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Chapter 3: Mixtures and Their Uses Science 14 Slide 2 Introduction Recall: We have learned that most substances are mixtures rather than pure substances. Examples: Salad Dressing, Windex (pg. 43) Slide 3 Introduction What happens to water in a flood? It becomes contaminated Can cause people to become sick from drinking it Slide 4 Introduction We can classify water into several different categories: Safe water (water you can drink without getting sick) Clear water (looks safe but may contain contaminants that make you sick) Dirty water (contains silt, sewage and other debris) Slide 5 Introduction How can dirty water be turned into clear water? Letting solid particles settle to the bottom Filtering Once the dirty water is turned into clear water, it can then be treated to make it drinkable. Slide 6 Introduction Dirty water is a mechanical mixture. Clear water is a solution of water and other substances. Safe water is also a solution of water and other minerals. Slide 7 3.1 Two Kinds of Mixtures matter Pure substance mixture element compound element Mechanical mixture solution Slide 8 3.1 Two Kinds of Mixtures Mechanical Mixtures a mixture in which more than one type of particle is visible AKA: Heterogeneous Mixture Examples: Wet concrete Orange juice with pulp Sand/gravel Slide 9 3.1 Two Kinds of Mixtures Solutions A uniform mixture made of two or more substances (looks like a pure substance) AKA: homogeneous mixture Examples: Shampoo Pop Syrup Slide 10 3.1 Two Kinds of Mixtures Parts of Solutions Solute the substance that dissolves (most solutions have less solute than solvent) Solvent - the substance in which the solute dissolves Example: salt water Solute salt Solvent - water Slide 11 Practice! In each of the following solutions, identify the solute and solvent(s) Baking soda and water air( (78% nitrogen, 22% oxygen and other gases) Gold jewelry (90% gold, 10% silver) Slide 12 Answers Baking soda (solute) and water (solvent) air( (78% nitrogen [solvent], 22% oxygen and other gases [solutes]) Gold jewelry (90% gold [solvent], 10% silver [solute]) Slide 13 3.1 Two Kinds of Mixtures So whats the difference between mechanical mixtures and solutions? SolutionsMechanical Mixtures appear to contain only one substance may be transparent have parts that are not easily separated have limited solubility (proportions) appear to contain more than one substance have parts that are easily separated can be mixed in any proportion Slide 14 3.1 Two Kind of Mixtures How can we tell the difference between mechanical mixtures and solutions? Observation if we can see more than one substance then it is mechanical Using a filter if anything gets caught in the filter then it is mechanical Slide 15 Practice Questions Hand-in/Email: Solutions Practice Worksheet Check Your Understanding Questions from Pg. 44 #1-3 Slide 16 3.2 What Are Solubility and Concentration? Concentration describes the amount of solute in a solution Manufacturers include the concentration of the solution on the label of many products Can be shown in many ways: Mass per unit volume (g/L) Percent by mass (% w/w) Percent by volume (% v/v) Molarity (mol/L) Slide 17 3.2 What Are Solubility and Concentration? 1. Mass per unit volume (g/L) -most common way -Mass per unit volume is handy when discussing how soluble a material is in water or a particular solventsolvent Example: see Figure 3.5 on p. 45 Roundup solution of glyphosphate and water Label says the product contains 7.0 g/L glyphoshpate in 1 L of product Slide 18 3.2 What are Solubility and Concentration? 2. Percent by Mass. Also called weight percent or percent by weight, this is simply the mass of the solute divided by the total mass of the solution and multiplied by 100%:solution Example: For example, a solution consisting of 30 grams of sodium chloride and 70 grams of water would be 30% sodium chloride by mass: (30)/(30+70)*100 = 30% Slide 19 3.2 What are Solubility and Concentration? 3. Volume to volume percentage: most useful when a liquid - liquid solution is being prepared (although it is used for mixtures of gases as well) Example: a 40% v/v ethanol solution contains 40 mL ethanol per 100 mL total volume Slide 20 3.2 What are Solubility and Concentration? Also called volume percent or percent by volume, this is typically only used for mixtures of liquids. Percent by volume is simply the volume of the solute divided by the sum of the volumes of the other components multiplied by 100%: mixtures Slide 21 3.2 What are Solubility and Concentration? 4. Molarity : (mol/kg, mol, or m) denotes the number of moles of solute per kilogram of solvent ( not solution).moles kilogram Slide 22 3.2 What are Solubility and Concentration? Question: Explain the meaning of 12g/L. Slide 23 3.2 What are Solubility and Concentration? Solubility how easily a solute will dissolve in a solvent to make a solution When a substance will dissolve in a solvent, we say that it is soluble. If a substance will not dissolve, it is said to be insoluble. Slide 24 3.2 What are Solubility and Concentration? Examples: Rocks have very low solubility in water What are some other substances that are insoluble in water? Sugar is very soluble in water What are some other substances that are soluble in water? Slide 25 Investigation: How Does Temperature Affect Solubility? Complete the investigation on pg. 47 including the analyze and conclude sections and hand-in/email in your work. Slide 26 3.2 What are Solubility and Concentration? How can we increase solubility? By increasing the temperature Stirring Slide 27 3.2 What are Solubility and Concentration? How does soap work? Note that if particles of a solute are attracted to the particles of a solvent, they will diffuse throughout the solvent (the solute will dissolve) Example: