SCIENCES 7SCIENCES 7Chapitre 6: Chapitre 6:

Travailler avec les mélanges et Travailler avec les mélanges et les solutionsles solutions

Mercredi, le 28 fMercredi, le 28 féévrier 2007vrier 2007

Section 6.1 - Travailler avec les Section 6.1 - Travailler avec les mélanges et les solutionsmélanges et les solutions

4 définitions:4 définitions:

1. solution saturée1. solution saturée

2. solution non-saturée/insaturée2. solution non-saturée/insaturée

3. solubilité3. solubilité

4. solution sursaturée4. solution sursaturée

Méthodes de séparation

1. Les pinces2. Le magnétisme3. La flottation4. La sédimentation (ou

décantation)5. Le tamisage6. L’évaporation7. La filtration8. Le distillation

Définitions 6.2Définitions 6.2

• Taux de dissolutionTaux de dissolution: est la mesure de la vitesse à laquelle un soluté se dissout dans un solvant.

• AgitationAgitation: l’action d’agiter ou de secouer (mélanger) . Tu agites un mélange quand tu fais quelque chose qui le fait tourner dans son contenant.

Réponses de la révision 6.2 Réponses de la révision 6.2 - p.162- p.162

1. Que signifie le terme “taux de dissolution”?

• C’est la vitesse à laquelle un soluté se dissout dans un solvant.

2. a) Nomme trois facteurs qui peuvent changer le taux auquel un solide se dissout dans un liquide.

• L’agitation (mélanger), la température (chauffage) du solvant, la taille des cristaux

b) Nomme un facteur qui n’aurait pas d’effet sur le taux de dissolution.

4. a) Nomme 2 facteurs qui influent sur la solubilité d’un solide dans un liquide.

• La température du liquide, le montant de solvant/soluté, le solvant utilisé

6. Explique pourquoi l’eau chaude peut dissoudre plus de sucre qui l’eau froide.

• Les particules d’eau chaude bougent plus vite et sont plus éloignées les unes des autres, ce qui laisse plus d’espace pour les particules de sucre. Un plus grand nombre de particules d’eau entrent en contact avec un plus grand nombre de particules de sucre.

7. a) Énumère 10 substances qui se dissolvent dans l’eau (le solvant universel).

• oxygène, gaz carbonique, sel, sucre, l’alcool, le vinaigre, etc.

b) Énumère 10 substances qui ne se dissolvent pas dans l’eau.

• plastique, caoutchouc, verre, céramique, bois, tissu, l’huile, etc.

Science 7Science 7Chapter 6: Chapter 6:

Working with Mixtures and Working with Mixtures and SolutionsSolutions

Thursday, March 15Thursday, March 15thth 2007 2007

SEPARATING MIXTURESSEPARATING MIXTURES

• You are given a mixture containing sawdust, rocks, cotton balls and paperclips.

1) What things would you need to separate this mixture?

2) Write down the steps you would use to separate your mixture.

STEP 2: STEP 2: Make a PowerPoint presentation with these methods. Find pictures to add to your slides.

1. GO to the following websites: http://sciencepark.etacude.com/projects/separations/separation1.php

- Write down the definitions and examples for the methods:• Distillation• Evaporation• Filtration

2. GO to the following website:http://antoine.frostburg.edu/chem/senese/101/matter/separation.shtml

- Write down the definitions and examples for the methods:• Magnetism• Floatation

* CAN YOU FIND ANY OTHER WAYS TO SEPARATE MIXTURES?

Monday, March 19th Monday, March 19th 2007 2007 • TaskTask:

Using the internet, you must discover what dissolutiondissolution and the rate of dissolvingrate of dissolving mean.

1) Find the definitions and copy them down.2) Find examples.3) Add pictures to your notes.

*You may choose to do this on PowerPoint or Word.

Working with Mixtures and Solutions

• When we study how something dissolves, we are observing how fast a solute dissolves in a solvent. The speed at which something happens is often called a rate.

• Rate of dissolvingRate of dissolving: is the measure of how fast a solute dissolves in a solvent.

What factors do you think What factors do you think might affect the rate of might affect the rate of dissolving?dissolving?• The factors that affect this rate are

conditions that make the solute dissolve faster or slower.

• For example, to prepare a drink by mixing some flavour crystals with water, you would probably stir the mixture. In this case, stirring is the factor that changes the rate of dissolving.

How does agitation make How does agitation make solutes dissolve faster?solutes dissolve faster?

• Scientists often refer to stirring or shaking as agitationagitation. You agitate a mixture when you do something that makes it move around inside the container.

• To understand how agitation works, first consider how a solute mixes with a solvent without agitation.

• Without agitation, dissolving proceedsin 2 stages:• First the water particles pull sugar particles

loose.• Then the motion of the particles carries the

sugar particles away from the crystal.

• It takes a long time for the motion of the water particles to spread the sugar evenly through the solution. As a result the area near the crystals become very concentrated.

• As more and more sugar particles are mixed in, the solution near the crystal comes closer and closer to being saturated. The water particles near the crystal are using all of their attractive forces on the sugar particles that are already dissolved. They do not have enough attractive force left to pull more sugar particles away from the sugar crystals.

• Even when there is no stirring, the particles are always moving. Stirring moves water particles next to the sugar crystal. The water has a lower concentration of sugar, so the water particles can attract more sugar.

• Agitation is one way of making a solute dissolve faster.

• Are there other ways?