1C. Solubility

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Objectives

1) Define the following words: solute, solvent and solution.

2) Learn why water is a good solvent.

3) Define the terms: insoluble, unsaturated, saturated and supersaturated.

4) Interpret solubility curves.5) Learn about concentration vs.

temperature and solubility.6) Learn about polarity and ionic

compounds

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1C.1: SOLUBILITY OF SOLIDS IN WATER

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What is solubility?

• Imagine dissolving a spoonful of salt in water

• How much will dissolve?

• What is the solute?• What is the solvent?

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What is solubility?

• The salt is the ____________• The water is the ______________• The mixture of the salt & the water is a

__________________• As you stir, the white crystals dissolve in the

water• The solution is colorless & clear

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What is solubility?The salt is the: soluteThe water is the: solventThe mixture of the salt & the

water is a: solution

As you stir, the white crystals dissolve in the water

The solution is colorless & clear

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Solutions - ReviewSolutions - ReviewHomogeneous mixture – uniform

or evenly distributedAll solutions are homogeneous

mixturesA solute dissolves in a solvent to

make a solutionSolutions are clear but not

necessarily colorless

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Do Now

Define the following words:

Solute

Solvent

Solution

Provide an example of each

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What is solubility?

• What would happen if you added another spoonful of salt?

• And another…. And another?• Eventually, you wouldn’t be able to dissolve

any more. Some salt would fall to the bottom, no matter how long you stirred.

• The solution would be saturated; it would hold all the solute it could.

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No more salt can dissolve.The solution is saturated.

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What is solubility?

• If you heated the water, you might be able to dissolve a little more salt.

• The maximum quantity of a substance that can dissolve in a certain quantity of water – at a specified temperature – is called its solubility.

• You might say grams of salt per 100 grams of water at 20oC

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What is solubility?• Although size of the salt crystals & how

vigorously you stir affect how long it would take for the salt to dissolve, they do not affect how much can dissolve at a specified temperature

• The amount of solute that can dissolve is affected by temperature.

• Usually, the higher the temperature the more solute that can be dissolved.

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Temperature & SolubilityThe amount of solute

that can dissolve in a specified amount of solvent varies with temperature

The graphical representation of this relationship is called the solute’s solubility curve: page 54

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Temperature & Solubility

Each point on the solubility curve indicates a solution in which the solvent contains as much dissolved solute as it normally can at that temperature

Such a solution is called a saturated solution

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Temperature & Solubility

• Question: At 40oC, how much KNO3 will dissolve in 100 g water to form a saturated solution?

• Answer:

15

Temperature & Solubility

Question: At 40oC, how much KNO3 will dissolve in 100 g water to form a saturated solution?

Answer: 60 grams

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Temperature & Solubility

• Question: At 90oC, how much KCl will dissolve in 100 g water to form a saturated solution?

• Answer:

17

Temperature & Solubility

Question: At 90oC, how much KCl will dissolve in 100 g water to form a saturated solution?

Answer: 52 grams

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Temperature & SolubilityQuestion: At

50oC, how much KNO3 will dissolve in 100 g water to form a saturated solution?

Answer:

19

Temperature & SolubilityQuestion: At

50oC, how much KNO3 will dissolve in 100 g water to form a saturated solution?

Answer: 80 grams

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Temperature & Solubility

• Question: At what temperature will 70 g of KNO3 dissolve in 100 g of water to make a saturated solution?

• Answer:

21

Temperature & Solubility

Question: At what temperature will 70 g of KNO3 dissolve in 100 g of water to make a saturated solution?

Answer: 45oC

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Temperature & Solubility

• Question: Which one of the three solutes is the most affected by temperature?

• Answer:

• Question: The least affected?

• Answer:

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An unsaturated solution is a solution that

contains less dissolved solute than the

amount that the solvent can normally hold at that temperature.

On a solubility curve this is area below the line.

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Unsaturated solution

Temperature & Solubility• Think about a

solution that contains 80 g of KNO3 in 100 g of water at 60 oC

• The point is below the curve

• This is an unsaturated solution

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Classwork

Review sample problems on page 55 and 56.