oil does not dissolve in water because the particles of the two substances are not attracted to each other. On the other hand, particles of sugar are highly attracted to particles of water, so the solubility of sugar is high. Slide 28 3.2 What are Solubility and Concentration? Soap will dissolve in both water and oils because the sodium end of the soap molecule dissolves in water and the carbon end dissolves in oils. Cleaning with soap takes advantage of several separation techniques. Slide 29 Slide 30 Practice Questions: Hand-in/email Check your understanding questions from page 50 #3-5. Slide 31 3.3 Separating Mixtures Why might it be important to know how to separate mixtures? To help prevent illness from contaminated water In Canada, drinking water is generally safe because several precautions are taken to make it drinkable Slide 32 3.3 Separating Mixtures There are several methods to separate mixtures. These methods range from simple to complex. Slide 33 3.3 Separating Mixtures Mechanical separation One or more components are picked out of a mixture. For example, workers in a recycling plant make piles of different items; magnets remove metal in a scrap yard. Gold panning is also a form of mechanical separation. (See Did You Know on p. 50) Slide 34 3.3 Separating Mixtures In the late 1800s, Canadian farmers used a process called winnowing to separate wheat kernels from chaff (the wheat husk). Winnowing involved throwing the kernels and chaff into the wind. The lighter chaff was blown away, while the heavier kernels fell back into the container. This simple and effective method is still used in many parts of the world. Slide 35 Slide 36 3.3 Separating Mixtures Settling Density causes parts of the mixture to settle to the bottom. This may occur naturally as sedimentation, or be sped up using a centrifuge. During water filtration, contaminants sink and clear water is skimmed off. Slide 37 3.3 Separating Mixtures Flotation/coagulation Oil, detergents, or other chemicals are added to a mixture that is then aerated. This makes the desired component float (due to differences in densities) so it can be skimmed off the surface. The technique is often used in metal refining and in separating bitumen (tar) from sand. Coagulation is also used during water treatment. Slide 38 3.3 Separating Mixtures Filtration A mixture is passed through material with many holes. Anything larger than the hole is trapped while the rest of the mixture passes through. Slide 39 3.3 Separating Mixtures Solvent extraction A solvent is used to dissolve the desired component of the mixture. For example, soapy water dissolves the dirt on clothes so the dirt can be extracted; alcohol dissolves vanilla from vanilla seedpods, resulting in vanilla extract. Slide 40 3.3 Separating Mixtures Distillation A substance is heated to a specific temperature to vaporize a desired component which is then collected. This method can be used to desalinate water, extract pure oxygen from air, and separate the components of crude oil. http://www.footprints- science.co.uk/index.php?module=2&typ e=Fractional+distillation&section=Section1 &info=6 http://www.footprints- science.co.uk/index.php?module=2&typ e=Fractional+distillation&section=Section1 &info=6 Slide 41 3.3 Separating Mixtures Because different substances evaporate at different temperatures, the components of a complex mixture (such as petroleum) can be evaporated and collected as they condense. This process of fractional distillation is used to refine petroleum into fuel for your car, wax for candles, and asphalt for paving. In industry, alcohol (such as in liquor and disinfectants) is distilled in much the same way. Because ethyl alcohol boils at 78.5C, it can be evaporated and collected, leaving any water behind. Slide 42 3.3 Separating Mixtures Crystallization A dissolved solid is separated from a solution by cooling or concentrating the solution so the substance forms into crystals within the solution (e.g., growing crystals in sugar water). This method is used to remove salt from salt water. Slide 43 3.3 Separating Mixtures Chromatography This method is typically used to identify substances (e.g., in blood, drugs, and petroleum products) rather than to collect the substances for other uses. As the substance is drawn up the material (usually filter paper), it carries the solutes with it. The least dense solutes are drawn farthest up the filter paper; the most dense are deposited at lower levels of the paper. Slide 44 Compounds and Mixtures http://www.bbc.co.uk/bitesize/ks3/scienc e/chemical_material_behaviour/compou nds_mixtures/activity/ http://www.bbc.co.uk/bitesize/ks3/scienc e/chemical_material_behaviour/compou nds_mixtures/activity/ Slide 45 3.3 Separating Mixtures Purifying Water There is more than one method to purifying water. Example: One method involves adding alum to impure water. Bacteria, viruses, and tiny dirt particles stick to the alum particles making them very heavy. These heavy particles sink to the bottom, where they can then be separated from the water. Slide 46 3.3 Separating Mixtures Charcoal filters are used to remove dissolved impurities. However, the water that leaves the filters is still not clean and safe to drink. Water treatment plants add chlorine to drinking water. The chlorine kills bacteria. https://www.youtube.com/watch?v=9z14l5 1ISwg https://www.youtube.com/watch?v=9z14l5 1ISwg Slide 47 Separating Mixtures Animations http://www.s- cool.co.uk/gcse/chemistry/atomic- structure/revise-it/separating-mixtures http://www.s- cool.co.uk/gcse/chemistry/atomic- structure/revise-it/separating-mixtures Slide 48 3.3 Separating Mixtures Practice Questions Hand-in/Email Check Your Understanding questions on p. 55 #1-4 Slide 49 The End Complete Chapter 3 Assignment Review! Complete Chapter 3 Review on p. 56 #1-12