Solutions II. Solubility curves Note that a typical solubility curve shows the total mass (in g) of...

Solutions IISolutions II

Solubility curvesSolubility curves

• Note that a typical solubility curve shows the Note that a typical solubility curve shows the total mass (in g) of a solute that will total mass (in g) of a solute that will completely dissolve in 100 g of water at a completely dissolve in 100 g of water at a given temperature.given temperature.

The solid line shows a The solid line shows a saturatedsaturated solution. solution. If the amount of solute dissolved is above If the amount of solute dissolved is above

that line, the solution is that line, the solution is supersaturatedsupersaturated. . If the amount of solute dissolved is below If the amount of solute dissolved is below

that line the solution is that line the solution is unsaturatedunsaturated..

Look at the graph in your notes.

AnalogyAnalogy Solving for solubility problems is like changing Solving for solubility problems is like changing

the serving size of a recipe for kool-aid.the serving size of a recipe for kool-aid.

The amount of water is 100mL (same as 100g)The amount of water is 100mL (same as 100g) Use your solubility graph Use your solubility graph

The amount of kool-aid powder is a value on the The amount of kool-aid powder is a value on the curve. curve.

However, depending on the temperature of your However, depending on the temperature of your water, the amount of powder can change.water, the amount of powder can change.

Not in your notes!

A. Using solubility curvesA. Using solubility curves• Whenever you obtain a value from a Whenever you obtain a value from a

solubility curve (the actual curve), it is solubility curve (the actual curve), it is always for a always for a saturatedsaturated solution and it solution and it describes:describes:

X g soluteX g solute

100 g H100 g H22OO• If your problem does If your problem does notnot have 100 g of have 100 g of

water, you will need to use a water, you will need to use a proportionproportion..• If your problem involves two different If your problem involves two different

temperatures, you will need to subtract.temperatures, you will need to subtract.• Remember, Remember, 1 g H1 g H22O = 1 mL HO = 1 mL H22OO

Example 1: I have a solution at 60Example 1: I have a solution at 60ººC with 80 g C with 80 g of sodium nitrate dissolved in 100 g of of sodium nitrate dissolved in 100 g of water. Is it saturated, supersaturated, or water. Is it saturated, supersaturated, or unsaturated?unsaturated?

HintHint: Is the intersecting : Is the intersecting point above, on, or point above, on, or below the line?below the line?

Below Below

Therefore...Therefore...UnsaturatedUnsaturated

Example 2: How much more sodium nitrate Example 2: How much more sodium nitrate could I add to the previous solution (80 g could I add to the previous solution (80 g NaNONaNO33 in 100g H in 100g H22O at 60O at 60ººC) to form a C) to form a

saturated solution?saturated solution?HintHint: How many : How many

more grams of more grams of solute are needed solute are needed from the from the intersecting point intersecting point to the line of to the line of saturation?saturation?

124g – 80g = 124g – 80g = 44 grams44 grams

= = ? g KCl ? g KCl

300mL H300mL H22OO

Ex: How many grams of potassium Ex: How many grams of potassium chloride will dissolve in 300 mL of water chloride will dissolve in 300 mL of water

at 50.0ºC?at 50.0ºC?

x 40g KCl40g KCl

100g H100g H22OO

120 g KCl120 g KCl per 300mL water per 300mL water

120 g KCl120 g KCl

Ex: I have a saturated solution with 9.2 g of solute Ex: I have a saturated solution with 9.2 g of solute dissolved in 10 g of water at 25dissolved in 10 g of water at 25ooC. C.

What is the solute?What is the solute?Hint: The solubility Hint: The solubility

curves only tell us curves only tell us the solubility of the solubility of solute in 100g of solute in 100g of water. water.

= = ? g ? g

100 g H100 g H22OO

9.2 g9.2 g

10 g H10 g H22OO

The solute is NaNOThe solute is NaNO33

92g

What is the solute?25°C

PracticePractice

1. I have a solution with 120 g of sodium nitrate dissolved in 1. I have a solution with 120 g of sodium nitrate dissolved in 100 mL of water at RT. Is it saturated, unsaturated, or 100 mL of water at RT. Is it saturated, unsaturated, or supersaturated?supersaturated?

2. a) How much potassium nitrate is dissolved in 100 g of 2. a) How much potassium nitrate is dissolved in 100 g of water at 50water at 50C to make a saturated solution? C to make a saturated solution? b)b) If I have 65 g of potassium nitrate dissolved in 100 g of If I have 65 g of potassium nitrate dissolved in 100 g of water at 50water at 50C, how much more could be added and have a C, how much more could be added and have a saturated solution? saturated solution?