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Temperature & Solubility

• What do you expect would happen if you cooled a saturated solution?

• Crystals would form and fall to the bottom – usually

• Sometimes, cooling a saturated solution does not cause crystals to fall out

• This is an unstable solution called a supersaturated solution

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A supersaturated solution is a solution that contains more dissolved solute than the amount that the solvent can normally hold at that temperature.

This normally occurs if you cool a saturated solution.

This new point lies above the solubility curve.

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Supersaturated solution

Rock CandyWhen seed crystals are added to a supersaturated sugar solution, they cause excess dissolved sugar to crystallize onto a string

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Hot SpringsAs the water in Emerald Pool (Yellowstone National Park) cools and evaporates at the edges, it becomes supersaturated, and precipitates begin to form.

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1C.2 : SOLUBILITY & SOLUBILITY CURVES

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Solubility curves are quite useful when working with 100 grams of water.

But what happens when you work with other quantities of water.

A mathematical expression sing proportions can be used.

Question• How much potassium nitrate will dissolve

in 150g of water at 40°C? refer to chart: At 100 grams water 60 grams

will dissolve at 40°C• Answer:

The quantity of solvent has increased from 100 grams to 150 grams – 1.5 times as much solvent. That means 1.5 times as much solute can be dissolved.

Thus 1.5 x 60 grams KNO3 = 90 grams KNO3

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Another way to solve:

60 g KNO3 = x g KNO3

100 g H2O 150 g H2O

(150 g)(60 g) = (100 g)(X)

X = 90 g

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Classwork

Page 56Questions 1-3

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Homework

Solubility Worksheet

Due: Wednesday, Nov 13th

1C.3: Constructing a Solubility Curve

Lab

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Lab: Constructing a solubility curve

Investigating Matter, pp. 57-59

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Do Now

• Explain why the crystals formed in the experiment yesterday.

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1C.4: DISSOLVING IONIC COMPOUNDS

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IONIC COMPOUNDS

Formed from a cation (+) and an anion (-)

Example: Na+ Cl- NaCl

Dissolving Process

• When you dissolve Potassium Nitrate (KNO3), an ionic compound, in water in a lab experiment this is referred to as a:

• macroscopic phenomenon (observable)• Chemistry is concerned with what happens at

the particulate level – atomic and molecular phenomenon, which cannot be observed easily.

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Dissolving Process• Factors that contribute to dissolving a solid

material (macroscopic ):– Temperature– Agitation– Time

• But how do the particles of solute & solvent interact to make dissolving happen?

• This occurs at the microscopic level.

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Water’s Role

• Water is a polar molecule• Although it is neutral

overall, it has an uneven distribution of electrical charge.

• Partial positive region at one end (hydrogen side).

• Partial negative region at other end (oxygen side).

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Polar Molecule – A molecule which has an uneven distribution of electrical charge.

One half of the molecule is more positive (+) and the other half is more negative (-).

Water’s Role

• It has a bent or V-shape• The Oxygen end has

greater concentration of electrons (-) than the two Hydrogen ends (+)

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Water’s Role

Polar water molecules are attracted to other polar substances & to substances composed of electrically charged particles

Electrical attractions make it possible for water to dissolve many kinds of substances

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Salt Dissolving in WaterThink about the ions & molecules interacting at different times.

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Salt Dissolving in Water

• Q. What forces hold the ionic lattice together?

• A. Opposing ionic charges (+ and – charges). An electrical attraction.

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Salt Dissolving in Water

• Q. Why do the water molecules interact with ions?

• A. Water’s molecular polarity allows it to interact with both positive & negative ions.

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Salt Dissolving in Water

• Q. What do the dissolved ions have in common with each other?

• A. They are all solvated – surrounded – by water molecules.

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Salt Dissolving in Water

• Q. How are the dissolved ions different?

