Concentration

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Concentration

8-4. Know how to calculate the concentration of a solute in

terms of grams per liter, molarity, parts per million and

percent composition. (CSS: 6d)


Concentration of a Solution

Concentration is a

measure of how much

solute is dissolved in a

given amount of

solution.

• High concentration –

large amounts of solute

in the solution

• Low concentration –

small amounts of solute

in the solution


Calculating the Concentration of a

Solution

Concentration can be

expressed in a variety of

ways:

• Molarity (M)

• Grams per Liter (g/L)

• % Composition

• Parts per million (ppm)

• Conversion Factors to

know:

• 1 gram H2O = 1 mL H2O

• 1 L = 1000 mL

Concentrat ion

AmountofSolutue

AmountofSolution


Molarity (M)

• Most commonly used in acid/base

chemistry

M

MolesofSolute

LitersofSolution

• Example: Calculate the molarity of

20.0 grams of NaOH in 100.0 grams

of H2O.

• Given:

20.0 g NaOH

100.0 g H2O

• Solve:

1. Convert grams NaOH to moles

NaOH

1molNaOH

20.0gNaOH 0. 500molNaOH

40gNaOH

2. Convert grams H2O to Liter H2O

1mL

1L

100.0gH2O

0. 1000 L

1gH O 1000 mL

3. Divide moles NaOH by Liters H2O

0.500 molNaOH

M 5. 00M

0.1000 L

• Answer: 5.00 M

2


Grams per Liter (g/L)

• Most commonly used to

express solubility

GramsperLiter

GramsofSolute

LitersofSolution

• Example: Calculate the grams

per liter of 20.0 grams of

NaOH in 100.0 mL of H2O.

• Given:

20.0 g NaOH

100.0 g H2O

• Solve:

1. Convert mL H2O to Liters

H2O

1L

100.0mL 0. 1000 L

1000 mL

2. Divide grams NaOH by Liters

H2O

20.0gNaOH

GramsperLi ter

200. g / L

0.1000 L

• Answer: 200. g/L


Percent Composition (%)

• The ratio of one part

solute to one hundred

parts solution

GramsofSolute

% Composition

x100

GramsofSolution

• Example: Calculate the

percent composition of

20.0 grams of NaOH in

100.0 grams of H2O.

• Given:

20.0 g NaOH

100.0 g H2O

• Solve:

1. Divide grams NaOH by

Grams H2O

20.0gNaOH

PercentCom position

x100

20.0%

NaOH

100.0gH O

2

• Answer: 20.0 % NaOH


Parts per Million (ppm)

• Used to describe the

concentration of very

dilute solutions.

• Most common unit for

reporting

environmental

pollutants

ppm

GramsofSolute 6

x10

GramsofSolution

• Example: Calculate the

parts per million of 0.020

grams of NaOH in 100.0

grams of H2O.

• Given:

20.0 g NaOH

100.0 g H2O

• Solve:

1. Divide grams NaOH by

Grams H2O

0.020

gNaOH 6

PartsPerMillion

x10

200 ppm

100.0 gH O

2

• Answer: 2000 ppm


What’s in your drinking water?

National Primary Drinking Water Standards as of 10/03

Contaminant

Parts per

Million (ppm)

Potential Health Effects from

Ingestion of Water

Arsenic 0.010

Skin damage or problems with circulatory

systems, and may have increased

risk of getting cancer

Asbestos (fibers >10

micrometers)

7 (million

fibers per

Liter)

Increased risk of developing benign

intestinal polyps

Carbon

tetrachloride

0.005

Liver problems; increased risk of cancer

Lead 0.015

Infants and children: Delays in physical

or mental development; children could

show slight deficits in attention span

and learning abilities; Adults: Kidney

problems; high blood pressure

Mercury (inorganic) 0.002

Kidney damage

Source: US EPA. Water On Tap: What You Need To Know. Modified 12/14/2004. EPA. 3/13/2008.

http://www.epa.gov/safewater/wot/pdfs/book_waterontap_full.pdf

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