3. What volume of water do I need to make a saturated 3. What volume of water do I need to make a saturated solution containing 1000. g of potassium chloride at 50solution containing 1000. g of potassium chloride at 50 C? C?

SupersaturatedSupersaturated

80g80g

80g – 65g =80g – 65g = 15g15g

X = 2500 g water X = 2500 g water

2.50 x 102.50 x 1033 g H g H22OO

1000 g KCl1000 g KCl = =

X g HX g H22OO40 g KCl40 g KCl

100 g H100 g H22OO


In this lesson we will learn how to In this lesson we will learn how to makemake and and calculatecalculate % and % and molarmolar solutions. solutions.

Chemists Chemists mustmust know how much stuff is know how much stuff is dissolved in a solvent so there are simple dissolved in a solvent so there are simple ratiosratios to to expressexpress the concentration that the concentration that everyone has agreed to use. everyone has agreed to use.

So these are just more definitions but So these are just more definitions but they’re written as equations.they’re written as equations.

Not in your notes!


If a chemist encounters a solution with an If a chemist encounters a solution with an unknown concentration of “X,” methods unknown concentration of “X,” methods have been devised to measure how much have been devised to measure how much “X” is present. “X” is present.

The concentration of “X” is then reported The concentration of “X” is then reported the way you will learn in this lesson.the way you will learn in this lesson.

Not in your notes!

Don’t lose sight of thisDon’t lose sight of this: Most of the : Most of the calculations we will do are just calculations we will do are just ratiosratios (dividing one number by another) turned (dividing one number by another) turned into into percentagespercentages. .

IT’S SIMPLE. IT’S SIMPLE. DON’T FREAK OUT!DON’T FREAK OUT!

Not in your notes!

A.A. VocabularyVocabulary

What is concentration?What is concentration?

1.1. The word The word concentrationconcentration is used to describe is used to describe how how much much solutesolute is dissolved is dissolved in a in a solventsolvent to make a to make a solutionsolution..

solventsolvent

solutesolute

into

A.A. VocabularyVocabulary What is concentration?What is concentration?

2.2. Qualitatively, we use the word “Qualitatively, we use the word “concentratedconcentrated” to imply ” to imply a a lot of dissolved solutelot of dissolved solute. .

3.3. A solution is “A solution is “dilutedilute” if it contains a relatively ” if it contains a relatively smallsmall amount of dissolved solute. amount of dissolved solute.

4.4. If a If a solution is solution is diluteddiluted, it means the original concentration , it means the original concentration value has been value has been loweredlowered by the addition of solvent to a by the addition of solvent to a portion of the original solution. portion of the original solution.

5.5. A concentrated solution that is used to make more A concentrated solution that is used to make more diluted solutions is often called a diluted solutions is often called a stockstock solution. solution.

Pictorial RepresentationPictorial Representation

B. Formulas for calculating and reporting B. Formulas for calculating and reporting Concentration as a PercentageConcentration as a PercentageThere are several ways to express concentration. There are several ways to express concentration.

They are They are RATIOSRATIOS of either: of either: mass to massmass to mass, , mass to volumemass to volume, or , or volume to volumevolume to volume..

*KEY POINT: Recognize the denominators. The represent the WHOLE SOLUTION, NOT just the solvent (this is a common student error!).

Percent ratios

% m/m = Mass (in grams) of SOLUTE

Mass (in grams) of SOLUTION

x 100

% m/v = Mass (in grams) of SOLUTE

Volume (in milliliters) of SOLUTION x 100

% v/v = Volume (in milliliters) of SOLUTE


• The denominatoris always SOLUTION.

• Always specify which ratio you are calculating

• Volumetric flaskor graduated cylinderis used for m/v orM solutions.

• Graduated cylinder isused for v/v solutions

Fix this inyour notes!!

So, when we talk about the mass or So, when we talk about the mass or volume of the SOLUTION, it’s either:volume of the SOLUTION, it’s either:

1.1. the sum of the the sum of the massmass values for the solute values for the solute and solvent (% m/m) and solvent (% m/m)

2.2. the sum of the the sum of the volumevolume values for the values for the liquidliquid solute and the solvent (% v/v) solute and the solvent (% v/v)

3.3. the the TOTALTOTAL volume volume that both the solute that both the solute and solvent together occupy (% m/v) and solvent together occupy (% m/v)

Example 1:Example 1:

A solution contains 7 g of NaCl in 165 g total.

X m/m =

7 g LiCl

165 g solutionx 100

= 4.24% NaCl by mass (m/m)

% m/m =

Mass (in grams) of SOLUTE

Mass (in grams) of SOLUTION x 100


A saline solution contains 3.5 g of NaCl in 62.5 mL of solution.

