CHAPTER 7 SOLUTIONS

7.5 Molarity and Dilution

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MOLARITY (M)

Molarity (M)

• is a concentration term for solutions.

• gives the moles of solute in 1 L of solution.

• moles of soluteliter of solution

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PREPARING A 1.0 MOLAR SOLUTION

A 1.00 M NaCl solution is prepared

• by weighing out 58.5 g of NaCl (1.00 mole) and

• adding water to make 1.00 liter of solution.

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CALCULATION OF MOLARITY

What is the molarity of 0.500 L of NaOH solution if it

contains 6.00 g of NaOH?

STEP 1: Given 6.00 g of NaOH in 0.500 L of solution

Need molarity (mole/L)

STEP 2: Plan g NaOH mole NaOH molarity

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EXAMPLE

What is the molarity of 325 mL of a solution containing 46.8 g of NaHCO3?

1) 0.557 M

2) 1.44 M

3) 1.71 M

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EXAMPLE

What is the molarity of 225 mL of a KNO3 solution containing 34.8 g of KNO3?

1) 0.344 M2) 1.53 M3) 15.5 M

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MOLARITY CONVERSION FACTORS

The units of molarity are used as conversion factors in calculations with solutions.

Molarity Equality3.5 M HCl 1 L = 3.5 moles of HCl

Written as Conversion Factors3.5 moles HCl and 1 L

1 L 3.5 moles HCl

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CALCULATIONS USING MOLARITY

How many grams of KCl are needed to prepare 125 mL

of a 0.720 M KCl solution?

STEP 1: Given 125 mL (0.125 L) of 0.720 M KCl

Need g of KCl

STEP 2: Plan L KCl moles KCl g KCl

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EXAMPLE

How many grams of AlCl3 are needed to prepare

125 mL of a 0.150 M solution?

1) 20.0 g of AlCl3

2) 16.7 g of AlCl3

3) 2.50 g of AlCl3

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EXAMPLE

How many milliliters of 2.00 M HNO3 contain 24.0 g of

HNO3?

1) 12.0 mL2) 83.3 mL3) 190. mL

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DILUTION

In a dilution• water is added.• volume increases.• concentration decreases.

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COMPARING INITIAL AND DILUTED SOLUTIONS

In the initial and diluted solution,• the moles of solute are the same.• the concentrations and volumes are related

by the following equations:

For percent concentration:

C1V1 = C2V2

initial diluted

For molarity:

M1V1 = M2V2

initial diluted12

DILUTION CALCULATIONS WITH PERCENT

What volume of a 2.00% (m/v) HCl solution can be

prepared by diluting 25.0 mL of 14.0% (m/v) HCl solution?

Prepare a table:

C1= 14.0% (m/v) V1 = 25.0 mL

C2= 2.00% (m/v) V2 = ?

Solve dilution equation for unknown and enter values:

C1V1 = C2V2

V2 = 13

EXAMPLE

What is the percent (% m/v) of a solution prepared

by diluting 10.0 mL of 9.00% NaOH to 60.0 mL?

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DILUTION CALCULATIONS WITH MOLARITY

What is the molarity (M) of a solution prepared

by diluting 0.180 L of 0.600 M HNO3 to 0.540 L?

Prepare a table:

M1= 0.600 M V1 = 0.180 L

M2= ? V2 = 0.540 L

Solve dilution equation for unknown and enter values:

M1V1 = M2V2

M2 =

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EXAMPLE

What is the final volume (mL) of 15.0 mL of a 1.80 M

KOH diluted to give a 0.300 M solution?

1) 27.0 mL

2) 60.0 mL

3) 90.0 mL

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7.6 MOLARITY IN CHEMICAL REACTIONS

In a chemical reaction,• the volume and molarity of a solution are

used to determine the moles of a reactant or product.

molarity ( mole ) x volume (L) = moles 1 L

• if molarity (mole/L) and moles are given, the volume (L) can be determined.

moles x 1 L = volume (L) moles

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USING MOLARITY OF REACTANTS

How many mL of 3.00 M HCl are needed to completely

react with 4.85 g of CaCO3?

2 HCl(aq) + CaCO3(s) CaCl2(aq) + CO2(g) + H2O(l)

STEP 1: Given 3.00 M HCl; 4.85 g of CaCO3

Need volume in mL

STEP 2: Plan

g CaCO3 mole CaCO3 mole HCl mL HCl

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EXAMPLE

If 22.8 mL of 0.100 M MgCl2 is needed to completely

react 15.0 mL of AgNO3 solution, what is the molarity of

the AgNO3 solution?

