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Intro and Definitions

Mr. Shields Regents Chemistry U12 L01

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We make or use solutions everyday in our lives.

So… what are some of these everyday examples?-Making coffee / hot chocolate /tea-Dissolving the flavors of spices into our foods-Putting additives into our gasoline-Adding anti-freeze to our cars cooling system-Dissolving salt or sugar in our food and drinks-Medicine dissolved in liquids to make them easier to take-Drinking liquids with dissolved Carbon dioxide-Dissolving chemicals in drinking and recreational water to make them safe-Breathing air into our lungs -Our bodies dissolving nutrients in our blood for nourishment

AND THERE ARE MANY MANY OTHER EXAMPLES AS WELL

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MixturesMixturesRecall that in the classification of matter there were 2 majorcategories. Do you remember what were they?

- Pure Substances (elements & compounds)- Mixtures

Mixtures are further divided into 2 categories. What are they?

- Heterogeneous mixtures (What’s the definition? Examples?)

- Homogeneous mixtures (What’s the definition? Example?)- Solutions (All kinds )

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SolutionsSolutionsThere are several different kinds of solutions. Can you name some?

Sterling silver (Cu/Ag)

We’re going to Discuss these 4

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SolutionsSolutionsSolutions we said are homogeneous mixtures. There are Two components that make up a solution…

-The Solute &

-The Solvent

In solutions one substance is usually considered to be “brokendown” into individual ions or molecules and dissolved intothe other.

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SolutionsSolutions

The substance being dissolved is called the SOLUTE

ex: NaCl is the solute when dissolved in water

The substance that does the dissolving (what the solute Dissolves in) is called the SOLVENT

ex: When Sugar is dissolved in water, water is the solvent

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Solvent vs SoluteSolvent vs Solute

The distinction between solute and solvent is notAlways so clear. For example consider the following…

A solution that is 5% ethanol & 95% water.

If you said water you would be correct …

But now consider what happens if I kept increasing the ethanol until the solution contained 60% ethanol and 40% water.

Which is the solvent?

Which one is the solvent?

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Some rulesSome rules1) If the solute and solvent are present in the Same Physical state then the Solvent is considered to be the onepresent in the larger amount.

Ex: Ethanol Water35% 65% water is the solvent55% 45% ethanol is the solvent

2) If the solute being dissolved in a solvent is presentin a Different Physical State from the solvent it is alwaysconsidered the solute no matter how much of each is present.

Ex: 5g or 120g of KNO3(s) in 100ml of H2O; KNO3 is always the solute

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Solution ConcentrationSolution Concentration

A SATURATED solution is one in which the solvent can no longerDissolve any additional solute.

An UNSATURATED solution is the opposite. It is one in whichMore solute can be dissolved in the solvent.

The Words UNSATURATED, SATURATED and SUPERSATURATED can be used to describe the amount of solute in the solvent.

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Unsat & Saturated solutionsUnsat & Saturated solutions

Sol’n can dissolve more soluteSol’n can’t dissolve anyMore solute

Solubility of Sucrose in 100mlOf water at 20º C

If I add 50 g to a sat. Sol’nIt just sits at the bottom

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SupersaturatedSupersaturated

Besides saturated and unsaturated there are alsoSUPERSATURATED SOLUTIONS

A supersaturated solution is a solution that contains MORESOLUTE in solution than the SOLVENT can normally dissolveAt a given temperature.

So how do we put more solute into solution than the solventCan dissolve???

In other words how is a supersaturated solution formed?

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Making a supersaturated Making a supersaturated sol’nsol’n

1. The solute is dissolved at some high temperature

2. The sol’n is then very slowly cooled

3. As the sol’n cools it has more solute in it than it can normally dissolve at that temperature

- Decreasing temperature decreases solubility

4. The solute concentration does not decrease so we end up with an unstable situation

5. If a single crystal is added to the supersaturated solution…

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SupersaturatedSupersaturatedThe addition of a small crystal will cause excess solute to crystallize out of a supersaturated solution immediately!

The solution remaining behind is SATURATED!

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Liquid Sol’n termsLiquid Sol’n termsTwo other terms used when both solute and solvent are Liquids –

Miscible and Immiscible

A liquid is MISCIBLE in another liquid if it is… SOLUABLE in one another IN ALL PROPORTIONS

Example: Alcohol in Water

A liquid is IMMISCIBLE in another liquid if it is… NOT SOLUBLE in one another IN ANY PROPORTION

Example: Oil in Water

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Liquid SolubilityLiquid SolubilityThe general rule of thumb is the following:

“LIKE DISSOLVES LIKE”

So What does this mean in terms of solubility?

1- Polar liquids will dissolve polar liquids

2- Non-polar liquids will dissolve Non-polar liquids

3- But Polar and non-polar liquids tend to be immiscible

Remember Polar and non-polar?

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Measuring ConcentrationMeasuring ConcentrationAll the terms we’ve used so far to discuss solution concentrationsAre subjective terms.

We’ll next discuss ways to specify solution concentrations in More objective terms

The methods we’ll look at for specifying the concentration of solutions are:

1- Molarity (M) – most common method

2- Percent (%)- mass/mass & volume/volume

3- Parts per Million (ppm) – Used for very dilute solutions