X m/v =3.5 g NaCl

62.5 mL solutionx 100

= 5.60% NaCl by mass (m/v)

% m/v =




How many milliliters of a 5.00% m/v solution will Dr. Poche make using 23.4 g of LiCl?

5.00% m/v =

23.4 g LiCl

X mL solutionx 100

X mL = 23.4 g LiCl

5.00= 468 mL solution

% m/v =



(X mL solution) (X mL solution)

5.00% m/v 5.00% m/v =

x 100

Example 4:Example 4:20 mL of alcohol is diluted with water to

a total volume of 65 mL. What is the percent alcohol by volume?

X v/v =

20 mL

65 mL solutionx 100

= 30.8% alcohol by volume (v/v)



Example 5:Example 5:What volume of ethanol is needed to

produce 120 mL of a 22.3% (v/v) ethanol solution?

22.3% v/v =

X mL

120 mL solutionx 100

= 26.8 mL ethanol by volume (v/v)



X mL = 22.3% v/v x 120 mL

100

Practice1. If 10 mL of pure acetone is diluted with water to a total

solution volume of 200 mL, what is the percent by volume of acetone in the solution? 10mL x 100 =200mL

2. A bottle of hydrogen peroxide is labeled 3.0% (v/v). How many mL of H2O2 are in a 400.0 mL bottle of this solution? 3% v/v = X x 100

400mL3. Calculate the grams of solute required to make 250 g of

0.10% MgSO4 (m/m). 0.10% m/m = X x 100

250g4.A solution contains 2.7 g CuSO4 in 75 mL of solution. What

is the percent (m/v) of the solution? 2.7 g x 100 = 75 mL

5.00% acetone (v/v)

X = 12.0mL H2O2

X = 0.250g MgSO4

3.60% (m/v)

Practice5.What volume of a 2.8% (m/v) glucose solution would you need

to deliver to a patient who needs 750 mg of glucose? 2.8% (m/v) = 750 mg glucose x 100 X = 2.68 x 104

mL X mL glucose solution

III.III. MOLARITY (RATIO OF MOLES OF MOLARITY (RATIO OF MOLES OF SOLUTE TO LITERS OF SOLUTION)SOLUTE TO LITERS OF SOLUTION)

*If you are given grams, convert it to moles *If you are given grams, convert it to moles using the MOLAR MASS of the substance. using the MOLAR MASS of the substance.

Molarity- unit abbreviation is M

Molarity =Moles of SOLUTE

Liters of SOLUTION

What is the molarity of a solution containing What is the molarity of a solution containing 12.3g of Na12.3g of Na22COCO33 in 675 mL of total volume? in 675 mL of total volume?

12.3 g Na2CO3 11 mol Na2CO3

= 0.172 M Na2CO3

.675 L

105.988 g Na2CO3

1


.675 L.675 LMolarity- unit abbreviation is M


Liters of SOLUTION

Molar Molar MassMass

A saline solution contains 0.90 g NaCl in exactly A saline solution contains 0.90 g NaCl in exactly 100 mL of solution. What is the molarity of the 100 mL of solution. What is the molarity of the solution? solution?

0.90 g NaCl 11 mol NaCl

= 0.154 M NaCl

.100 L

58.443 g NaCl

1


.100 L.100 L

Molarity- unit abbreviation is M


Liters of SOLUTION


How many grams of solute are present in 562 mL How many grams of solute are present in 562 mL of 0.24M Naof 0.24M Na22SOSO44? ?

0.135 mol Na2SO4 1 mol

Na2SO4= 19.2 g Na2SO4

142.042 g Na2SO41


.562 L.562 LMolarity- unit abbreviation is M


Liters of SOLUTION


.24 M = Moles

.562 L

Moles = 0.135 Na2SO4

Practice1. A solution has a volume of 2.0 L and contains 36.0 g of

glucose. If the molar mass of glucose is 180.156 g/mol, what is the molarity of the solution? 36.0 g glucose|1 mole glucose| 1 =

1 180.156 g/mol 2.0L2. How many moles of ammonium nitrate are in 335 mL of 0.425

M NH4NO3?

.425M NH4NO3 = X moles .335 L

3. How many grams of solute are in 250 mL of 2.0 M CaCl2

solution? 2.0 M CaCl2 = X moles X = 0.5 moles CaCl2

.250 L.5 moles CaCl2 | 110.986 g CaCl2 | =

1 mole CaCl24. Describe how you would prepare 250 mL of a 0.2 M NaOH

solution. Need 2.00g NaOH in 250mL of solution.2 M NaOH = X g NaOH

.250 L

0.100M glucose

X = 0.142 moles NH4NO3

55.5 g CaCl2

X = 0.0500g NaOH in 250mL of solution

IV.IV. DILUTIONS FROM A DILUTIONS FROM A STOCK SOLUTION USING MOLARITYSTOCK SOLUTION USING MOLARITY

*If you are given grams, convert it to moles *If you are given grams, convert it to moles using the MOLAR MASS of the substance. using the MOLAR MASS of the substance.

