.9994 g/molMolar mass of NaOH = 39.9971 g/mol

1.00 mol NaOH 39.9971 g 2.00L79.9942 80.0g NaOH

L 1 mol NaOH 1g

Board

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Molarity Examples

What volume of 6.00 M NaOH is required to contain 1.25 mol of NaOH?

1.25 mol NaOH 1 L0.208 L

6.00 mol NaOH

6.00 mol NaOH6.00 M NaOH

1 L

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Percent Concentrations

• Sometimes it is more convenient to express concentrations by percentages

• Percent by Volume

• Percent by mass

volume of solute% by volume = 100%

volume of solution

mass of solute% by mass = 100%

mass of solution

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Percent Composition Examples

What is the percent by volume of a solution made by dissolving 235 mL of ethanol in enough water to make exactly 500 mL of solution?

volume of solute% by volume = 100%

volume of solution

235 mL of Ethanol100% 47.0%

500 mL of Solution

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Volume Percentage ExampleDescribe how to make 775 mL of a 40.0% by volume solution of

acetic acid.

Solve for Volume of soluteVolume of solute = (% by volume) x (Volume of solution) 100%

Volume of solute = (40.0% soln) x (775 mL soln) 100%Volume of solute = 310 mL of acetic actic

Take 310 mL of acetic acid and add enough water to make 775 mL of solution

volume of solute% by volume = 100%

volume of solution

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Volumetric Glassware

• Glassware designed for precisely making specific concentrations of solutions

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Mass Percentage ExampleWhat is the percent by mass of a solution of 25.0 g of NaCl

dissolved in 475 g (475 mL) of water?.

First find total mass of solution

mass of solution = 25.0 g of NaCl + 475 g of water

= 500. g

mass of solute% by mass = 100%

mass of solution

25.0 g of NaCl% by mass = 100%

500 g of solution

= 5.00 % NaCl solution

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Mass Percentage ExampleDescribe how to prepare 275 g of an aqueous solution that is

5.50% glucose by mass.

Solve for mass of soluteMass of solute = (% by mass) x (Mass of solution)

100%

Mass of solute = (5.50%(mass) soln of glucose) x (275 g of soln)

100%

Mass of solute = 15.1 g of glucose

Mass of solvent needed = Mass of solution – Mass of solute

= 275 g – 15.1 g = 260 g of water

Take 15.1 g of glucose and dissolve in 260 g of water

mass of solute% by mass = 100%

mass of solution

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Mass/Volume PercentMass/volume percent is an expression of

concentration in which the mass of the solute is divided by the volume of the solution and that quotient multiplied by 100%.– Used in medicine

mass of solutemass/volume percent = 100%

Volume of solution

In medical applications mg/dL = milligrams/deciliter is commonly used

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Mass/Volume Percent

• For dilute aqueous solutions– Mass/Volume percent is close to Mass/Mass

percent– This is because the density of a dilute aqueous

solution is approximately 1 g/mL

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Extremely Dilute solutions

For extremely dilute solutionsConcentrations expressed as– Parts per million (ppm)– Parts per Billion (ppm)– Parts per trillion (ppt)

– 1 ppm is 1 mg/L

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Saturation Solubilities

• Curve gives maximum amount of solute dissolved at given temperature

• Most solubilities of ionic solids increase with Temperature