Exambusters Study Cards 13 Solutions

Molarity (State general equation)

The number of moles of solute in a liter of solution.

 

M=n/L

 

M= molarity;

n = moles;

L = liters

Solute

The substance dissolved in another (solvent).

Salt is the solute in salt water.

Solvent

A substance, usually a liquid, into which another substance (solute) is dissolved.

Water is the solvent in iced tea.

Solution (Give an example)

A liquid, gas, or solid phase containing two or more components uniformly dispersed.

 

e.g. air, coffee, saltwater

Calculate the molarity when 5 moles of NaCl is dissolved in 25 liters of water.

M = n/L

 

M = 5/25

M = 0.2M

Calculate the moles of NaCl in 5 liters of a 2 molar solution.

M = n/L

2 M = n/5 L

10 = moles of NaCl

Acid anhydride

Non-metallic oxides which, when reacted with water, form acid solutions.

e.g. CO2 + H2O → H2CO3

SO3 + H2O → H2SO4

Basic anhydride

Metallic oxides which, when reacted with water, form basic solutions.

e.g. Na2O + H2O → 2 NaOH

CaO + H2O → Ca(OH)2

Why is water a good solvent for ionic compounds?
Due to hydrogen bonding, water is polar. The negatively charged oxygen attracts a cation, and the positively charged hydrogen, an anion.
Solubility Curves
A curve for a given substance which shows how much dissolves in a given amount of solvent at different temperatures.
How do temperature and pressure affect the solubility of a solid?
Solubility usually increases with increasing temperature. Pressure has little effect.
How do temperature and pressure affect the solubility of a gas?
Solubility usually decreases with increasing temperature. Solubility in creases in direct proportion to an increase in pressure.
Which three factors affect the rate of solubility?

pulverizing

stirring

heating

What is a general rule for solubilities of polar and nonpolar compounds?

“Like dissolves like.” Ionic and polar solvents dissolve ionic, polar solutes.

e.g. Water dissolves salt.

 

Nonpolar solvents dissolve nonpolar solutes.

e.g. Acetone dissolves gasoline and cooing oil.

Solubility of nitrates, acetates, and chlorates in water.
All are soluble
Solubility of Na, K, and (NH4)+ compounds in water.
All are soluble.
Solubility of chlorides in water.
All chlorides are soluble, except Ag, Hg, Pb.
Solubility of sulfates in water.
All sulfates are soluble, except Pb, Ba, Sr, Ca
Solubility of carbonates, phosphates, sulfides, and silicates in water.
All insoluble, except Na, K, (NH4)+
Solubility of hydroxides (OH-) in water.
All insoluble except Na, K, (NH4)+, Ca, Ba, Sr
Hydrated ion
A dissolved ion which is surrounded by water molecules. It is attracted electrostatically to the polar water molecule.
Miscible

Two liquids which dissolve in each other.

e.g. water and alcohol

Immiscible

Two liquids which do not dissolve in each other.

e.g. oil and vinegar

Brownian Movement
When light is shone through a colloid, the individual zig-zag paths of the particles in the dispersing medium can be observed; like smoke in a dark theater.
Basic facts about Solutions

particle size less than 1 nanometer. 

Clear (may be colored)

)articles don’t settle

Can pass through membranes

Particles not visible

Basic facts about colloids

particles measure 1-1000 nanometers

Particles don’t pass through a membrane

Show Brownian movement and the Tyndall effect

Particles don’t settle

Clear

Pass through filter paper

Basic facts about Suspensions

No Brownian movement

Don’t pass through filter paper or a memebrane

Cloudy, but particles settle on standing

Particles visible with microscope or eye

Dilute
Small amount of solute in the solvent.
Concentrated
Large amount of solute in the solvent.
Saturated
In the presence of undissolved solute, the solution is holding all the solute possible at that temperature.
Unsaturated
More solute can be dissolved in the solvent at that temperature.
Supersaturated
Created by cooling a saturated solution. If cooled slowly, the solute stays dissolved. The amount of solute in the solution is greater than the solubility at a given temperature.
Write the equation for percent concentration of a solute in a solution (mass/mass).
% concentration = (gsolute/gsolution)(100%)
HOw many grams of NaCl are required to prepare 500 g of a 5% solution?
% Conc. = (gNaCl/gsolution)(100%) 5% = (x/500 g)(100%) 25 g NaCl = x
Molality

The number of moles of solute dissolved in 1 kg of solvent.

molality (m) = moles solute/kg solvent

Calculate the molality of 10 moles of H2SO4 dissolved in 4 kg of water.
molality = moles solute/kg solvent = 10/4 = 2.5 molal
Gram-equivalent weight
The amount of substance which reacts with or displaces one mole of H+ ions.
Normality
The number of gram-equivalent weights in a liter of solution.
Wire the equation for molarity changes related to diluting a solution.

(M1)(V1)= (M2)(V2)

 

M = molarity

V = Volume

10 liters of a 6 molar solution is diluted to 3 molar. What is the final volume?

(M1)(V1)= (M2)(V2)

(6)(10) = (3) (V2)

V2 = 20 L

Colligative Properties
Properties of solutions that depend primarily on the concentration of solute and not on the type of particle.
List three basic colligative properties of solutions.

vapor pressure lowering

boiling point elevation

freezing point depression

In H2O solutions how many °C is the freezing point depressed for each molal of solute?
1.86 °C for each molal of particles of solute
In H2O solutions how many °C is the boiling point elevated for each molal of solute?
0.51 °C for each molal of particles of solute
Hydrated crystal
A crystal that holds a definite proportion of water in its structure
Crystal
In a crystal structure, ions or atoms form a repeating pattern of unit cells.
List six basic types of unit cells which can make up crystal lattices.

Simple cubic

face-centered cubic

body-centered cubic

tetragonal

hexagonal

monoclinic

efflorescent

Hydrated crystals which lose their water of hydration on exposure to air at room temperature.

e.g. magnesium sulfate

deliquescent

Hydrated crystals which absorb water from the air and become wet.

e.g. calcium chloride and magnesium chloride

anhydrous crystal
A hydrated crystal which loses its water of hydration. The pure salt loses the crystal structure and crumbles to powder
Unit cell
The smallest portion of a crystal lattice that is repeated throughout the crystal
x

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