II
III
I II. ConcentrationII. Concentration
Ch. 13 & 14 - SolutionsCh. 13 & 14 - Solutions
What is different between the glasses of Kool-aid?
What is different between the glasses of Kool-aid?
Solution concentration can be described generally
Solution concentration can be described generally
Dilute - reduced in strength, weak, watered down.
Concentrated – stronger, pure. Has less water.
What is the problem with just using dilute and concentrated as descriptions of the solution concentration?
What is 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
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?
A. ConcentrationA. Concentration
The amount of solute in a solution.
Describing Concentration
• % by mass - medicated creams
• % by volume - rubbing alcohol
• ppm, ppb - water contaminants
• molarity - used by chemists
• molality - used by chemists
MolarityMolarity
The ratio of the moles of solute to the volume of solution in liters.
Molarity (M) =
Moles of solute
Volume in Liters of Solution
How to read MolarityHow to read Molarity
6.0 M NaClRead: “6 molar solution of NaCl”Can be abbreviated 6M solution You must be careful to label the
molarity with a capital M so that it is not confused with m for molality.
How to make a 6M NaCl solution using molarity
How to make a 6M NaCl solution using molarity
(a) Add 6 moles NaCl to the volumetric flask. How would you measure that?
6 molesNaCl 58.443 g NaCl
1 mole NaCl
= 351 g NaCl
How to make a 6M NaCl solution using molarity
How to make a 6M NaCl solution using molarity
(b) Add distilled or deionized H2O to dissolve and mix the NaCl
(c) Fill the flask with dH2O until you reach the 1000mL line.
Types of Calculations with Molarity:
Types of Calculations with Molarity:
1. Finding concentration of a solution.
2. Finding the mass of solute needed.
3. Finding the volume of solution made.
Finding ConcentrationFinding Concentration
Antifreeze is a solution of ethylene glycol, C2H6O2 in water. If 4.50 L of antifreeze contains 27.5 g of ethylene glycol, what is the concentration of the solution?
27.5 g C2H6O2
62.08 g C2H6O2
1 mol C2H6O2
4.5 L
= 0.0984 mol/L or
0.0984 M C2H6O2
Finding Mass Finding Mass
What mass of sodium carbonate, Na2CO3,
is present in 50 ml of a 0.750M solution?
50 ml 1 L
1000 mL
0.750 mol
1 L 1 mol Na2CO3
105.99 g Na2CO3
= 3.97 g Na2CO3
Conversion Factor
Finding VolumeFinding Volume
What volume of 1.50 mol/L HCl solution contains 10.0 g of hydrogen chloride?
10.0 g HCl 1 mol HCl
36.46 g HCl 1.50 mol
1 L
= 0.183 L or 183 mL
Conversion Factor
Practice Problems
Practice ProblemsPractice Problems
1. A 0.750 L aqueous solution contains 90.0 g of ethanol, C2H5OH. Calculate the molar
concentration of the solution in mol/L.
Practice ProblemPractice Problem
2. What mass of NaCl are dissolved in 152 mL of a solution if the concentration of the solution is 0.364 M?
Practice ProblemPractice Problem
3. What mass of dextrose, C6H12O6 is dissolved in 325 mL of 0.258 M solution?
Practice ProblemPractice Problem
4. A mass of 98 g of sulfuric acid, H2SO4, is dissolved in water to prepare a 0.500 M solution. What is the volume of the solution?
Practice ProblemPractice Problem
5. A solution of sodium carbonate, Na2CO3, contains 53.0 g of solute in 215 mL of solution. What is its molarity?
Practice ProblemPractice Problem
6. What is the molarity of a solution of HNO3 that contains 12.6 g of solute in 5.00 L of solution?
B. MolalityB. Molality
solvent ofkg
solute of moles(m)molality
mass of solvent only
1 kg water = 1 L waterkg 1
mol0.25 0.25m
B. MolalityB. Molality
Find the molality of a solution containing 75 g of MgCl2 in 250 mL of water.
75 g MgCl2 1 mol MgCl2
95.21 g MgCl2
= 3.2m MgCl2
0.25 kg water
kg
molm
B. MolalityB. Molality
How many grams of NaCl are req’d to make a 1.54m solution using 0.500 kg of water?
