Transcript Unit 8
Solutions and Solubility Essential Questions 1. What’s a solution vs mixture? 2. What’s the difference between a solution, solvent and solute? 3. Can do you quantify concentration? 4. What do some things dissolve while others do not? 5. How can we increase the rate that something dissolves? What happens when stuff dissolves? http://www.youtube.com/watch?v=0cPFx0 wFuVs Mixtures and Solutions Remember back to the beginning of the year when we learned about mixtures! Concept check: Identifying Mixtures Identify the follow as homo or heterogenous: Milk Oil Muddy water Iron Brass Blood Paint Water Soda Sugar water Flat Soda Toothpaste Heterogeneous Mixtures There are two types of heterogeneous solutions: Suspensions: mixtures containing particles that will settle out if left undisturbed. Examples: oil and water, sandy water, muddy water, paint, and flour in water Colloids: mixtures of smaller sized particles that do not settle out on their own Examples: milk, blood, butter, smoke, spray deodorant, motor oil Homogenous Mixtures Also called solutions Can be solids, liquids or gases Single phase Remain mixed; particles DO NOT settle out Cannot be separated by filter paper Solutions A solution is formed when a solute dissolves in a solvent forming a homogeneous mixture Solutions Solvent – present in the greatest amount Solute – present in the lesser amount Solution – Mixture of 2 or more substances that are a mixed homogeneously Identify the solvent and solute? Solution Flat Soda Solvent Water Solute Sugar syrup Lemonade Water Lemonade mix Alloy like brass Copper Zinc Air Nitrogen Oxygen Antifreeze Water Antifreeze Ocean Water Water salt Antifreeze Close up In 1885 Karl Benz of Germany invited the first radiator for cars Before this, car engines were cooled with water and needed to be constantly refilled! Antifreeze has ethylene glycol added to water to elevate the boiling point and depress the freezing point Solvent Joke WATER AS A SOLVENT Water is the most effective solvent Water will dissolve many ionic compounds and most polar covalent compounds Water is not effective as a solvent for non-polar covalent compounds Effectiveness of water is because water is highly polar with hydrogen bonds WATER AS A SOLVENT-HYDROGEN BONDING The bond formed between an oxygen atom from one water molecule and a hydrogen atom from another water molecule Image used courtesy of CINCH ® Learning Polarity Demonstration Image used courtesy of: http://www.glogster.com/arooke2/hydrogen-bonds/g6m99vd692fc7hgidt985ta0?old_view=True Concentration The concentration of a solution is usually described as concentrated or dilute There are many ways to express concentration: Concentration as Percent by Mass Ratio of the solutes mass to the mass of the solution expressed as a percentage! Amount of solution = solute + solvent percent by mass = amount of solute x 100 amount of solution Concentration as percent by mass 1) What is the percent by mass if 2 grams of sugar is added and dissolved in 10 grams of water? 16.7% Concentration as percent by mass 2) In order to maintain a sodium chloride (NaCl) concentration similar to ocean water, an aquarium must contain 3.6 g NaCl per 100.0 g of water. What is the percent by mass of NaCl in the solution? 3.5% Concentration as MOLARITY Another common unit of concentration used by chemist is molarity Molarity = the solutions concentration measured as moles of solute per liter of solution Molarity = Moles of solute Liters of solution Units of M = Moles / Liter Concentration as Molarity 1) How much sucrose, in moles, is there in 0.5 liters of a 2-molar (2M) solution? 1 mole Concentration as Molarity 2) To make a 4.0 M solution, how many moles of solute will be needed if 12 L of solution are required? Concentration as Molarity 3) 116.88 grams of NaCl are dissolved in 1.5 liters of solution. What is the molarity of this solution? First, convert grams of NaCl to moles NaCl Found by dividing 116.88g by the molar mass of NaCl, 58.44 g/mol 116.88g NaCl is 2.00 moles of NaCl Next, divide moles solute by liters of solution 2.00 moles NaCl = 1.33 mol NaCl/L = 1.33 M NaCl 1.5 L Practice Try the following calculating concentration as percent by mass and molarity problems Dilution What does it mean to dilute a solution? Dilution In the lab, sometimes reactions call for different strengths or concentration of solutions in order for a reaction to occur. We use molarity to create solutions with the proper concentrations. Often we need to dilute a stronger solution to a weaker one. DILUTION Solutions can be diluted simply by adding more solvent and leaving the amount of solute unchanged What happens to molarity when a solution is diluted? More water has been added, so the total volume of solution is greater but the amount of solute is the same Molarity will decrease! Dilution We use the following equation to perform dilution calculations: M1V1=M2V2 