Chapter 8 Solutions. Solutions and Other Mixtures Heterogeneous Mixtures: Does not have a fixed...

Chapter 8Solutions

Solutions and Other Mixtures

• Heterogeneous Mixtures: Does not have a fixed composition (Particles not distributed evenly)– Suspensions: particles are large and settle out

• Pulp in orange juice

• Particles may be filtered out


• Some mixtures of two liquids will separate– Oil, vinegar, and flavoring can be shaken

together to make salad dressing. But the dressing is a heterogeneous mixture.

• When the dressing stands for a few minutes, two layers form.

– The two liquids separate because they are immiscible, which means they do not mix

» Oil floats to the top since it is less dense» The process of pouring a less dense liquid off a

denser liquid is called decanting


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• Colloid: particles are too small to settle out– The color in Latex paint comes from solid

particles of colored pigments that are dispersed in water

– Particles small enough to pass through filter– Even though particles are small they still scatter

light that passes through he colloid (Tyndall effect)


• Other colloids:– Dispensing gas in a liquid

• Whipped cream

– Dispensing gas in a solid• Marshmallows

– Dispensing of water droplets in air• Fog

– Dispensing of small particles in air• smoke


• Some immiscible liquids can form colloids• Mayonnaise is a colloid made up of tiny droplets

of oil suspended in vinegar– Egg yolk coats the oil droplets so that they do not join

together and form a separate layer– Cream is a mixture of oil, proteins, and carbohydrate

dispersed in water. The lipid is coated with protein that acts as an emulsifier therefore spread throughout the mixture

– Emulsion: colloid in which liquids that usually do not mix are spread throughout each other

• One liquid is dispersed in the other


• Homogeneous mixtures: look uniform because the individual components of the mixture are too small to be seen

• Are solutions: all homogeneous mixtures are also solutions– Solute: substance that dissolves– Solvent: substance in which the solute dissolves

• Example: salt water


• Two or more liquids that form a single layer when mixed are miscible (one liquid is water)– Alcohol– Beer– Drinking alcohol


• Liquid solutions that do not contain water– Nail polish remover– Crude oil

• Distillation: process that separates miscible liquids


• Alloys: homogeneous mixture that is usually composed of two or more metals (solids can dissolve in other solids)– Metals melted to a liquid and mixed

– Have properties that the individual metals do not• Brass: solution of zinc dissolved in copper metal

• Bronze: solution of tin in copper metal

• Steel: metal solution that contains some non-metals (carbon)

How Substances Dissolve

Water

• Is V-shaped• Two hydrogen atoms are located

at the same end of the molecule, and oxygen is at the opposite end

– This arrangement allows oxygen to pull the shared electrons toward itself and away from the two hydrogen atoms

• The electron pairs are NOT shared equally, but spend more time in the vicinity of oxygen

• Because electrons are negatively charged, the oxygen end of the molecule is slightly more negative and the hydrogen end slightly more positive

– Because water has two poles of charge, it is a polar molecule, or dipole

COVALENT BONDS

Polar and Nonpolar Molecules

• Polar molecules orient themselves toward other dipoles or toward charged particles (such as ions and some proteins), and they play essential roles in chemical reactions in body cells

Polar and Nonpolar Molecules

• Different molecules exhibit different degrees of polarity, and we can see a gradual change from ionic to nonpolar covalent bonding– Extremes:

• Ionic bonds: complete electron transfer

• Nonpolar covalent bonds: equal electron sharing

– There are various degrees of unequal sharing in between

IONIC/POLAR/NONPOLAR

Hydrogen Bonds

• Weak attractions that form between partially charged atoms found in polar molecules

• Hydrogen bonds form when a hydrogen atom, already covalently linked to one electronegative atom (usually nitrogen or oxygen), is attracted by another electron-hungry atom, and forms a bridge between them

• Common between dipoles such as water molecules, because the slightly negative oxygen atoms of one molecule attract the slightly positive hydrogens of the other molecules

