Solutions Unit 6 1 Solutions Homogenous Mixture (Solution) two or - - PowerPoint PPT Presentation

Solutions

Unit 6

1

Solutions

Homogenous Mixture (Solution) – two or more substances mixed together to have a uniform composition, its components are not distinguishable from one another

Heterogenous Mixture (Not a Solution) Homogenous Mixture (A Solution) Ice Water (w/ Ice Cubes) Smog Oil and Water Sea Water Air Gasoline (a mixture of hydrocarbons)

2

Solution Terminology

Solvent – the dissolving medium (usually present in the greatest amount) . . . for

• ur purposes is generally water

Solute – the substance dissolved in the solvent

+ = http://www.docbrown.info/page03/3_52states.htm

3

Solution Formation

• 1. Solvent molecules

surrounds solute molecules and “attach” to them.

http://www.elmhurst.edu/~chm/vchembook/171solublesalts.html

http://www.northland.cc.mn.us/biology/Biology111 1/animations/dissolve.html

Move of Dissolution:

4

Solution Formation

• 2. Attraction between

solvent /solute particles is greater than those between the solute particles. Solute particles get pulled apart.

http://www.elmhurst.edu/~chm/vchembook/171solublesalts.html

Movie of Dissolution w/ Narration:

http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/molvie1.swf 5

Solubility

The maximum amount of solute a given amount of solute can dissolve is called the solubility. Solubility is often referred to in units of grams of solute per 100 mL of solvent. A solution containing the maximum amount

• f solute is saturated.

Unsaturated means the solution can hold more solute.

6

Factors Affecting Solubility

Factors Affecting Solubility:

• Type of solute and solvent.
• Temperature of liquid solvent

– Solids and liquids generally increase solubility with temp. – Gases generally decrease solubility with temp.

• Atmpospheric pressure increases solubility
• f gases

7

Solubility Graphs

1. Which solute is most/least soluble at 25

• C? At 100 oC?

2. Is it possible to dissolve 100 g of sodium nitrate in 100 mL of water at 30

• C? (How much, if any,

will not dissolve?) Solid solute that will not dissolve is called a precipitate.

8

Concentration of Solutions I

Concentrated Solutions – lots of solute per given amount of solvent Dilute Solutions – little solute per given amount of solvent

9

Concentrations of Solutions II

Molarity (M) – a way to express concentration numerically

Solution

• f

Liters Solute

• f

Moles (M) Molarity 

Steps to make a solution:

• 1. Mass the correct number of moles of

solute.

• 2. Add solid to volumetric flask of correct

volume.

• 3. Add part of solvent, dissolve solute,

add the rest of solution.

Volumetric Flask

10

Molarity Calculations

e.g.

What is the molarity of 30.0 g of NaOH (M. Wt. = 40.0 g/mol) dissolved in 0.500 L of solution?

Solution

• f

Liters Solute

• f

Moles (M) Molarity 

NaOH mol 0.750 NaOH g 40.0 NaOH mol 1 x 1 NaOH g 30.0 

Ans:

M 1.50 L 0.500 NaOH mol 0.750 

11

More Molarity Calculations

e.g. How would you make 250 mL of a 0.50 M CaCl2 solution? (M. Wt. = 111 g/mol)

http://www.mhhe.com/physsci/chemistry/animations/chang_7e_esp/crm3s1_2.swf

• 1. Find mass of CaCl2 needed:

2

CaCl g 14 mol 1 g 111 x 1L mol 0.50 x 1 L 0.250 

• 2. Add 14 g CaCl2 to 250 mL Flask
• 3. Add ½ the water, dissolve the

solid, then add enough water to equal 250 mL of solution. For movies of solution preparation:

12

Mole Highway Calculations with Solutions

Finally, the last leg of the mole highway!

Solution Volume A (L) Moles A Moles B Solution Volume B (L)

L 1 A moles x 1 A Solution L A moles B moles x 1 A moles B moles B Solution L x 1 B moles

X Molarity A X Mole Ratio (Balanced Rxn) X 1 / Molarity B

13

Mole Highway Calculations with Solutions

Use the reaction below to find how many grams of Mg it would take to react with 10.0 mL of 6.0 M HCl?

Mg (s) + 2 HCl (aq) → H2 (g) + MgCl2 (aq)

Mg mole 1 Mg g 24 x 1 HCl L 0.010 1L molesHCl 6.0 x HCl moles 2 Mg mole 1 x

• Ans. = 0.72 g Mg

14

Mole Highway Calculations with Solutions II

Use the reaction below to find the concentration of NaOH if it takes 25.0 mL NaOH to completely react with 30.0 mL

• f 0.750 M H2SO4.

