II

III

I II. Solution Concentration

(p. 480 – 486)

Ch. 16 – SolutionsCh. 16 – Solutions

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

B. Percent SolutionsB. Percent Solutions

Percent By Volume (%(v/v))

• Concentration of a solution when both solute and

solvent are liquids often expressed as percent by

volume

100solution ofvolume

solute ofvolume (%(v/v))Volume by Percent

total combined volume

substance being dissolved

B. Percent SolutionsB. Percent Solutions

Find the percent by volume of ethanol (C2H6O) in a 250 mL solution containing 85 mL ethanol.

85 mL ethanol

250 mL solution = 34%

ethanol (v/v)

Solute = 85 mL ethanolSolution = 250 mL

% (v/v) = x 100

B. Percent SolutionsB. Percent Solutions

Percent By Mass (%(m/m))

• Concentration of a solution when solute is solid

sometimes expressed as percent by mass

100solution of mass

solute of mass(%(m/m)) Massby Percent

total combined volume

substance being dissolved

B. Percent SolutionsB. Percent Solutions

How much glucose should you use to make 2000. g of a 2.8% (m/m) solution in water?

unknown g glucose

2000. g solution= 56.00 g

glucose

Percent (m/m) = 2.8%Solution = 2000. g

2.8 = x 100

C. MolarityC. Molarity

Concentration of a solution most often

used by chemists

solution of liters

solute of moles(M)Molarity

total combined volume

substance being dissolved

C. MolarityC. Molarity

2M HCl

L

molM

nsol' L 1

HCl mol 2HCl 2M

What does this mean?

Molar Mass(g/mol)

6.02 1023

particles/mol

MASSIN

GRAMSMOLES

NUMBEROF

PARTICLES

Molar Volume (22.4 L/mol)

LITERSOF GASAT STP

LITERSOF

SOLUTION

Molarity(mol/L)

D. Molarity CalculationsD. Molarity Calculations

D. Molarity CalculationsD. Molarity Calculations

How many moles of NaCl are required to make 0.500L of 0.25M NaCl?

0.500 L sol’n 0.25 mol NaCl

1 L sol’n

= 0.013 mol NaClL 1

mol0.25 0.25M

D. Molarity CalculationsD. Molarity Calculations

How many grams of NaCl are required to make 0.500L of 0.25M NaCl?

0.500 L sol’n 0.25 mol NaCl

1 L sol’n

= 7.3 g NaCl

58.44 g NaCl

1 mol NaCl

L 1

mol0.25 0.25M

D. Molarity CalculationsD. Molarity Calculations

Find the molarity of a 250 mL solution containing 10.0 g of NaF.

10.0 g NaF 1 mol NaF

41.99 g NaF= 0.95 M

NaF

L

molM

.25 L sol’n

2211 VMVM

E. DilutionE. Dilution

Preparation of a desired solution by adding water to a concentrate

Moles of solute remain the same

E. DilutionE. 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

F. MolalityF. Molality

solvent ofkg

solute of moles(m)molality

mass of solvent only

1 kg water = 1 L water

kg 1

mol0.25 0.25m

G. Molality CalculationsG. Molality Calculations

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

G. Molality CalculationsG. Molality Calculations

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

mol1.54 1.54m

H. Preparing SolutionsH. 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

H. Preparing SolutionsH. 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!” or AA – add acid!

Solution Preparation Mini-LabSolution Preparation Mini-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 12.0M concentrate. (don’t actually prepare this one!)