MgCl2(aq) + 2AgNO3(aq) 2AgCl(s) + Mg(NO3)2(aq)

1) 0.0760 M2) 0.152 M3) 0.304 M

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EXAMPLE

How many liters of H2 gas at STP are produced

when Zn reacts with 125 mL of 6.00 M HCl?

Zn(s) + 2HCl(aq) ZnCl2 (aq) + H2(g)

1) 4.20 L of H2

2) 8.40 L of H2

3) 16.8 L of H2

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SOL7.7 PROPERTIES OF SOLUTIONSUTIONS

Solutions

• contain small particles (ions or molecules).

• are transparent.

• do not separate.

• cannot be filtered.

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C7.7 PROPERTIES OF SOLUTIONSOLLOIDS

Colloids

• have medium-size particles.

• cannot be filtered.

• can be separated by semipermeable

membranes.

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EXAMPLES OF COLLOIDS

Examples of colloids

include

• fog

• whipped cream

• milk

• cheese

• blood plasma

• pearls23

7.7 PROPERTIES OF SOLUTIONSSUSPENSIONS

Suspensions

• have very large particles.

• settle out.

• can be filtered.

• must be stirred to stay suspended.

Examples include: blood platelets, muddy water, and calamine lotion.

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SOLUTIONS, COLLOIDS, AND SUSPENSIONS

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Copyright © 2009 by Pearson Education, Inc.

EXAMPLENING CHECK

A mixture that has solute particles that do not settle out, but are too large to pass through a semipermeable membrane is called a

1) solution.2) colloid.3) suspension.

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OSMOSIS

In osmosis,• water (solvent) flows

from the lower solute concentration into the higher solute concentration.

• the level of the solution with the higher solute concentration rises.

• the concentrations of the two solutions become equal with time.

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OSMOSISSuppose a semipermeable membrane separates a 4%starch solution from a 10% starch solution. Starch is acolloid and cannot pass through the membrane, butwater can. What happens?

semipermeable membrane

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4% starch 10% starchH2O

WATER FLOW EQUALIZES• The 10% starch solution is diluted by the flow of

water out of the 4% and its volume increases.• The 4% solution loses water and its volume

decreases.• Eventually, the water flow between the two

becomes equal.

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7% starch

7% starch

H2O

OSMOTIC PRESSURE

Osmotic pressure is

• produced by the solute particles dissolved in a solution.

• equal to the pressure that would prevent the flow of additional water into the more concentrated solution.

• greater as the number of dissolved particles in the solution increases. 30

EXAMPLECHECK

A semipermeable membrane separates a 10% sucrose solution A from a 5% sucrose solution B. If sucrose is a colloid, fill in the blanks in the statements below.

1. Solution ____ has the greater osmotic pressure.

2. Water initially flows from ___ into ___.

3. The level of solution ____will be lower.

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OSMOTIC PRESSURE OF THE BLOOD

Red blood cells

• have cell walls that are semipermeable membranes.

• maintain an osmotic pressure that cannot change or damage occurs.

• must maintain an equal flow of water between the red blood cell and its surrounding environment.

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ISOTONIC SOLUTIONS

An isotonic solution• exerts the same osmotic

pressure as red blood cells.

• is known as a “physiological solution.”

• of 5.0% glucose or 0.90% NaCl is used medically because each has a solute concentration equal to the osmotic pressure equal to red blood cells. 33

H2O

HYPOTONIC SOLUTIONS

A hypotonic solution • has a lower osmotic

pressure than red blood cells.

• has a lower concentration than physiological solutions.

• causes water to flow into red blood cells.

• causes hemolysis: RBCs swell and may burst.

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H2O

HYPERTONIC SOLUTIONS

A hypertonic solution

• has a higher osmotic pressure than RBCs.

• has a higher concentration than physiological solutions.

• causes water to flow out of RBCs.

• cause crenation: RBCs shrink in size.

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H2O

DIALYSIS

In dialysis,• solvent and small solute particles pass through

an artificial membrane.

• large particles are retained inside.

• waste particles such as urea from blood are removed using hemodialysis (artificial kidney).

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EXAMPLES

Indicate if each of the following solutions is 1) isotonic, 2) hypotonic, or 3) hypertonic.

A.____ 2% NaCl solution B.____ 1% glucose solution C.____ 0.5% NaCl solution D.____ 5% glucose solution

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EXAMPLES

When placed in each of the following, indicate if a red

blood cell will1) not change, 2) hemolyze, or 3) crenate.

A.____ 5% glucose solution

B.____ 1% glucose solution

C.____ 0.5% NaCl solution

D.____ 2% NaCl solution

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EXAMPLES

Each of the following mixtures is placed in a dialyzing bag and immersed in pure water. Which substance, if any, will be found in the water outside the bag?

A. 10% KCl solution

B. 5% starch solution

C. 5% NaCl and 5% starch solutions

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