0.500 kg water 1.54 mol NaCl
1 kg water
= 45.0 g NaCl
58.44 g NaCl
1 mol NaCl
kg 1
mol1.5 1.5m
Practice ProblemPractice Problem
What is the molality of a solution made
from 2.4 moles of NaCl and 0.80 kg of
water?
Practice Problem Practice Problem
What is the molality of a solution made
from 63 g of HNO3 in 0.50 kg of water?
Practice ProblemPractice Problem
How much water is needed to make a 0.50 m solution from 3.2 g of NaCl?
Practice ProblemsPractice Problems
What mass of CH3OH is needed to add to
1.20 kg of water to make a 3.00 m
solution?
2211 VMVM
C. DilutionC. Dilution
Preparation of a desired solution by adding water to a concentrate.
Moles of solute remain the same.
C. DilutionC. Dilution
What volume of 15.8M HNO3 is required to make 250 mL of a 6.0M solution?
GIVEN:
M1 = 15.8M
V1 = ?
M2 = 6.0M
V2 = 250 mL
WORK:
M1 V1 = M2 V2
(15.8M) V1 = (6.0M)(250mL)
V1 = 95 mL of 15.8M HNO3
Dilution PracticeDilution Practice
Water is added to 200. mL of a 2.0 M
solution of CaCl2 to increase the volume of
the solution to 400. mL. What is the new
concentration?
Dilution PracticeDilution Practice
To what volume must 1.0 L of a 6.0 M
solution of HCl be diluted in order to
prepare a 0.2 M solution?
D. Preparing SolutionsD. Preparing Solutions
500 mL of 1.54M NaCl
500 mLwater
45.0 gNaCl
• mass 45.0 g of NaCl• add water until total
volume is 500 mL• mass 45.0 g of NaCl• add 0.500 kg of water
500 mLmark
500 mLvolumetric
flask
1.54m NaCl in 0.500 kg of water
D. Preparing SolutionsD. Preparing Solutions
250 mL of 6.0M HNO3 by dilution
• measure 95 mL of 15.8M HNO3
95 mL of15.8M HNO3
water for
safety
250 mL mark
• combine with water until total volume is 250 mL
• Safety: “Do as you oughtta, add the acid to the watta!”
Solution Preparation LabSolution Preparation Lab
Turn in one paper per team. Complete the following steps:
A) Show the necessary calculations.
B) Write out directions for preparing the solution.
C) Prepare the solution. For each of the following solutions:
1) 100.0 mL of 0.50M NaCl
2) 0.25m NaCl in 100.0 mL of water
3) 100.0 mL of 3.0M HCl from 12.1M concentrate.
500.O ml of 0.50 M NaCl500.O ml of 0.50 M NaCl
Remember: 0.50 M = 0.50 mole/1 Liter Convert 0.50 moles to grams of NaCl 0.50 mole NaCl = 29.23 grams but this is in 1 liter Figure out how much you need for 0.1 L Set up a proportion. 29.23g = x
1 L 0.5 L X = 14.62 g, measure this amount on a balance
and add to a volumetric flask. Then fill with distilled water to the 500 ml mark.
0.25 m NaCl in 100 ml of water 0.25 m NaCl in 100 ml of water
Remember: 0.25 m = 0.25 moles/1kg of water Convert 0.25 moles to grams. 0.25 moles = 14.61 grams – this is in 1 kg of water. Figure out how much you need for 0.100 kg of water. 1kg = 1L Set up a proportion. 14.61 g = x
1 kg 0.100 kg X = 1.461 g, measure this amount on a balance and add to a
flask. Then measure out 100 ml of water in a graduated cylinder.
Add this volume of water to the flask containing the NaCl.
How do you make a 100.0 mL solution with a concentration of 3.0 M HCl from 12.1M concentrate
How do you make a 100.0 mL solution with a concentration of 3.0 M HCl from 12.1M concentrate
This is a dilution problem because you have 2 different concentrations.
Solve for the first volume:
(12.1)(V1) = (3.0)(0.100)
V1 = 0.025 L or 25 mL
Measure out 25 mL of HCl in a graduated cylinder In a 100 mL volumetric flask, add about 50 mL of water then
slowly pour the 25 mL of HCl into the flask. Then add the remaining volume of water to the 100 ml mark.
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