2 NaOH + H2SO4 → 2 H2O + Na2SO4

NaOH L 0.0250 1 x 1 SO H L 0.0300

4 2 4 2 4 2

SO H L 1 SO H mol 0.750 x

4 2SO

H mol 1 NaOH mol 2 x

• Ans. = 1.80 L NaOH

15

Electron/Proton Model of Atoms

(Review of Ion Formation)

• 1. Atoms contain (+) charged protons and (-)

charged electrons. . . The symbol for an electron is e -1.

• 2. Neutral atoms contain equal #s of protons and

electrons.

• 3. Atoms can lose electrons to become (+)

charged ions (cations).

• 4. Atoms can gain electrons to become (-)

charged ions (anions).

16

Electron/Proton Model of Atoms

Cation Formation Na+1 from Na

Na → Na +1 + e -1 Na Loses an electron to become Na +1

Anion Formation O -2 from O

O + 2 e -1 → O -2 O gains two electrons to become O -2

Na + 11

• 11

Na +1 + 11

• 10

+ e -1 O + 8

• 8

O 2- + 8

• 10

+ 2 e -1

17

Electric Properties of Solutions

Soluble ionic solids dissolve in water to form solutions that conduct electricity. . . These are called electrolytic solutions. Ionic solids form mobile ions in solution that can conduct electric current. Molecular substances do not dissolve in water to conduct electricity because they do not form ions.

18

Ionic Vs. Molecular Solids

Remember that ionic substances often contain metal cations and nonmetallic anions. Molecular substances are mostly made of nonmetals. Consult your ion sheet to help you identify ions.

Decide which substances below are ionic or molecular: a) KNO3 b) CO2 c) CuSO4 d) H2O

a) ionic b) molecular c) ionic d) molecular

19

The Dissolution Process

Soluble ionic substances dissolve in water to give aqueous ions: e.g.

Al2(SO4)3 (s) BaBr2 (s) NaCl (s)

http://www.chem.iastate.edu/group/Greenbowe/sections/projectfolder/flashfiles/thermochem/solutionSalt.html

→ Na +1 (aq) + Cl -1 (aq) → Ba +2 (aq) + 2 Br -1 (aq) → 2 Al +3 (aq) + 3 SO4

• 2 (aq)

20

Precipitation Reactions

Sometimes when two solutions are mixed, a solid (precipitate) is formed. The precipitate is an ionic substance that is insoluble in water. e.g.

NaCl (aq) + AgNO3 (aq) → NaNO3 (aq) + AgCl (s)

Silver Chloride is a precipitate. It forms a solid and sinks to the bottom of the test tube or beaker.

21

Ionic and Net Ionic Equations I

Ionic equations represent soluble compounds as ions and insoluble compounds as molecules. Net Ionic equations cancel out spectator ions.

Molecular: NaCl (aq) + AgNO3 (aq) → NaNO3 (aq) + AgCl (s) Ionic:

Na+1 (aq) + Cl-1 (aq) + Ag+1 (aq) + NO3

• 1 (aq) → Na+1 (aq) + NO3
• 1 (aq) + AgCl (s)

Net Ionic:

Na+1 (aq) + Cl-1 (aq) + Ag+1 (aq) + NO3

• 1 (aq) → Na+1 (aq) + NO3
• 1 (aq) + AgCl (s)

22

Ionic and Net Ionic Equations II

Write the following molecular equation into ionic and net ionic equations:

Pb(CH3COO)2 (aq) + 2 NaOH (aq) → Pb(OH)2 (s) + 2 NaCH3COO (aq) Ionic: (all ions aqueous) Pb2+ + 2 CH3COO-1 + 2 Na+1 + 2 OH-1 → Pb(OH)2 (s) + 2 Na+1 + 2 CH3COO-1 Net Ionic: (all ions aqueous) Pb2+ + 2 CH3COO-1 + 2 Na+1 + 2 OH-1 → Pb(OH)2 (s) + 2 Na+1 + 2 CH3COO-1

23

Solubility of Ionic Compounds

A table of solubilities can be used to predict which ionic compounds will not be soluble in water . . . i.e. which compounds will form precipitates. To use the table, identify the anion and cation and check to see if the combination is soluble or insoluble.

24

Solubilities

Use the table of solubilities to find if the following are soluble:

a) Na2CO3 b) PbSO3 c) AgCH3COO d) Ba(OH)2

a) Soluble b) Insoluble c) Insoluble d) Soluble

25

Colligative Properties

Adding solutes to solvents affects the properties of solvents as follows:

Property Effect Vapor Pressure Decreases Boiling Temp Increases Freezing Temp Decreases

26

Vapor Pressure

Non volatile solutes lower the vapor pressure, because they occupy reduce the number of solvent molecules on the surface of the solution and sometimes have attractions for solvent molecules.

http://www.chem.purdue.edu/gchelp/solutions/colligv.html

27

Boiling Temperature

Solutes lower the vapor pressure of solvents, thus raising the boiling temperature.

28

Freezing Temperature

Solutes interfere with solvent molecules aligning together to form solids. The freezing temperature decreases.

29