AQUEOUS SOLUTIONS. Example The solution NaCl(aq) is sodium chloride NaCl(s) dissolved in water H 2 O(l) The solute is NaCl(s) and the solvent is H 2 O(l). A solution is a homogeneous mixture of a solute dissolved in a solvent. The solvent is generally in excess. Types of Solutions.
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The solution NaCl(aq) is
sodium chloride NaCl(s) dissolved inwater H2O(l)
The solute is NaCl(s) and the solvent is H2O(l)
A solution is a homogeneous mixture of a solute dissolved in a solvent.
The solvent is generally in excess.
Any solution can be made saturated, unsaturated, or supersaturated by changing the temperature.
The solubility of a solute in a given amount of solvent is dependent on the
and the chemical natures of the solute and solvent.
In general, as the temperature of a solution increases the solubility increases.
Increasing the solution temperature allows more sugar to go into solution. Therefore, it is an endothermic process (heat is on the reactant side).
In a few instances (e.g., Li2SO4 below) the solubility of the salt will decrease with temperature. This observation does not invalidate the above explanantion but rather suggests that several competing ideas need to be taken into account to fully understand chemical processes.
28g of anhydrous salt per 100g of water.
Reading graph: at 84 °C the solubility of potassium sulphate, K2SO4, is
22g per 100g of water.
Ex Q1: How much potassium nitrate will dissolve in 20g of water at 34 °C?
Ex Q2: At 25 °C 6.9g of copper sulphate dissolved in 30g of water, what is its solubility in g/100cm3 of water?
Ex Q3: 200 cm3 of saturated copper sulphate solution was prepared at a temperature of 90 °C. What mass of copper sulphate crystals form if the solution was cooled to 20 °C?
The solubility of a gas increases as the pressure increases.
Carbon dioxide, CO2(g) in carbonated drinks is dissolved in the solvent by increasing the pressure and also decreasing the temperature.
The rate of solution is a measure of how fast a substance dissolves. Some of the factors determining the rate of solution are:
Stir, and stir, and stir
Fresh solvent contact and interaction with solute
Add sugar to warm tea then add ice
Faster rate of dissolution at higher temperature
Grind the sugar to a powder
Greater surface area, more solute-solvent interaction
A polar solute will dissolve in a polar solvent but not in a nonpolar solvent. The adage "like dissolves like" is very useful.
Alcohol (polar substance) dissolves in water (polar substance)
Water (polar substance) does not dissolve in oil (nonpolar substance)
“Likes dissolve likes”
When two similar liquids - here water and methanol- are mixed, the molecules are intermingled. The mixture has a more disorderly arrangement of molecules than the separate liquids. It is this disordering process that largely drives solution formation.
Acids, bases and soluble ionic solutions are electrolytes.
Non-electrolyte:a substance that does not conduct electricity when dissolved in water.
Molecular compounds and insoluble ionic compounds are non-electrolytes.Electrolyte and Non-electrolyte
Strong Electrolyte -
all ions in solution
Weak Electrolyte -
molecules and ions in solution
all molecules in solution
CH3COOH(aq)← CH3COO-(aq) +H+(aq)
CH3OH(aq)Representation of Electrolytes using Chemical Equations
MgCl2(s) → Mg2+(aq) + 2 Cl-(aq)
A strong electrolyte:
Strong acids: HNO3, H2SO4, HCl, HClO4
Strong bases: MOH (M = Na, K, Cs, Rb etc)
Salts: All salts dissolving in water are completely ionized.