• A. Positive H ends of H2O are aligned with negative Cl ions, and negative O ends of H2O are aligned with positive Na ions

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Salt Dissolving in Water

Q. On the particulate level, what would evaporating water imply for this system?

A. The crystal lattice would begin to reform with fewer water molecules to overcome the ion-ion attractive forces.

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Water’s RoleView “Modeling Matter: Attraction Between

Particles”Q. What factors influence whether or not an

ionic compound dissolves in water?A. Properties of both solute & solvent, because

dissolving involves competition among 3 types of attractions:◦Solvent – Solute◦Solvent – Solvent ◦Solute – Solute

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Water Video

• Go to:• http://www.sumanasinc.com/webconten

t/animations/content/propertiesofwater/water.html

• Show video

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Do Now

• Draw a calcium ion solvated by water molecules.

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Do Now

• What is meant by unsaturated and supersaturated?

• How does water interact with ionic compounds?

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1C.6: SOLUTION CONCENTRATION

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Objectives

• 1. Define solute concentration.

• 2. Explain the relevance to environmental chemists

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The terms saturated and unsaturated are not always adequate to describe the properties of solutions.

Solution concentration refers to how much solute is dissolved in a specific quantity of solution.

Ways to express solution concentration:1) water-solubility curves2) percent values (parts of solute per hundred parts solution (pph)

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Example

Dissolving 5 grams of table salt in 95 grams of water produces 100 grams of solution

solute + solvent = solution

The percent solution of table salt is 5%

grams solute / grams solution x 100 = % solution

5 grams / 100 grams x 100 = 5%

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Why is solution concentration important?

It is used in your daily lives. For example, preparing beverages from premixed concentrate, adding antifreeze to water in automobile radiators and mixing pesticide or fertilizer solutions all require use of solution concentration.

Other uses:Determining percentage of heavy metal pollutants (lead and mercury) in water.

1C.7: DESCRIBING SOLUTION CONCENTRATIONS

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Sample Problem 1

A common intravenous saline solution used in medical practice contains 4.5 grams NaCl dissolved in 495.5 grams distilled water.

What is the concentration of this solution expressed as a percentage?

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Solute – 4.5 grams NaCl

Solvent – 495.5 grams distilled water

Solution total – 500 grams

grams solute / grams solution x 100 = % solution

4.5 grams / 500 grams x 100 = 0.90%

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Sample Problem 2

One teaspoon of sugar, with a mass of 10.0 grams is dissolved onto 240.0 grams of water.

What is the concentration of this solution expressed as a percentage?

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Solute – 10.0 grams sugar

Solvent – 240.0 grams water

Solution total – 250 grams

grams solute / grams solution x 100 = % solution

10 grams / 250 grams x 100 = 4%

Classwork

Worksheet Unit 1C Section 6

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Homework

Worksheet

Solution concentration problems

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1C.8: INAPPROPRIATE HEAVY-METAL ION CONCENTRATIONS?

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Objectives (1C.8 AND IC.9)

• 1. Define heavy metals, green chemistry, regulatory limits, acids, bases, alkaline, and pH.

• 2. Describe the health concerns for Pb2+ and Hg2+.

• 3. Describe the pH ranges that affect the health of fish

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Heavy Metals• Many metal ions are essential to our health

– Iron(II) Fe2+

– Potassium K1+

– Calcium Ca2+

• Some “heavy-metal” ions are harmful.– Masses are heavier than the essential metal

ions.– Toxic: bind to proteins, preventing them from

performing their normal tasks– Nervous system, brain, kidneys, liver, death– Lead Pb2+

– Mercury Hg2+

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Heavy Metals

• Not removed as waste as they move through the food chain

• Concentrated in bodies of fish & shellfish – even when present in low concentrations in surrounding water

• Hard to detect in low concentrations• Difficult & costly to remove• How to prevent poisoning?• Prevention: “Green Chemistry” (replace

harmful chemicals)75

Lead Ions (Pb2+)• Plumbum – Plumber – ancient Roman water pipes• Pottery, automobile batteries, solder, cooking

vessels, pesticides, paints (primary ingredient in red paint that protects bridges & other steel structures from corrosion), candy wrappers.

