Solutions2587

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Solutions

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Solute

Solvent

Solution

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How much I have to add to have a GOOD lemonade?

Is it concentrated?

Is it diluted?

How would you prepare a lemonade?

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Definitions

SolutionHomogeneous mixture where particles are

uniformly distributed throughout.

SoluteThe substance that dissolves in a solvent

SolventThe substance in which a solute dissolved

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Solutions

When water is a solvent, the solution is aqueous.

Solvents may be gases: air is a solution of nitrogen, oxygen, argon, and other gases.

Steel is an alloy, solution of one solid dissolved in another solid are solutions of various metals.

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SolubilityThe maximum amount of solute that

dissolves in a fixed quantity of a particular solvent.

SolubleCapable of being dissolved.

Salt is soluble in water

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Solubility Terms

MiscibleTwo liquids that are soluble in each other. If they are soluble in any proportion, they

are said to be completely miscible.Liquids that are partially soluble are said to

be partially miscibleImmiscible

Liquids that are not soluble when mixed.

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Solubility Terms

Insoluble. When a substance does not appear to dissolve in a solvent.

A concentrated solution has a relatively large amount of solute for given quantity of solution.

A dilute solution has a smaller amount of solute for a given quantity of solution.

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Insert figure 14.4

Oil is Not Soluble in Water

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Ionic Solubility

Water will dissolve many ionic compounds (salts).

When salts dissolve in water:1. The ionic forces holding ions together are

broken.2. The attractive forces holding some of the

water molecules together are broken.3. Ions must interact with the solvent molecules

to form attractive forces.

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Ionic Solubility

The process in which water molecules surround the ions is called hydration.

For other solute/solvent interactions, this process is called solvation.

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Insert figure 14.3

Dissolving an Ionic Compound in Water

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Polarity

The geometry of atoms in polar molecules is such that one end of the molecule has a positive electrical charge and the other side has a negative charge.

Non-polar molecules do not have charges at their ends. Mixing molecules of the same polarity usually results in the molecules forming a solution.

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Solubility

Like dissolves like.Non-polar solutes dissolve in non-polar

solvents (like oil, thinner, soaps).

Polar solutes dissolve in polar solvents (water, alcohol, acids).

Hydrogen bonding between solute and solvent molecules plays an important role.

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Electrolytes

Substances that give ions when dissolved in water are called electrolytes.

They can be divided into acids, bases, and salts, because they all give ions when dissolved in water.

These solutions conduct electricity due to the mobility of the positive and negative ions, which are called cations and anions respectively..

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Electrolytes

Strong electrolytes completely ionize when dissolved, and no neutral molecules are formed in solution

Small fractions of weak electrolytes' molecules ionize when dissolve in water. Some neutral molecules are present in their solutions. For example, ammonia, NH4OH, carbonic acid, H2CO3, acetic acid, CH3COOH, and most organic acids and bases are weak electrolytes.

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Solubility Equilibria Most solutes have a limited solubility in a given

solvent. When more solute is present than the solubility

limit, a dynamic equilibrium is established:

solute + solvent solution

A solution of this type is said to be saturated.

A solution that contains less solute than the solubility limit is unsaturated.

dissolving

crystallizing

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Effects of Temperature on Solubility Most solids become more soluble as

temperature increases. (There are some exceptions.)

If a saturated solution is cooled, with solid present, more solid will precipitate until equilibrium is re-established.

If a saturated solution is cooled with no solid present, sometimes precipitation does not occur immediately. The solution is said to be supersaturated.

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Factors affecting solubility

Temperature (more temperature more solubility, in gases is opposite)

Pressure (more pressure more solubility, in gases is opposite).

Size of the solute (the smallest the solute is cut the easy to dissolve)

Nature of solute and solvent (polarity)

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Concentration

The concentration of a solution is the amount of solute dissolved in a certain quantity of solvent.

One measure of concentration is molarity M.

