Some more on solutions Concept map please use the following words to create a concept map relating to solutions... words: Solvent Solute Solutions Dissolving Dynamic equilibrium Crystalizing Temperature Pressure volume Be creative, you have 8 circles and a square to work with! Aqueous Solutions since water dissolves many substances easily, pure water never exists in nature water can dissolve other polar molecules and ions water containing dissolved substances are called aqueous solutions the dissolving medium is the solvent (what does the dissolving) *usually H20 Cont'd the dissolved particles are solute (what dissolves) examples: sodium chloride (salt) NaCl (s) sodium chloride dissolved in water NaCl (aq) solutions are homogeneous mixtures and are stable Cont'd solute particles may be ionic or molecular. They are usually polar, because non-polar molecules will not dissolve in water. However, solute particles will dissolve in other solvents. Ex. Grease in gasoline Solvation Water molecules, in continuous motion, collide with the solute particles placed in it. As a result, solvent molecules attract the solute particles causing the individual particles to break away from each other. This causes the crystal structure to break down and dissolving occurs. more particles become solvated ie. Surrounded by solvent molecules, due to attractions between the solute and solvent particles if the attractive forces between the particles in the crystal are greater than those with water the particles cannot be solvated – these compounds are insoluble in water eg. Barium sulphate or calcium carbonate continued nonpolar solvents such as gasoline will dissolve in non-polar compounds not because of attractive forces, but rather due to the lack of repulsion between the solvent and solute molecules General rule – Like Dissolves Like! Solution Formation Four factors affect the rate at which a solute dissolves: 1. Temperature (heat) 2. Agitation (stirring) 3. Particle Size 4. Nature of the particle (solubility) Temperature affects the amount of solute that can dissolve Stirring, particle size, and temp affect the rate at which the solute will dissolve example When 36 g of sodium chloride are added to 100g of water at 25º C, all the sodium chloride will dissolve. However, if one more gram of salt is added it will not dissolve no matter how vigorously it is stirred. Since water particles are in continuous motion they must collide with, and solvate, the solute particles explained.. The explanation: Particles are bombarded by water molecules. The water will release one particle as it collides with another. In turn, the water molecules pick up the new particle. There is no net change in the overall system as particles move from solution to solid and back again. A state of dynamic equilibrium exists between the solution and the undissolved solute. It's like stuffing people in the gymnasium, people out = people in... this is dynamic equilibrium The sodium chloride solution is said to be saturated A saturated solution contains: The maximum amount of solute that dissolves in a given quantity of a solvent at a given temp An unsaturated solution contains: Less solute than a saturated solution Solubility This is the maximum amount of solute that can dissolve in a particular volume of solvent at a particular pressure and temperature solute is expressed in grams of solute/100 mL of solvent every pure substance has its unique solubility Solubility ranking Solubility Table: a reference for how ionic compounds will behave when added to water - based on the cut off points between very soluble (0.1>mol/L ) to slightly soluble (< 0.1 mol/L) Comparing the Solubility of Different Phases of Matter (in an aqueous environment) Solids as a rule.. Solubility of Solids Have higher solubility in water at higher temperatures Gases as a rule... Solubility of Gases Have higher solubility in water at lower temperatures (opposite that of solids) Have higher solubility in water at higher pressures Liquids as a rule... Solubility of Liquids For polar liquids, the solubility usually increases with temperature Mostly non-polar liquids, do not dissolve in water to any appreciable extent but form a separate layer. Liquids that behave in this way are said to be immiscible Examples: Olive oil and water sometimes... Some liquids (such as those containing small polar molecules with hydrogen bonding (methanol for example), dissolve completely in water (never become saturated) and are said to be miscible Examples: Ethanol and soda pop Elements as a rule... Elements Generally have low solubility in water Halogens and oxygen dissolve in water to only a very tiny extent but they are so reactive that even in tiny concentrations, they are often very important in solution reactions check Based on our knowledge of solution formation and solubility, What happens when the temperature of a saturated solution is raised? Can we add more solute or will excess solute become undissolved? answer We can add excess solute to the solution and it will dissolve From last week... What is a supersaturated solution? answer... A solution which contains more solute than it can theoretically hold Ex: Perrier or beer (CO2 in water) crystallization.. Crystallization can be initiated in a supersaturated solution: A supersaturated solution has more solute than a saturated solution, and yet the solute is able to remain in solution. It is UNSTABLE. If a few crystals of solute are added to serve as particles on which crystallization can occur, the excess solute crystallizes quickly. Practice Questions Give examples of two liquids that are immiscible and two that are miscible with water. Can more oxygen dissolve in a litre of water in a cold stream or a litre of water in a warm lake? Include your reasoning. State why you think clothes might be easier to clean in hot water. Why do carbonated beverages go “flat” when opened and left at room temperature and pressure? a) The solubility of oxygen in blood is much greater than its solubility in pure water. Suggest a reason for this observation. b) If the solubility of oxygen in blood were the same as in pure water, how would your life be different? c) Is there an advantage for animals that are cold blooded? Explain briefly. For any solute, what important condition must be stated in order to report the solubility problem... 1. In a chemical analysis experiment, a student notices that a precipitate has formed, and separates this precipitate by filtration. The collected liquid filtrate, which contains aqueous sodium bromide, is set aside in an open beaker. Several days later, some white solid is visible along the top edges of the liquid and at the bottom of the beaker. What does the presence of the solid indicate about the nature of the solution? equlibrium Write a brief theoretical explanation for this equilibrium mixture. State two different ways to convert the mixture of the solid and solution into a homogeneous mixture. Fishy thinking... Different species of fish are adapted to live in different habitats. Some, such as carp, can survive perfectly well in relatively warm, still water. Others, such as brook trout, need cold, fast-flowing streams, and will die if moved to he carp’s habitat. Describe and explain the oxygen conditions in the two habitats. More fish Hypothesize about the oxygen requirements of the two species of fish.