• Leaded gasoline – phased out in the 1970s – was a better burning fuel. Soils around heavily traveled roads are still contaminated (tetraethyl lead)

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Mercury Ions (Hg 2+)• Only metallic element

that is a liquid at room temperature

• Hydragyrum – liquid silver or quicksilver

• “silent” light switches, street lamps, thermometers, thermostats, fluorescent light bulbs, paints, antiseptics, fungicides, pesticides

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During the 18th & 19th centuries, mercury

compounds were used in the making of felt

hats.

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Ultimately, mercury poisoning caused symptoms such as

numbness, staggered walk, tunnel vision, and brain damage, giving rise to the

expression “mad as a hatter.”

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Heavy Metals• A sudden release of a large amount of a

heavy-metal ion might cause a fish kill

• It would depend on:– what ion – its concentration– species of fish– other factors

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1C.9: INAPPROPRIATE pH LEVELS?

SKIP

ACID/BASE POWERPOINT

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1C.9: pH LAB

HANDOUT

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8383

SKIP

pH• pH scale reports: acid, bases, or chemically neutral• pH usually between 0 to 14

< 7 - acid (lower numbers, more acidic)= 7 - neutral> 7 - base/alkaline (higher numbers, more

basic)• Change in 1 pH unit = 10X difference

• Ex. Soft drinks = pH of 3• Lemon juice = pH of 2• Lemon juice is 10X more acidic than soft

drinks

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pH Scale

• Draw the pH scale and label the following on it– Weak acid– Strong Base– Strong Acid– Neutral– Weak Base

0 1 3 5 7 9 11 13 14

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What comes to mind when you hear the word acid?

Do you think of a substance that will burn your skin or burn a hole in your clothes?

Do you think about sour foods?

All acids have some properties in common

Acids

Characteristics of AcidsACIDS• Form H+ in water

– HCl, H2SO4, H3PO4

• Litmus: blue to red

• Sour – Don’t taste!

• Conduct electricity

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You don’t consume many foods with bases.

Some foods like eggs whites are slightly basic.

Some bases are used in medicines.

Bases are commonly used in soaps and household cleaners.

Bases

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Characteristics of BasesSome contain OH- ions : • sodium hydroxide (NaOH) – drain and oven

cleaners • calcium hydroxide (Ca(OH)2) – used in cement

Other bases do not contain OH- ions•ammonia (NH3) – household cleaners •Baking soda (NaHCO3)

• Litmus: red to blue• Bitter – Don’t taste!• Conduct electricity

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pH of Common Substances

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Do Now

• Where are acids located on the pH scale?

• Where are bases located on the pH scale?

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pH continued

• Neutral solutions (pH = 7) are neither acids nor bases– NaCl (table salt) is an ionic compound that is

neutral– C12H22O12 (sugar) is a molecular compound that is

neutral• Rainwater is slightly acidic (pH ≈ 5.8)• Both acids & bases effect living things• EPA requires drinking water be between 6.5

to 8.5

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pH continued

• Too low a pH in rivers, lakes, & streams– Impairs fish egg development – affects

reproduction– Increases concentration of metal ions –

by leaching metal ions from surrounding soil – Al3+ can be toxic to fish in high concentrations

• Too high a pH– Can dissolve skin & scales

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pH continued

• EPA requires pH of drinking water be between 6.5 to 8.5

• Fish can tolerate a pH between 5.0 to 9.0

• Expert anglers try to fish in water with a pH between 6.5 and 8.2

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pH balance in swimming pools is possibly the most critical element of pool water maintenance. If you consider that chlorine's ability to do its job is directly linked to the pH, high or low levels inevitably lead to sanitization problems.

The ideal range for pH in swimming pool water is 7.0 - 7.6 . The pH of our eyes is typically 7.2 - 7.4 .

If the pH is kept at the same level as that in our eyes, the side-effects of burning red eyes is kept to a minimum. The ability of chlorine to disinfect at this level is also optimum.

pH balance in swimming pools

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High pH in swimming pool water

High pH in swimming pool water may result in one or more of the following problems:

•scaling or calcium buildup on pool surfaces, waterline and accessories;•dull or cloudy pool water;•clogging of filter medium or elements;•drop in disinfection potential of chlorine resulting in algae growth;•burning eyes and nose;•dry, itchy skin and scalp.

