Unit 3: Matter & Mixtures

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Unit 3: Matter & Mixtures

Slide Show #5:

Concentration & Solubility

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Solubility Terms (Review)Section 8.1, p.254-258

• In slide show #4, we learned the following terms:– Solution

• Solute

• Solvent

• Dissolving

• Soluble

– Mechanical mixture• Insoluble

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Solubility Terms (Review)Section 8.1, p.254-258

• In the space below, use ALL the terms on the previous slide in a paragraph to show their meaning.

• Share your paragraph with the class or partner.

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To Dissolve or Not to DissolveSection 8.1, p.254-258 (Review)

• Why does salt dissolve in water while pepper does not?– From slide show #4, we learned that salt particles are

attracted to the water particles. This causes the salt particles to intermingle producing a solution (homogeneous mixture).

• Scientifically, when the solute particles are more attracted to the solvent particles than they are to themselves, a solution is made.

– Pepper, on the other hand, is more attracted to themselves than to the water, so they remain clumped together forming a mechanical mixture (heterogeneous).

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Review QuestionsSection 8.1, p.254-258

• Complete the following questions as review:– Page 261: #1, 2, 3, 4, & 7– These are to be done at home and will be

checked!

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ConcentrationSection 8.2, p.262-263

• Read pages 262 and 263.

• What is a concentrated solution?– A concentrated solution is

• What is a dilute solution?– A dilute solution is

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• In the table below, given examples of solutions that would be considered concentrated or dilute:

Concentrated Dilute

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• What does the term concentration mean?

– Concentration refers to the amount of solute dissolved in a certain amount of solvent.

– Concentration can be expressed in two ways:• In words – qualitatively

• With numbers - quantitatively

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Concentration - QualitativeSection 8.2, p.262-263

• When you describe the concentration of a mixture qualitatively, you often use the words dilute or concentrated.– Ex: My glass of lemonade tastes very

strong. It is too concentrated.

– Ex: My glass of Kool-Aid tastes watery. It is too dilute.

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Concentration - QualitativeSection 8.2, p.262-263

• A key indicator for identifying and describing solutions qualitatively as dilute or concentrated is color.

• As you can see from the picture below, the higher the concentration, the darker the color.

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Concentration - QuantitativeSection 8.2, p.262-263

• When you describe the concentration of a mixture quantitatively, you must determine the concentration mathematically using numbers.– You may already be familiar with the word

quantity which means amount.– The quantitative concentration is commonly

given as g/L (grams/liter). This tells you the mass of the solute in grams for every liter of solution.

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• Examples:– A) Josh mixed 120mg of hot chocolate into

one liter of hot water.• Concentration = 120 mg/L

– B) Alexis mixed 30 g of salt in 2 liters of water.

• Concentration = 30g/2L = 15 g/L• What was done mathematically here?

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• Sometimes it is necessary to set up equivalent fractions before you can determine the concentration.

• Example: Mrs. Stewart put 10g of sugar in her cup of coffee (250 mL). What is the concentration?

– In this case, it is easier to convert liters to milliliters: 1L = 1000mL. 1 0

2 5 0 1 0 0 01 0 4

2 5 0 4

4 0

1 0 0 04 0 1 0 0 0

4 0

g

m L

x

m Lg

m L

g

m Lx g m L

x g L

/

/

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• Example 2: Ms. Stanley added 15g of coffee to 500 mL of water. What is the concentration?– We’ll do this one together on the board:

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• You try these!– Hilary added 24 mg of Kool-Aid to 2 liters of

water.

– Matthew mixed 12 g of salt in 3000 mL of water.

– Katie added 15 mg of sugar to 2 cups of tea.(1cup = 250mL)

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A Limit to ConcentrationSection 8.2, p.264

• Read “A Limit to Concentration” on p.264.• You all have most likely experienced a

time when you could not dissolve all the Kool-Aid or hot chocolate that you added to your water or milk!– When a solution can no longer dissolve any

more solute, it is said to be saturated. Until this point is reached, the solution is unsaturated.

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A Limit to ConcentrationSection 8.2, p.264

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SolubilitySection 8.2, p.264

• Read “Solubility” on p.264.• We have already learned that a salt is soluble in

water since it dissolves.• Solubility refers to the amount of solute (salt)

that can dissolve in a certain amount of solvent (water) at a given temperature.– Your text says that the solubility of salt in water at 0oC

is 357 g/L. This means that for every liter of water, 357 g of salt can dissolve.

– What would happen if you tried to dissolve 400 g of salt?

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SolubilitySection 8.2, p.264

• The following solutes were mixed into a liter of water at 0oC. Using the table given on page 264, classify the solutions as saturated or unsaturated.

Solute Saturated Unsaturated

60g of

Baking soda

5g of CO2

100g of ethanol

1792g of sugar

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Rate of DissolvingSection 8.2, p.265-266

• Read pages 265-266.• Rate of dissolving refers to how fast

something will dissolve. • Your text discusses 2 factors that

effect rate of dissolving:1. Stirring2. Size of solute

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1. Stirring• When you stir a mixture, you cause the solute

particles to interact with the solvent particles more quickly.

• As a result, the rate of dissolving increases.• Check out this animation!

• Stirring, however, does NOT affect the solubility of a substance.

• You can try to stir pepper in water as long as you want, but you will not be successful!

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2. Size of Solute (p.266)• When you put a sugar cube into a glass of water,

the outside of the sugar cube dissolves first.• Breaking up the sugar cube exposes more of the

sugar (see Fig.8.12, p.266). • Since there is more interaction between the sugar

particles and the water particles, it dissolves faster. That is, the rate of dissolving increases.

• Does the size affect the solubility?

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Factors of SolubilitySection 8.2, p.267-271

• Read pages 267-271.• Both stirring and the size of the solute do NOT

effect the solubility of a substance. – That is, the amount of solute that dissolves will not

change when these factors change. Only the speed of dissolving changes.

• Your text, however, discusses 2 factors that do effect the solubility:

1. Pressure2. Temperature

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1. Pressure (p.267)

• When liquids are under pressure, more gas can dissolve in the liquid.

– This is because the pressure forces the gas particles in the spaces between the liquid particles.

– When this pressure is released, the gas comes out of the solution. This explains the “fizz” from a pop when it opens or a diver getting “the bends” if they rise too quickly from a large depth.

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• Temperature

• The temperature of the solvent has a great impact on the solubility of a solute. We will now complete a lab to determine this relationship!

• Lab 8-2A: “How Does Temperature Affect Solubility?”, p.268 – 269.

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Chapter 8 Reviewp.274-275

• Assignment:– #2,3,5,6,7,9,10,11,12, p.274-275

Documents

Unit 3: Matter & Mixtures