Stoichiometry & concentration relationship
NaCl (s) Na+ (aq) + Cl– (aq)
Ca(OH)2 (s) Ca2+(aq) + 2 OH– (aq)
AlCl3 (s) Al3+ (aq) + 3 Cl– (aq)
(NH4)2SO4 (s) 2 NH4+ (aq) + SO42– (aq)
HCl (g) H+ (aq) + Cl– (aq)
NaOH (s) Na+ (aq) + OH– (aq)
neutralization reaction: H+ (aq) + OH– (aq) H2O (l)
Explain these reactions
Mg(OH)2 (s) + 2 H+ Mg2+ (aq) + 2 H2O (l)
CaCO3 (s) + 2 H+ Ca2+ (aq) + H2O (l) + CO2 (g)
Mg(OH)2 (s) + 2 HC2H3O2 Mg2+ (aq) + 2 H2O (l) + 2 C2H3O2 – (aq) acetic acid
Spectator ions or bystander ions
Ag+ (aq) + NO3– (aq) + Cs+ (aq) + I– (aq) AgI (s) + NO3– (aq) + Cs+ (aq)
Ag+ (aq) + I– (aq) AgI (s) (net reaction)or Ag+ + I– AgI (s)
Silver halidesMetal sulfides, hydroxidescarbonates, phosphates
Alkali metals, NH4+nitrates, ClO4-, acetate
Mostly soluble ions
Ag+(aq) + NO3-(aq) + Na+(aq) + I-(aq) →
AgI(s) + Na+(aq) + NO3-(aq)Net Ionic Equation
Overall Precipitation Reaction:
AgNO3(aq) +NaI (aq) → AgI(s) + NaNO3(aq)
Complete ionic equation:
Ag+(aq) + NO3-(aq) + Na+(aq) + I-(aq) →
AgI(s) + Na+(aq) + NO3-(aq)
Net ionic equation:
Ag+(aq) + I-(aq) → AgI(s)
Write out the chemical reaction and name the precipitate.
CuSO4 (aq) + Na2S (aq) CuS (s) + Na2SO4 (aq)
Write out the net ionic equation.
Cu+2(aq)SO4-2 (aq) + 2Na+ (aq) + S-2(aq) CuS (s) + 2Na+ + SO4-2 (aq)
Cu+2(aq)+ S-2(aq) CuS (s)
Suppose potassium hydroxide reacts with magnesium chloride.
Write out the reaction and name the precipitate.
Write out the net ionic equation.How to write chemical equations
g solute + g solvent
moles of solute
volume in liters of solution
Units of Concentrations
amount of solute per amount of solvent or solution
Percent (by mass) =
Molarity (M) =
moles = M x VL
What is the percent of KCl if 15 g KCl are
placed in 75 g water?
%KCl = 15g x 100/(15 g + 75 g) = 17%
What is the molarity of the KCl if 90 mL of
solution are formed?
mole KCl = 15 g x (1 mole/74.5 g) = 0.20 mole
molarity = 0.20 mole/0.090L = 2.2 M KCl
Example 1:What is the concentration when 5.2 moles of hydrosulfuric acid are dissolved in 500 mL of water?
Step one: Convert volume to liters, mass to moles.
500 mL = 0.500 L
Step two: Calculate concentration.
C = 5.2 mol/0.500 L
What is the volume when 9.0 moles are present in 5.6 mol/L hydrochloric acid?
How many moles are present in 450 mL of 1.5 mol/L calcium hydroxide?
What is the concentration of 5.6 g of magnesium hydroxide dissolved in 550 mL?
What is the volume of a 0.100 mol/L solution that contains 5.0 g of sodium chloride?
How many Tums tablets, each 500 mg CaCO3, would it take to neutralize a quart of vinegar, 0.83 M acetic acid (CH3COOH)?
2CH3COOH(aq) + CaCO3(s) Ca(CH3COO)2(aq) + H2O + CO2(g)
moles acetic acid = 0.83 moles/L x 0.95 L = 0.79 moles AA
the mole ratio
mole CaCO3 = 0.79 moles AA x (1 mole CaCO3/2 moles AA)
= 0.39 moles CaCO3
mass CaCO3 = 0.39 moles x 100 g/mole = 39 g CaCO3
number of tablets = 39 g x (1 tablet/0.500g) = 79 tablets