Slide 1 / 39 Slide 2 / 39 New Jersey Center for Teaching and Learning Progressive Science Initiative This material is made freely available at www.njctl.org and is intended for the non-commercial use of students and teachers. These materials may not be used for any commercial purpose without the written Solutions: permission of the owners. NJCTL maintains its website for the convenience of teachers who wish to Mixtures, Solubility and make their work available to other teachers, participate in a virtual professional learning Concentration community, and/or provide access to course materials to parents, students and others. Click to go to website: www.njctl.org www.njctl.org Slide 3 / 39 Slide 4 / 39 Mixtures vs. Pure Substances Solutions Mixtures contain two or more pure substances. Mixtures do not obey the law of definite composition therefore the relative amounts of each substance can vary depending on the sample. Pure water Salt water H 2 O contains H 2 O, Ca 2+ , Cl - , Na + ..... 89% O, 11% H composition by mass varies chemical separation method physical The infamous saltwater crocodile cannot survive in freshwater. It needs a mixture of water and many solutes. All mixtures can be separated using physical means while most pure substances cannot with the exception of thermal decomposition of certain pure substances such as metal carbonates and metal chlorates. What are some methods for physically separating mixtures? Slide 5 / 39 Slide 6 / 39 Mixtures Suspensions Mixtures are classified as suspensions, colloids, or solutions Due to their large particle size, suspensions can often be based on particle size. separated by filtration. When precipitates form a mixture of aqueous solutions, a Suspension Colloid Solution suspension is created with the solid precipitate settling out in an > 1000 nm 1000 nm <-->1 nm Particle Size < 1 nm aqueous medium. The solid precipitate can be easily separated by proper filtration. Settling Yes No No Homogenous No Yes Yes Tyndall Effect (particles Yes Yes No filtration precipitate + scatter light) Given the similarity between colloids and solutions, the Tyndall effect is often key to distinguishing them apart. Click here to see a short Other examples of suspensions include sand in water and animation of the Tyndall Effect snow in air.
Slide 7 / 39 Slide 8 / 39 Colloids Solutions Solutions contain the smallest solute particles that dissolve in a Due to their smaller particle size, colloids cannot be separated medium called the solvent. Solutions are homogeneous mixtures by filtration. In addition, the particles neither settle nor dissolve because regardless of sample size, the ratio of solute particles to in the greater medium. solvent remains the same. Fog is a classic example of a colloid, as the water droplets neither dissolve in the surrounding gaseous medium nor do Uniform mixture of solute (purple) and they settle out. solvent (green) The Tyndall Effect is easy to see when driving through fog as the light from the headlights gets scattered by the particles as visualized below by sunshine on a foggy morning. If you took a 5mL sample or a 200mL sample of a solution you would find the exact same ratio of solute to solvent. Slide 9 / 39 Slide 10 / 39 Solutions 1 Which of the following would be TRUE regarding mixtures? Solutions contain the smallest solute particles that dissolve in a medium called the solvent. Solutions are homologous mixtures A A sample of a mixture will never be uniform in because regardless of sample size, the ratio of solute particles to composition solven remains the same. Salt water is a classic example of a solution. The Na + and Cl - B They can be typically separated using only ions are dissolved in the solvent, creating a uniform material. chemical methods - C They vary in composition from sample to sample. Na+ - - Na+ - - + + + + + + - + + + Cl- + - + Na+ D Only solutions are considered true mixtures - + - + + - + Cl- + + + + Cl- + E None of these are true Due to their small size and interactions with the solvent, the solute particles cannot be filtered out. How could you physically separate solutes from solvents in a solution? Slide 11 / 39 Slide 12 / 39 2 A mixture cannot be separated by filtration and does 3 Which of the following physical methods is often not demonstrate the Tyndall Effect. Which of the employed to separate a suspension? following could this mixture be? A Distillation A NaCl(s) B Filtration B NaCl(aq) C Evaporation C Sand dissolved in water D Chromatography D Fog in the air E Lithography E Pure water
