Solubility

Solubility

​Take a moment to read through the summary and ask questions if any part is confusing.

Multiple Choice

Which of the following is an ionic compound?

• KCl

• CH₄

• CO₂

• H₂O

Categorize

Options (6)

NaCl

CuCl₂

C₆H₁₂O₆

O₂

CH₄

NaNO₃

Organize these options into the right categories

Ionic

Covalent

​Solutions

​Solutions are made when you dissolve a chemical called solute into another chemical called the solvent.

​Ionic vs Covalent (Molecular) Dissolution

​Explore this simulation to compare how salt (NaCl, ionic) and sugar (C12H22O11, covalent) 

• Ionic compounds dissociate into individual ions.

• Covalent compounds form molecular solutions, where atoms remain part of molecules.

Draw

Draw how LiF would dissolve in water.

Draw

Draw how CO₂ would dissolve in water.

​Electrolytes

​Electrolytes: Electrolytes are solutions that conduct electricity. Materials are only able to conduct electricity if there have:

• Freely moving cations (ie, Ca²⁺, NH⁴⁺)

• Freely moving anions  (ie, Cl^-, SO₄^2-)

• Freely moving electrons (negatively charged)

Categorize

Options (10)

LiCl

FeCl₃

Soluble Ionic Compound

Conducts electricity.

O₂

H₂O

Does not conduct electricity.

Covalent compounds.

Sort the following:

Electrolyte

Non-Electrolyte

​Electrolytes

• Soluble ionic compounds are electrolytes, while most covalent compounds are non-electrolytes (except weak acids, covered in next unit).

• Ionic(aq) = electrolyte

• Anything else = nonelectrolyte
  
  

​Concentration

In general the concentration is measured as:

​Concentration Terminology

​Concentration Terminology: 

• Dilute Solution (Unsaturated): Small amount of solute in a large amount of solvent. 

• Concentrated Solution (Unsaturated): Lots of solute in a small amount of solvent (all dissolves).

​Concentration Terminology

Saturated Solution: The maximum amount of solute dissolved in a given amount of solvent at a given temperature. To make a saturated solution you add more solute than can be dissolved.

Multiple Choice

Numbering from the left, which is most dilute?

• 1

• 2

• 3

• 4

• 5

Multiple Choice

How do you know if a solution is saturated?

• When you see some undissolved solute at the bottom that doesn't disappear if you stir it.

• When it is darker colored.

• When it is transparent.

• When you can dissolve more solute if you stir it.

Concentration Formula

​To calculate concentration we can use this formula:

Concentration Formula

What is the molarity of a NaCl solution in which 0.17 mol of NaCl is dissolved to make a 2 L solution?

Concentration Formula

​Finding Concentration of a Saturated Solution

​Connection to Solubility

​Once we write a balanced dissociation equation, we can use the coefficients to calculate the concentration of the ions if we assume the solute fully dissociates.

​1NaCl → 1Na⁺(aq) + 1Cl^-(aq) 

For every 1 NaCl dissolved,
1 Na+ and 1Cl- are produced.

​CaCl₂ → Ca²⁺(aq) + 2Cl^-(aq)

For every 1 CaCl₂ dissolved,
1 Ca²⁺ and 2 Cl^- are produced.

​Connection to Solubility

​Solubility Rules

While all substances have solubility to a certain extent, the course defines soluble if it will form a 0.1 M or higher solution at 25 degrees Celsius. Below that = insoluble.

​Solubility Rules

​Solubility Rules

​You try #38 to 48.

​Precipitation Reactions

​Double displacement reactions that produce a precipitate. For a precipitation reaction to occur, 2 conditions must be met:

1. Both reactants must be soluble ionic compounds

2. At least 1 of the new ionic compounds produced must be insoluble.

​Step 1: Write out both reactants, using criss-cross method to predict formulas if given names only.

Step 2: Check that both reactants are soluble. If not, stop here as there will be no reaction when mixed.

Step 3: Swap the cations and ions using the criss-cross method to predict the formulas of two new ionic compounds.

Step 4: Check the solubility, at least one must be insoluble (precipitate).

​Practice

​Practice

​You Try #57 - 72

​Complete Ionic Equations

​Complete ionic equations are when you write soluble ionic compounds as separate ions rather than as a compound:

​Spectator Ions: In a full ionic equation, soluble ions that appear as both products and reactants are called spectator ions. This is because they do not participate in a reaction producing a precipitate.

​Practice

​Write complete ionic equations for the following & identify the spectator ions.
Hint: Ensure everything is balanced!

​You try #73 - 77

​Filtration

​Precipitation reactions can be used to separate soluble ions from one another. By making one ion precipitate, we can then filter accordingly. 

1. The filtrate will contain the soluble ion(s)

2. The residue caught in the filter will hold the insoluble ion.

​Filtration

​Filtration Experiment

​Note: it won't go perfectly, but gives the idea.

​You Try #78 - 87, 111 - 119

​Practice Separation

​Connecting to Equilibrium

​As saturated solutions are at equilibrium, Le Chatelier’s Principle can be applied to predict which side will be favored (shifted to) if a stress is added.

​No effect

left

right

right

​Experiment

​Experiment

​You Try #88 to 110

​Solubility Product Constant

​When a saturated solution is at equilibrium, we can calculate an equilibrium constant as shown below:

​You Try: Problems 123 to 128

​Magnitude of Ksp

They are summarized in the data booklet. Just as with the equilibrium constant:

• ​a large K_sp means equilibrium lies to the right (the substance is highly soluble).

• a small K_sp means equilibrium lies to the left (the substance is insoluble)

You Try #49 to 56

​Step 1: Write the dissociation equation & balance it.

Step 2: Write the Ksp expression.

Step 3: Substitute in the concentrations, taking into account the mole ratios.

​Calculating Ksp from Solubility

​Try Problems
129 to 143

​Calculating Solubility from Ksp

​Step 1: Write the dissociation equation & balance it.

Step 2: Let x = concentration of each ion & multiply each by coefficient.

Step 3: Write the Ksp expression & substitute in the concentrations (in terms of x)

Step 4: Evaluate using algebra.

​You Try 145 to 152

​Connecting to Mass

​In the previous question, calculate the mass of Ag₂CrO₄ dissolved in 500 mL of saturated solution (in other words, maximum mass that can be dissolved). Continue steps of previous question...

Step 5: Multiply [ CrO₄^2- ] by volume to get moles. n=cV

Step 6: Moles of CrO₄^2- = moles Ag₂CrO₄ due to 1:1 mole ratio.

Step 7: Convert to mass using m = nM

​You Try: 144, 161

​Dilutions

To calculate new concentrations after chemicals are combined, we use this equation:

​Trial Ion Product (Q_sp)

Q_sp is like Q for K. Q_sp uses non-equilibrium concentrations, while Ksp uses equilibrium concentrations. The expressions are the same and just like with Q and K, we compare the values to determine which side the system will shift towards.

Multiple Choice

If K_sp = 1.4 x 10^-12, will a precipitate form if Qsp is found to be 1.4 x 10^-5?

• Yes

• No

​You Try: 153 to 160

​You Try: 161 to 168

​Sample Problem

​What is maximum [Ca²⁺] in a 0.10 M solution of Na₂SO₄ without a precipitate forming?

Step 1: Determine what precipitate forms.

Step 2: Write the dissociation equation & balance it.

Step 3: Substitute in the Ksp (from data booklet), the given concentration & assign “x” to the unknown.

Step 4: Use algebra to solve