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To lower the pH in pool water

Adding an acid to the pool water reduces the pH. The most common chemicals used to reduce high pool water pH are:

•muriatic acid - typically 30% - 35% liquid hydrochloric acid.•sodium bisulfate - granule or powder pH reducer, dry acid.•sulfuric acid•nitric acid - highly corrosive but is known to work well.

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Low pH in swimming pool water

Low pH in swimming pool water may cause one or more of these problems:

•eroding of the pool plaster or grouting;•corroding of the metal pool accessories (steps,

heater . . .);•staining resulting from metal corrosion;•rapid dissipation of chlorine requiring increased dosage;•burning eyes and nose;•dry and itchy skin and scalp;•perishing of swimwear, pool toys and accessories.

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To raise the pH in pool water

Adding a base raises the pH of the pool water. The active ingredient is usually sodium carbonate.

Often low pH is a result of acid rain and occurs after periods of heavy precipitation.

1C.10: MOLECULAR SUBSTANCE

SKIP

104

Objectives

1. Explain what are molecular substances.

2. Compare ionic versus molecular compounds.

3. Distinguish between polar and non polar substances.

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Molecular Substances

• Ionic substances are solids at room temperature

• Ionic substances release ions when they dissolve in water (NaCl)

• Composed of a metal and non-metal

• Molecular substances are found as solids, liquids, or gases at room temperature

• Composed of non-metals only (C, H, O)

• Molecular substances remain as whole molecules when they dissolve in water

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Molecular Substances• Molecular substances are found as solids, liquids, or

gases at room temperature – physical state depends on strength of attraction among the molecules.

• Examples:• O2 – weak attraction between oxygen atoms – gas

• Ethanol and water – slightly stronger attraction between atoms – liquids.

• Sugar – very strong attraction between atoms – solid.

Molecular Substances

• What determines the solubility of a molecular substance in water?

• Attraction of a substance’s molecules for each other compared to their attraction for water molecules

• Distribution of electric charge within the molecules is a major factor

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Molecular Substances• Most molecular compounds contain atoms of

nonmetallic elements (right side of periodic table).

• Remember, these atoms are linked together by the attraction of one atom’s positive nucleus to another atom’s negative electrons

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Molecular Substances• If the differences in attractions between the

two atoms are big enough, electrons move from one atom to another, forming ions (NaCl). A metal and non-metal.

• If the differences in attraction between the two atoms exist but are not that big, they may cause the electrons to shift around and become unevenly distributed (H2O).

• The ability of an atom to attract electrons is known as its electronegativity.

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111111

Polar Molecule – A molecule which has an uneven distribution of electrical charge.

One half of the molecule is more positive (+) and the other half is more negative (-). Oxygen is more electronegative.

Molecular Substances• “Like Dissolves Like”• Polar molecules dissolve in polar solvents• Examples: sugar in water, alcohol in water,

antifreeze in water. All are polar molecules.• Nonpolar molecules dissolve in nonpolar solvents• Examples: oil-based paint in paint thinner,• The reason to use soap and shampoo to remove dirt

and oil from skin and hair.• Nonpolar molecules (gas and oil) do not dissolve well

in polar molecules (water). This is why oil and water do not mix.

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Common Nonpolar substances

• Hexane• Lamp Oil• Paint Thinner• Fats• Motor oil• Cooking oils

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Concept ChartSolubility

Ionic compounds Molecular Substances

Polar compounds Non polar compounds

Explain how it dissolves:

Explain how it dissolves:

Explain how it dissolves:

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Homework

• Page 83• Questions: 17, 18, 19, 20, 21, 23, 24 and 25

• Due: Today

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Problem

• Explain why oil and water do not dissolve in each other.

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Problem

• Explain why oil and water do not dissolve in each other.

• Polar substances dissolve polar substances.• Polar substances dissolve ionic compounds.• Non-polar dissolves non-polar substances.