M1=Initial molarity V1= Initial volume M2= Final molarity V2=Final volume DILUTION EXAMPLE 1) What would be the resulting molarity of 2.500 L solution when the starting solution had a molarity of 6.00 M and a volume of 417 mL? M1= 6.00 mol/L V1= 417 mL M1V1=M2V2 M2= ?? V2= 2500 mL (6.00 mol/L)(417 mL) = (M2)(2500 mL) (M2) = (6.00 mol/L)(417 mL) (2500 mL) M2 = 1.00 mol/L Dilution 2) If I have 340 mL of a 0.5 M NaBr solution, what will the concentration be if I add 560 mL more water to it? 0.19 M (the final volume is 900 mL, set up the equation from that) STOP Work on some problems on your own CONCENTRATION AND SOLUBILITY The amount of solute affects both solubility and dissolving rate. A solvent can only dissolve so much solute. As the concentration increases, the ability to dissolve more decreases, as does the rate at which it will dissolve. Solution Concentration Unsaturated When the amount of solute is less than the maximum that could be dissolved Saturated When a solution holds the maximum amount of solute Fats! You’ve all heard that we should avoid saturated fats…so what does that mean? Saturated fats (butter, dairy products, meat) are solid at room temperature and are evenly filled out with hydrogen. They increase the levels of bad cholesterol (LDL) and clog your arteries. Mono and poly unsaturated fatty acids (corn oil, sunflower oil, and soybean oil, while omega 3 is present in salmon, trout and tuna) remain liquid at room temp and increase the levels of good cholesterol! Solution Concentration Supersaturated When a solution holds more than the maximum amount and is thus unstable! Supersaturated demo http://www.youtube.com/watch?v=1y3bKI Okcmk SOLUBILITY CURVES Show the amount of solute that can dissolve in a solvent under normal circumstances at a given temperature The line for a given element on a set of solubility curves is called the saturation line Factors affecting Solvation (aka rate of Dissolving) Solvation: The act of surrounding solute particles with solvent particles to form a solution! The solute is being pulled apart and surrounded by the solvent. Soluble – if you can dissolve any of the solute Insoluble – if you can’t dissolve any We can change this by changing many different factors! Factors Affecting Solvation The rate at which the solute dissolves in the solvent (link to KMT) As Kinetic Energy increases, dissolving rate increases As Kinetic Energy decreases, dissolving rate decreases As the number of collisions increases, dissolving rate increases As the number of collisions decreases, dissolving rate decreases (1) TEMPERATURE AND DISSOLVING RATE Increasing the temperature speeds up the movement of its particles Allows for more collisions between solute particles and solvent particles (2) SURFACE AREA AND DISSOLVING RATE Breaking a solid into smaller pieces greatly increases its surface area More solvent particles can come into contact with more particles of the solute corresponding to increased surface area Rate of collisions increases as surface area increases (3) AGITATION AND DISSOLVING RATE Agitation Stirring, Mixing, Shaking As agitation speed increases, rate of dissolving increases As the solvent moves around, more collisions occur between solvent and solute particles SUMMARY OF FACTORS AFFECTING DISSOLVING RATES As temperature ↑, dissolving rate ↑ As particle size ↓, surface area↑, dissolving rate ↑ As agitation ↑, dissolving rate ↑ LAB Factor’s affecting solubility lab SOLUTIONS & SATURATION Unsaturated Saturated Supersaturated Definition More solute can dissolve in the solvent No more solute will dissolve in the solvent. If there is extra undissolved solute, it will settle to the bottom of the container. Under unusual circumstances more solute is dissolved in solvent than it can normally hold Solubility Curve Below the saturation line On the saturation line Above the saturation line No No, it is already past saturation point Can you Yes Dissolve More Solute? SOLUBILITY CURVE Let’s practice reading a solubility curve! FACTORS AFFECTING SOLUBILITY 1. Temperature 2. Pressure 3. Polarity FACTORS AFFECTING SOLUBILITY (1) Temperature Solids and Liquids: Generally, as temperature increases, the solubility of solids and liquids increases – why? As temperature ↑, solubility ↑ Gases: Generally, as temperature increases, the solubility of gases decreases – why? As temperature ↑, solubility ↓ FACTORS AFFECTING SOLUBILITY (2) Pressure Solids and Liquids: no effect – why? As pressure ↑, solubility is unaffected Gases: Generally, as pressure increases, the solubility of gases increases – why? As pressure ↑, solubility of gases ↑ FACTORS AFFECTING SOLUBILITY (3) Polarity!! The nature of the solvent affects solubility Like Dissolves Like Ionic compounds, if they are soluble, dissolve in polar solvents Polar molecular (covalent) compounds dissolve in polar solvents Non-polar molecular (covalent) compounds dissolve in non-polar solvents