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Chapter 8 Solutions

8.1 Solutions

The water lost from the body is replaced by the intake of fluids.

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Solute and Solvent

Solutions• are homogeneous

mixtures of two or more substances

• contain a solute, usually in smaller quantity

• contain a solvent, usually in greater quantity

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Solutes• spread evenly

throughout the solution

• cannot be separated by filtration

• can be separated by evaporation

• are not visible but can give a color to the solution

Nature of Solutes in Solutions

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Examples of Solutions

The solutes and solvents in solutions can be

• solids• liquids• gases

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Identify the solute in each of the following solutions:

A. 2 g of sugar (1) and 100 mL of water (2)B. 60.0 mL of of ethyl alcohol(1) and 30.0 mL of methyl alcohol (2)

C. 55.0 mL of water (1) and 1.50 g of NaCl (2)

D. Air: 200 mL of O2 (1) and 800 mL of N2 (2)

Learning Check

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Identify the solute in each of the following solutions:

A. 2 g of sugar (1)

B. 30.0 mL of methyl alcohol (2)

C. 1.5 g of NaCl (2)

D. 200 mL of O2 (1)

Solution

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WaterWater• is the most common solvent• Review electronegativity -

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Water• is the most common solvent• Draw a water molecule• Electronegativity is a measure of the

tendency of an atom to attract a bonding pair of electrons. The Pauling scale is the most commonly used. Fluorine (the most electronegative element) is assigned a value of 4.0, and values range down to caesium and francium which are the least electronegative at 0.7.

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Water• is the most common solvent• is a polar molecule• forms hydrogen bonds between the hydrogen

atom in one molecule and the oxygen atom in a different water molecule

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Formation of a Solution

Na+ and Cl ions• on the surface of a

NaCl crystal are attracted to polar water molecules

• in solution are hydrated as several H2O molecules surround each

Attractions in Solutions

Interactions between solutes and solvents that • are similar in polarity will form a solution • are not similar will not form a solution

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When NaCl(s) dissolves in water, the reaction can be written as

H2O

NaCl(s) Na+(aq) + Cl(aq)

solid separation of ions

Equations for Solution Formation

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Solid LiCl is added to water. It dissolves becauseA. the Li+ ions are attracted to the 1) oxygen atom ( -) of water

2) hydrogen atom ( +) of water

B. the Cl ions are attracted to the 1) oxygen atom ( -) of water 2) hydrogen atom ( +) of water

Learning Check

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Solid LiCl is added to water. It dissolves because

A. the Li+ ions are attracted to the

1) oxygen atom ( -) of water.

B. the Cl ions are attracted to the

2) hydrogen atom ( +) of water.

Solution

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Two substances form a solution • when there is an attraction between the

particles of the solute and solvent

• when a polar solvent such as water dissolves polar solutes such as sugar and ionic solutes such as NaCl

• when a nonpolar solvent such as hexane (C6H14) dissolves nonpolar solutes such as oil or grease

Like Dissolves Like

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Water and a Polar Solute

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Like Dissolves Like

Solvents Solutes

Water (polar) Ni(NO3)2

CH2Cl2(nonpolar) (polar)

I2 (nonpolar)

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Will the following solutes dissolve in water? Why?

1) Na2SO4

2) gasoline (nonpolar)

3) I2

4) HCl

Learning Check

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Will the following solutes dissolve in water? Why?

1) Na2SO4 Yes, the solute is ionic.

2) gasoline No, the solute is nonpolar.

3) I2 No, the solute is nonpolar.

4) HCl Yes, the solute is polar.

Most polar and ionic solutes dissolve in water because water is a polar solvent.

Solution

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Solutions Continued

Properties of Solutions

Ethylene glycol is added to a radiator to form a aqueous solution that has a lower freezing point than water.

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Solutions

Solutions • contain small particles (ions or

molecules) that are uniformly dispersed in the solvent

• are not separated by filters or a semipermeable membrane

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Colloids

Colloids• contain large solute particles

that are uniformly dispersed in the solvent

• cannot be separated by filtration • can be separated by

semipermeable membranes

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Examples of Colloids

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Suspensions

Suspensions• have very large particles that

settle out • are separated by filters • must be stirred to stay

suspended

Examples: blood platelets, muddy water, and calamine lotion

Properties of Different Types of Mixtures

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Solutions Colloids, and Suspensions

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