M = (# mol solute)/1 Liter of solution

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Molarity Problem

Tell how to prepare 250 mL of a 3.00 M solution of NaCl. M= # moles / Liters

1. Convert mL to L: 1L → 1000 mL x → 250 mL

2. Convert grams to mol with Molar Mass Na 23.0 + Cl 35.45 = 58.45 g/mol 58.45 g → 1 mole x → 3 moles (3M)

3. Convert grams to volume 175.35 g → 1 L x → 0.250 L|

g.mole

g.mole35175

1

45583

LmL

LmL250.0

1000

1250

gL

gL84.43

1

35.175250.0

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Preparing solutions of a given molarity

The plan for solving the above problem was:

mL L moles grams

To actually prepare the solution, 250 mL of 3.00 M NaCl:

1. Transfer 43.8 g of NaCl to a 250 mL volumetric flask partly filled with distilled water.

2. Shake to dissolve.

3. Add enough water to the flask to reach the mark

4. Stopper the flask and invert several times to mix thoroughly.

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Another Molarity Problem

How many mL of 12.00 M HCl solution are required to deliver 0.500 mol?

L = moles/M = (0.500 mol)/(12.00 mol/L)

=0.0417 L

0.0417L x 1000 mL/L = 41.7 mL

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Percent by Volume [%(v/v)]

Percent by Volume = [(volume solute)/(volume solution)]x100% Calculate the percent by volume alcohol

prepared by mixing 15.0 mL with enough water to make a total volume of 50.0 mL.

Percent by volume =

[(15 mL)/(50 mL)] x 100 = 30%(v/v)

50 mL → 100%

15 mL → x%30

50

%10015

mL

mL

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Percent by mass [%(w/w)]

Percent by mass

= [(mass solute)/(total mass of solution)]x100%

=[(g solute)/(g solute + g solvent)] x 100%

How many g of NaCl are required to prepare 100 g of a 5.0% solution?Mass solute = (percent/100)x(total mass)

= (5/100)x100 g = 5.0 g NaCl

100g →100%

x → 5% gg

5%100

100%5

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Preparation of Solutions by Dilution

Calculate the volume of 10.0%(v/v) ethanol

require to prepare 500 mL of 5.00% ethanol.

V1 C1 = V2 C2

Desired [ ]

C1 = 10.0, V2 = 500 mL, C2 = 5.00

V1 = V2C2/C1 = (500mL)(5.00%)/(10.0%)

= 250 mL

mLmL

C

CV250

%10

%5500

2

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Colligative Properties

Properties of liquids change when solutes are dissolved in them: boiling point is raised melting point is decreased The higher the concentration of solute particles, the

greater the effect.

Colligative Properties are properties of solutions that depend on the number of dissolved solute particles.

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Counting Particles

A solution of 1.00 L of a 1.00 M solution of glucose contains 6.022 x 1023 particles of glucose molecules.

But a solution of 1.00 L of a 1.00 M solution of NaCl contains 2x6.022x1023

particles because of ionization.The freezing point depression of 1.0 M

NaCl is almost twice that of 1.0 M glucose.

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Colloids

The temporary dispersion of one substance in another is a mixture called a suspension.

Part of the mixture will settle out from the other part or can be separated by filtration.

Colloids or colloidal dispersions are defined as mixtures having a particle size of 1.0 nm - 100 nm.

Colloids appear milky or cloudy. They scatter light by the Tyndall effect.

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Colloids

There are 8 different types of colloids based on the particles and the phase of the dispersal agent.

Some examples are foams and emulsions.

Colloids are stabilized by emulsifying agents such as soap or bile salts.

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Osmosis and Dialysis

Certain materials are: Permeable: allow water and solvents to pass through. Impermeable: do not allow solvents to pass. Semipermeable: material which allows solvent molecules to

pass, but not solute molecules. The process of solute molecules passing through a

semipermeable membrane is called osmosis. If small ions and molecules pass through the

membrane with the solvent, but colloidal particles are retained the process is called dialysis.

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Insert figure 14.16

A Semipermeable Membrane

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Osmosis The pressure required to prevent the flow of

solvent from the less concentrated side to the more concentrated side of a membrane is called the osmotic pressure.

Isotonic solutions is one that has the same osmotic pressure as the fluid in a living cell.

Hypotonic solutions have a lower concentration than inside the cell. Water flows from a solution into a cell.

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Osmosis in Cells

The rupture of a cell by hypotonic solutions is called plasmolysis (or hemolysis in the case of red blood cells)

Hypertonic solutions contain a greater concentration of particles than the fluid in cells. Water will flow from the cells to the solution.

This process is called crenation.