Dilutions (molarity)(M1 > M2 and V1 < V2)

M1V1

Moles ofStock used

Moles of dilutedsolution

M2V2 =

=


What volume of 2.5 M stock solution is needed What volume of 2.5 M stock solution is needed to make 75.0 mL of 0.0234 M NaCl? to make 75.0 mL of 0.0234 M NaCl?

M1V1 M2V2 =

VV1 1 = 0.0234M x 75.0mL= 0.0234M x 75.0mL

VV1 1 = = 0.0234M x 75.0mL0.0234M x 75.0mL

2.5 M2.5 M

VV11 = 0.702 mL = 0.702 mL

2.5 M2.5 M 2.5 M2.5 M

2.5 M x2.5 M x

Practice1.How many mL of a stock solution of 4.00 M KI

would you need to prepare 250.0 mL of 0.760 M KI? 4.00M * V1 = 0.760 M * 250.0 mLV1 = 0.760 M * 250.0 mL

4.00M2.What volume must you dilute to make 50.0 mL of

0.20 M KNO3 from 4.0 M KNO3? 0.20M * 50.0 mL = 4.0 M * V2

V2 = 0.20M * 50.0 mL 4.0M

3.What is the molarity of a solution formed when you add 200 mL of water to 50 mL of 5.0 M HCl? M1 * 200mL = 5.0M * 50mLM1 = 5.0M * 50mL

200mL

V1 = 47.5 mL of 4.00M KI

V2 = 2.5 mL of 0.20 M KNO3

M2 = 1.25M of HCl

A molar solution has a certain number of A molar solution has a certain number of moles of solute per one liter of solution.moles of solute per one liter of solution.

1.1. These solutions, where the VOLUME These solutions, where the VOLUME of the of the wholewhole solution is required, are solution is required, are best done in a piece of glassware best done in a piece of glassware called a 1 L called a 1 L volumetric flaskvolumetric flask. .

2.2. It only has It only has oneone volume mark but that’s volume mark but that’s all you need. It is marked on the neck all you need. It is marked on the neck at the volume the flask is calibrated to at the volume the flask is calibrated to hold.hold.

• By the way, that volume mark is By the way, that volume mark is only good for a given temperature, only good for a given temperature, 20 20 ooC. If you use the flask at any C. If you use the flask at any other temperature, your solution other temperature, your solution concentration will be off a little.concentration will be off a little.

V.V. Making a SolutionMaking a Solution

3.3. If given moles, convert to grams.If given moles, convert to grams.

4.4. Measure the appropriate mass and add it to the Measure the appropriate mass and add it to the volumetric flask.volumetric flask.

5.5. Next, add enough solvent to reach the Next, add enough solvent to reach the markmark (meniscus!) (meniscus!)

6.6. You now have a You now have a TOTALTOTAL volume of a 1 L for the volume of a 1 L for the solution.solution.

V.V. Making a SolutionMaking a Solution

SolutionConcentration

What is different between the glasses of Kool-aid?

Solution concentration can be described generally

Dilute - reduced in strength, weak, watered down.

Concentrated – stronger, pure. Has less water.

What’s the problem with just using dilute and concentrated as descriptions of the solution concentration?

Is solution B dilute or concentrated?

The terms dilute and concentrated are relative.

Scientists need a more precise way of referring to the concentration of a solution.

Concentrated Dilute

Solution A Solution B Solution C

Solution concentration can be described specifically

Do you remember the “mole” from Stoichiometry?

What is a mole?

How might you use it to describe the concentration of a solution?

Concentration can be represented by…

•Molarity

•Molality

•Percent by Mass

MolarityThe ratio of the moles of solute to the volume

of solvent in liters.

Symbol: MYou must be careful to label the molarity with a

capital M

Molarity (M) = Moles of solute

Volume in Liters of Solvent

How to read: 6M NaCl

Read: “6 molar solution of NaCl”Can be abbreviated 6M solution Be careful to label the molarity with a

capital M

How to make a 6M NaCl solution

(a) Add 6 moles NaCl to the volumetric flask.

How would you measure that?

6 moles NaCl 58.443 g NaCl

1 mole NaCl

= 351 g NaCl

How to make a solution using molarity (6M NaCl)

(b) Add dH2O to dissolve and mix the NaCl

(c) Fill the flask with dH2O until you reach the 1000mL line.

Solutions II. Solubility curves Note that a typical solubility curve shows the total mass (in g) of...

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