SCIENCES 7 Chapitre 6: Travailler avec les mélanges et les solutions Mercredi, le 28 février 2007

Section 6.1 - Travailler avec les mélanges et les solutions 4 définitions: 1. solution saturée 2. solution non-saturée/insaturée 3. solubilité 4. solution sursaturée

Méthodes de séparation Les pinces Le magnétisme La flottation La sédimentation (ou décantation) Le tamisage L’évaporation La filtration Le distillation

Définitions 6.2 Taux de dissolution: est la mesure de la vitesse à laquelle un soluté se dissout dans un solvant. Agitation: 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 - p.162 Que signifie le terme “taux de dissolution”? C’est la vitesse à laquelle un soluté se dissout dans un solvant. 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.

b) Énumère 10 substances qui ne se dissolvent pas dans l’eau. 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 7 Chapter 6: Working with Mixtures and Solutions Thursday, March 15th 2007

SEPARATING 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: Make a PowerPoint presentation with these methods STEP 2: Make a PowerPoint presentation with these methods. Find pictures to add to your slides. 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 Magnetism Floatation * CAN YOU FIND ANY OTHER WAYS TO SEPARATE MIXTURES?

Monday, March 19th 2007 Task: Using the internet, you must discover what dissolution and the rate 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 dissolving: is the measure of how fast a solute dissolves in a solvent.

What factors do you think might affect the rate of 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 solutes dissolve faster? Scientists often refer to stirring or shaking as agitation. You agitate a mixture when you do something that makes it move around inside the container.

Without agitation, dissolving proceeds in 2 stages: To understand how agitation works, first consider how a solute mixes with a solvent without agitation. Without agitation, dissolving proceeds in 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 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?