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Solubility Review

• Polar Substances dissolve other __________ or ____________.

• Non Polar Substances dissolve _______________.

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1C.12: DISSOLVING GASES INTO WATER?

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Objectives

• 1. Describe the difference between solubility of solids and gases.

• 2. Explain the metabolic changes of fish as temperature and dissolve oxygen change.

• 3. Describe factors that can change the amount of dissolved oxygen.

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Oxygen & Other Gases

• Ionic & molecular solids tend to have a higher solubility at higher temperatures.

• The opposite tends to be true for gases.

• Also, most gases are much less soluble in water than solids are – at any temperature.

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Problem• Turn to page 75 and use the chart: • What mass of O2 can be dissolved in

1000.0 g of water at 25.0 °C?

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Oxygen & Other Gases• In addition to the temperature & the type

of solvent, the solubility of a gas also depends on gas pressure.

• Is this relationship directly or inversely proportional?

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Oxygen & Other Gases• Is this relationship directly or inversely

proportional?• Solubility of gases are directly proportional

to pressure if temperature remains constant.• As pressure doubles, so

does solubility.

Example• Turn to page 76 and use the chart:

• What mass of O2 can be dissolved in 1000.0 g of water at 3 atm pressure and 25.0 °C?

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Gases• Soda has extra CO2 forced into it under

high pressure. More CO2 dissolved.

• When can is opened the pressure is reduced.

• When a can or bottle of soda is opened, the solution is now supersaturated at the lower pressure, & some excess dissolved CO2 escapes as bubbles.

• The “flat” soda is still saturated with the gas at the lower pressure.

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1.C. 13: TEMPERATURE, DISSOLVED OXYGEN, AND LIFE

SKIP

127

Objectives

• Examine what happens to fish when too much or too little oxygen dissolves in water.

• You just learned how the solubility of gases is affected by temperature.

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Temperature & Dissolved Oxygen• Does the temperature of water affect fish survival?• Dissolved-oxygen requirements for fish.• The metabolism of fish increase with water temperature.

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Temperature & Dissolved Oxygen• How does a temperature change affect fish?• Cold-blooded: body temperatures rise & fall

with the water temperature• Rise

– Increases metabolism– Eat more– Swim more– Require more dissolved oxygen– Also increases metabolism of other aquatic

organisms (i.e., aerobic bacteria) that compete with fish for dissolved oxygen

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Temperature & Dissolved Oxygen

• Rise in temperature, decreases the amount of dissolved O2 in the water while it increases the fish’s need for it

• A long stretch of hot summer days sometimes kills fish because there is not enough oxygen dissolved in the water.

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Temperature & Dissolved Oxygen

• Hot, summer days are not always the cause.

• Many industries use water to cool their heat-producing processes, dumping the heated up water back into the rivers or lakes.

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Temperature & Dissolved Oxygen

• Can too much dissolved oxygen be a problem?

• When oxygen gas dissolves, so does nitrogen which is found in the atmosphere.

• When the total amount of dissolved gas reaches between 110% to 124% of saturation (a supersaturated state), gas-bubble trauma may develop in fish

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Temperature & Dissolved Oxygen

• Gas bubbles form in the blood and tissues of fish.

• Nitrogen bubbles block the capillaries.• Death within hours or days.• Prompt dissection after death can find gas

bubbles in the gills.• Bubbling of gas in the blood in humans is

known as the “bends” and affect scuba divers.

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Supersaturation of water with oxygen & nitrogen can occur at the base of a dam or hydroelectric project, as the released water

forms “froth,” trapping large

quantities of air

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Problem

• Explain what happens to the amount of dissolved oxygen as the temperature increases?

• How about when the pressure increases?

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Homework

• Pg. 83; Questions: 28 - 31,

• Pg. 84; Questions: 33 and 35

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End of Unit

1C.11: SOLVENTS

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Investigating Matter, pp. 72-75

1C.11: SOLVENTS

LAB

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Dissolving Substances (Lab)

• List several substances that will dissolve in water and why….

• Hexane is NON POLAR, list several substances that will dissolve in hexane.

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