HYDROGEN BOND

Hydrogen Bonds

• Surface tension is due to hydrogen bonds between water molecules

• Although hydrogen bonds are too weak to bind atoms together to form molecules, they are important as Intramolecular bonds, which bind different parts of a single large molecule together into a specific three-dimensional shape– Some large biological molecules, such as proteins

and DNA, have numerous hydrogen bonds that help maintain and stabilize their structures


• Like dissolves like: means that a solvent will dissolve substances that have molecular structures that are like the solvent’s structure– Polar dissolve polar

• Many substance dissolve in water (universal solvent)– +/- charges attract charges of solute

– Nonpolar dissolves nonpolar• Nonpolar substances usually do not dissolve in water• Nonpolar molecules do not have partially negative and

positively parts because the electrons are distributed evenly over the whole molecule

• Nonpolar solvents must be used to dissolve nonpolar materials– Oil based paint must be dissolved by nonpolar solvent


• The dissolving process:– Kinetic theory of matter states that molecules

are always moving– The energy transferred from the solvent to the

solute, as well as the attractive forces between the solvent and solute molecules, causes molecules at the surface of the substance to dissolve


• The dissolving process:– Solutes with a larger surface area dissolve faster

• Small pieces of a solid dissolve faster than large pieces of the same solid (small pieces have a larger surface area)

– Cube of 1 cm on each edge» Each face has an area of 1 cm2

» 6 surfaces= total surface area of 6 cm2

– Large Cube broken down to smaller cubes of 0.1 cm on each edge

» Each face has an area of 0.01 cm2

» 6 surfaces= total surface area of 0.06 cm2

» Total surface of 1,000 cubes is 1,000 x 0.06cm2 = 60 cm2

» Which is 10 times the surface area of the larger cube


• Surface area to volume ratio

• SA/Vol


• The dissolving process:– Stirring or shaking helps solids dissolve faster– Solids dissolve faster when the solvent is hot


• Solutes affect the physical properties of a solution– Boiling point of water is 1000C and the freezing

point is 00C• If you add salt (NaCl) the boiling point will increase

and the freezing point will decrease– Cooking and melting winter ice

• Ethylene glycol (antifreeze) in car– Raising boiling point and lowers freezing point

Solubility and Concentration

• Solubility of a substance is the maximum mass of a solute that can dissolve in 100 g of solvent at a certain temperature and standard atmosphere pressure– Different substances have different solubilities

in water• Depends on the on the strength of the forces acting

between the solute particles and the strength of the forces acting between water molecules and solute particles


• How much of a substance is in a solution?– Concentration: the amount of a particular substance in a

given quantity of a mixture, solution, or ore:• Not quantitative terms:

– Concentrated: large amount of solute

– Dilute: small amount of solute

– Saturated: dissolved solute is in equilibrium with undissolved solute. So, if you add more solute, it just settles to the bottom of the container

» Heating can dissolve more solute (supersaturated)

– Unsaturated: least than the maximum amount of solute


• Temperature and pressure affect the solubility of gases

• Temperature: – Unlike solids, gases are less soluble in warmer water

• Fish???

• Pressure:– High: more gas dissolves– Low: less gas dissolves– Example:

• Carbonated drink• Scuba diver (bends)


• Concentration of solutions– Terms concentrated, dilute, saturated, and

unsaturated do not reveal the quantity of dissolved solute

– One of the most common ways of expressing the concentration of a solution is molarity

• Molarity is expressed as moles of solute per liter of solution


• Molarity = moles of solute/liters of solution

• M = mol/L

• Example: a 1.0 M is read as one molar solution– A 1.0 M solution of NaCl contains 1.0 mol of

dissolved NaCl in every 1.0 L of solution


• Calculate the molarity of sucrose, C12H22O11, in a solution of 124 g of solute in 0.500 L of solution

• Moles C12H22O11 = mass C12H22O11/molar mass C12H22O11

• Molarity = moles C12H22O11 / liters of solution

• Molar mass C12H22O11= 342 g

• Moles C12H22O11= 124 g / 342g/mol = 124g x 1mol/342g = 0.362 mol

• Molarity of solution=0.362 molC12H22O1 1 / 0.500 L solution=0.724 M

Chapter 8 Solutions. Solutions and Other Mixtures Heterogeneous Mixtures: Does not have a fixed...

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