II. Concentration

(p. 203)Ch. 5 - Solutions

A. ConcentrationThe amount of solute in a solution.

Describing Concentration% by mass - medicated creams% by volume - rubbing alcoholppm, ppb - water contaminantsmolarity - used by chemists

CONCENTRATION – compares the quantity of solute to the quantity of solvent

A dilute solution has a relatively small quantity of solute per unit volume of solution. A concentrated solution has a relatively large quantity of solute per unit volume of solution.

1. % by volume

= volume of solute x100% volume of solution

Example problem: 10mL of fresh orange juice are mixed with 100mL of water. What is the % by volume of orange juice?(9.1%)

3 Ways of expressing Concentration

2.ppm: This is only used for very small amounts of solute.

= mass of solute x 10⁶Mass of solution

Example problem: 400g of water has 5.6 x10-3g of lead. What is the concentration in ppm?(14ppm)

3Amount Concentration: Used mostly in Chemistry

= Moles of solute Volume in L.

Example problem: 12g of NaCl are dissolved in 12.3mL of water. What is the molarity of the solution? (17M)

Amount Concentration (Molarity)

)O2(H solvent of L

solute of moles(M)molarity

volume of solvent onlyL 1

mol0.25 0.25M

Amount Concentration (Molarity)

Find the molarity of a solution containing 75 g of MgCl2 in 250 mL of water.

L

molM

1 mol MgCl2

95.21 g MgCl2 0.250 L

75 g MgCl2

= 3.2M MgCl2

Amount Concentration (Molarity)

How many grams of NaCl are required to make a 1.54M solution using 0.500 L of water?

L

molM

0.500 L

L

1.54 mol NaCl

= 45.0 g NaCl

58.44 g NaCl

1 mol NaCl

Listing Entities

8. List the chemical formulas for the major entities present inwater for each of the following: (a) Zinc(b) potassium dichromate(c) sodium bromide (d) acetic acid(e) oxygen (f) Sulfur(g) nitric acid (h) copper(II) sulfate(i) calcium phosphate (j) silver chloride(k) methanol (l) paraffin wax, C25H52(s)

(m) aluminum sulfate

Summary

Write dissociation or ionization equations for the following

1. sodium hydroxide2. magnesium sulfate3. sulfuric acid4. carbonic acid5. copper(II) carbonate

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Ion ConcentrationWhat is the concentration of Calcium and

Chloride ions in a 0.30mol/L solution of CaCl2

CaCl2(aq) → Ca+2(aq) + 2 Cl-1(aq)

What are the ion concentrations of the following?

1. 0.125 M sodium hydroxide2. 0.500 M ammonium

phosphate3. 1.35 M sulfuric acid4. 0.0150 M perchloric acid5. 0.246M dihydrogen phosphate

ion concentration in a sodium dihydrogen phosphate solution. L

molM

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Practice ProblemsPage 212 # 17-19

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DilutionAdding solvent (solute is unchanged) to

decrease the concentration of a solution

Dilution Formula: C1 x V1 = C2x V2

C = Concentration, V = Volume (Liters)

Example problemWater is added to 0.200L of 2.4 mol/L

cleaning solution until the final volume is 1.00L. What is the new concentration?

Dilution worksheet and p216/218 # 1,2,6,7

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Figure 14.7: Preparation of a standard aqueous solution

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Figure 14.8: Acetic acid dilution

END

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HWK Quiz Concentration1. Calculate the number of moles of HCl in

260mL of 0.24M solution.2. Calculate the concentration of a solution

with 6.2moles of HCl in 45mL of solution.

3. Calculate the volume if you have 0.12moles of 3.2M HCl

4. Calculate the g of potassium nitrate in 23mL of 6.2M solution

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HWK Quiz1. What is the concentration of a solution if

10.6g of Potassium carbonate are dissolved in 45mL of water? (2 marks)

2. 3.5L of 6.2M HCl are evaporated to give 56mL. What is the new concentration of HCl? (2 marks)

3. 2L of water is added to 6L of 0.2M HCl. What is the new concentration? (2 marks)

4. The technician has 36M HCl which is way too strong for Ms Portman’s class. They need 50mL of 2M HCl for their lab. What should he do???? (2marks)