Slide 13 / 39 Slide 14 / 39 Solubility 4 Which of the following would NOT be TRUE of a solution? The solubility of a solute is defined as the amount of solute that A There are no interactions between the solute and can dissolve in a certain quantity of solvent. The solubility of a solute depends on its state and its affinity for the solvent. the solvent B Solutions cannot be separated by filtration Solubility is commonly expressed as g solute/100 g of solvent. C A sample of a solution will be uniform in Substance Solubility in water @23 C composition CH 3 OH infinite CH 3 Cl 0.47 g/100 g water D Solutions have smaller particles than do colloids and suspensions CCl 4 0.081 g/100 g water E Solutions do not demonstrate the Tyndall Effect Note: The more polar the molecule, the more affinity for water as it is also polar. CCl 4 is non-polar and therefore has an extremely small solubility in water. The phrase "like dissolves like" is applicable here. Slide 15 / 39 Slide 16 / 39 Solubility 5 Which of the following would likely be the LEAST soluble in water? The solubility of a solute in a solvent is highly temperature dependent. In general, solids and liquids dissolve better at higher temperatures while gases are more soluble at lower temperatures. A CO 2 Solubility of NaCl (g/100g water) at different temperatures. B HCl 0 C 10 C 50 C 80 C 100 C C PH 3 35.65 35.72 36.69 37.93 38.99 D CHCl 3 Solubility of NH 3 gas (mL/100 mL water) at different temperatures. 0 C 10 C 50 C 80 C 100 C E CH 3 OH 11.7 9.0 3.33 1.38 0.88 Note: The decrease in gas solubility with temperature can be explained by remembering that if the gas molecules have a high kinetic energy, they are likely to weaken any solute -solvent attraction and escape the solution. Slide 17 / 39 Slide 18 / 39 6 Which of the following would be most likely to 7 Which of the following is TRUE regarding solubility? dissolve in hexane (C 6 H 14 )? A O 2 gas would be more soluble at 10 C than 20 C A CH 3 OH B Polar substances are most miscible in non-polar B H 2 O solvents C Br 2 C In general, as the temperature increases, the solubility of most solids decrease D CH 2 Cl 2 D Solubility is not temperature dependent E NaCl E Solubility is not dependent on the polarity of the solute or solvent
Slide 19 / 39 Slide 20 / 39 Solubility 8 Which of the following would NOT be a miscible pair of solute and solvent? Saturated solutions contain the maximum dissolved solute at that temperature. Unsaturated solutions contain less and supersaturated solutions contain more. A KOH and H 2 O B CCl 4 and C 6 H 6 C CH 3 OH and H 2 O D CH 3 OH and CH 3 CH 2 OH Unsaturated Saturated Supersaturated E CH 3 OH and CCl 4 In a saturated solution, undissolved solute and dissolved solute are in equilibrium. In an unsaturated solution any new solute will dissolve whereas in a supersaturated solution, the amount of undissolved solute is growing. Slide 21 / 39 Slide 22 / 39 Solubility Curves Solubility Curves A solubility curve shows how much solute can dissolve in a certain The solubility curve for a given salt is difficult to predict. amount of solvent at a given temperature. 2 0 Solubility, grams per 100mL H Temperature in Celsius The line represents the amount of solute necessary for the dissolved and undissolved amounts to be in equilibrium - a saturated solution. Below the line the solution is unsaturated and above the line the solution is supersaturated. Slide 23 / 39 Slide 24 / 39 Solubility Curves Solubility Curves The solubility of a gas also depends on the pressure. The higher The solubility curves for gases clearly show the inverse relationship of gas solubility and temperature. the partial pressure of that gas above the liquid, the greater the solubility. This is known as Henry's Law. We can view the dissolved gas and undissolved gas above a solution as an equilibrium situation. Gas(dissolved) <--> Gas (undissolved) If the partial pressure of the undissolved gas is increased above a liquid, the equilibrium will shift left and more gas will dissolve. Gas(dissolved) <--> Gas (undissolved) Note: Cooler streams have higher dissolved oxygen (DO) Note: This is how soft drink manufacturers carbonate your soda. They simply levels than warmer streams therefore supporting a different crank up the partial pressure of CO 2 above the liquid and that causes more CO 2 variety of life. to dissolve. They then smack a lid on top so the pressure is maintained.
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