Solutions and Solubility

Lesson 1: Success Criteria

• By the end of today:• Describe different types of solutions using

scientific vocabulary.• Be able to properly make a solution of a

specific molar concentration.

Simulation – Salt & Solubility Phet

Which ones are solutions?

• Tea

• Stainless Steel Spoon

• Hand Sanitizer

• Hand Lotion

Solution Concentration

• Dilute:• A dilute solution is one which contains a

relatively small amount of solute compared to the amount of solvent.

• Concentrated• A concentrated solution contains a large

amount of solute compared to the amount of solvent.

• How can you make a concentrated solution more dilute?• Add solvent

• How can you make a dilute solution more concentrated?• Add solute

• Miscible:• When liquids can mix in a proportion to form a

homogeneous solution (eg. Ethanol and water)

• Immiscible:• When substances are added together they DO

NOT form a homogeneous mixture (eg. Oil and water)

• Saturated• One which contains the maximum amount of solute that can be

dissolved in a given amount of solvent at a particular temperature.

• Unsaturated• One which contains less than the maximum amount of solute that

can be dissolved in a given amount of solvent at a particular temperature.

• Supersaturated• A solution with more solute than a saturated solution

How can you tell if a solution is saturated, unsaturated or supersaturated?

• Saturated: If you add more solute it will not dissolve• Unsaturated: If you add more solute it will dissolve.• Supersaturated: If you add more solute it will crystallize

Success Criteria

• To be able to prepare aqueous solutions using both methods – dissolving a solid in a solvent and diluting a solution of known concentration.

Concentration

• Concentration is the amount of solute per unit of solution. It is expressed as a ratio of the amount of solute over the total amount of the solution.

• The different amounts of solute and solution can be expressed in different units. • Mass (µg, mg, g, kg) Volume (µL, mL, L)

• To find the concentration of an unsaturated solution:

Amount of solute x magnitude ratio Total Amt of Solution

Molar Concentration• The method of measuring

concentration used most often in chemistry is molar concentration. Eg. 3.0 mol/L HCl

Molar = Moles of solute (mol) Concentration Volume of the solution (L)

Known as Molarity and it’s unit is represented by M.

c = n .

V

Preparing Solutions in the Lab

• There are 2 ways to prepare a standard solution.

• Method 1 – make a solution from a solid solutec = n/V c = concentration (mol/L)

n = moles (mol)V = volume (L)

• Method 2 – dilute a concentrated solutionc1V1 = c2V2 c1 = initial

concentration V1 = initial volume

c2 = final concentrationV2 = final volume

Does the number of moles change?

Making a Solution in the Lab

1. Clean a stopper and volumetric flask with lab soap and rinse well with distilled water.

2. Fill the flask 1/3 full with distilled water.3. Use the volume of the volumetric flask to calculate how much

solute you need to add to it.4. Measure out the solute using one of the methods on the next

slide and transfer all the solute to your volumetric flask.5. Swirl the mixture in the flask until the solute is dissolved6. Add distilled water to the flask until the bottom of the meniscus

is just below the line on the neck of the flask.7. Use a wash bottle of distilled water to add water drop by drop

until the bottom of the meniscus is exactly on the line. 8. Stopper and invert the volumetric flask 20 times.9. Label your solution in mol/L. Include your name, the recipe and

the date prepared on the label.

Making a Solution in the Lab

When dissolving/dissociating a solid solute

When diluting a solution

i) Use c=n/V to calculate the mass of solute you need to add to the flask.

ii) Measure out the mass of solid into a small, clean, dry beaker using a scoopula and a balance.

iii) Add the solute in the beaker to the water in the volumetric flask using a funnel.

iv) Ensure all solid is transferred from the beaker to the flask by rinsing the beaker with distilled water and adding the rinse water to the volumetric flask at least 2 times.

i) Use C1V1 = C2V2 to calculate the volume of solute you need to add to the flask.

ii) Measure out the volume using a graduated or volumetric pipette and bulb and transfer it to the volumetric flask.

CalculationsMethod 1: Dissolving a Solid

1. Find the molar concentration of a 3.0L solution with 4 moles of NaCl dissociated in it.

2. How would you make a 2.0mol/L solution of C6H12O6 in a 50mL volumetric flask?

3. The molar concentration of sugar cane, C12H22O11 in a 355mL can of Coke is 0.32mol/L.

a) Find the number of moles of sugar in the can.

b) If you drank the whole can, what mass of sugar would you consume?

Making a Solution in the Lab

Method 2: Diluting a concentrated Solution

1. You are given a concentrated solution of 1.25 mol/L sodium chloride in water. What volume of this concentrated solution must you add to make 50mL of a 1.00mol/L NaCl solution.

2. You are given a 0.45mol/L concentrated sugar solution. How much concentrated sugar solution do you need to add to a 25mL volumetric flask to make a 0.25mol/L solution?

Recall – Net and Total Ionic Equations

Total Ionic Equation

Net Ionic Equation

KCl(aq) + AgNO3(aq) --> KNO3(aq) + AgCl(s)

Other Units of Concentration

Concentration

Stoichiometry in Solutions

• Success Criteria:• Be able to use stoichiometry to solve problems

involving solutions and solubility.

Example 1

• What is the minimum volume of 0.25mol/L MgCl2(aq) needed to precipitate all of the silver ions in 60.0mL of 0.30 mol/L solution of silver nitrate. Assume silver chloride is completely insoluble.

Example 2 – Limiting Reactant

• Calculate the mass of solid Ag2CrO4 that forms when 50.00mL of 0.100M AgNO3 reacts with 50.0mL of 0.150mol/L sodium chromate.

Learning Check

• What is the minimum volume of 0.25 mol/L MgCl2(aq) needed to precipitate all the silver ions in 60.0mL of a 0.30mol/L solution of silver nitrate. Assume silver chloride is completely insoluble.