Transcript Document
UNIT 8, PART I - SOLUTIONS AND SOLUBILITY KEY TERMS Anion - A negatively charged ion Aqueous Solution - A solution where water is mixed with something to make a solvent Cation - A positively charged ion Concentration - The amount of solute per unit volume of solution Dilution - Weakening or reducing the concentration Molarity (M) - Concentration measured by the number of moles of solute per liter of solution Insoluble - Incapable of being dissolved Polarity - A separation of electric charge leading to a molecule having an electric dipole Saturated Solution - A solution that contains the maximum amount of solute at a given temperature KEY TERMS Solubility - The quantity of a particular substance that can dissolve in a particular solvent Solubility Curve - A graph showing the relationship between solubility and temperature Soluble - Able to be dissolved Solute - The dissolved matter in a solution Solvent - Able to dissolve other substances Unsaturated Solution - A solution that contains less than the maximum amount of solute at a given temperature 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 Used courtesy of: http://www.volusia.org/services/public-works/water-resources-and-utilities/ WATER AS A SOLVENT – POLARITY (IT IS THE KEY) Image used courtesy of: http://www.ecfs.org/projects/prepole/MARINE%20BIOLOGY%2012/Chapter%20Readings/Ch%201%20Oceanography/Chapter%201%20Notes.htm WATER AS A SOLVENT- HYDROGEN BONDING The powerful attraction between an oxygen atom from one water molecule and a hydrogen atom from another water molecule Image used courtesy of CINCH ® Learning Image used courtesy of: http://www.glogster.com/arooke2/hydrogen-bonds/g-6m99vd692fc7hgidt985ta0?old_view=True SOLUBILITY The ability to dissolve a solute in a solvent to form a solution, a homogeneous mixture Solute – The matter dissolved in a solvent Solvent – The matter in which a solute is dissolved Solution – Homogeneous mixture TYPES OF SOLUTIONS FACTORS AFFECTING SOLUBILITY It is all about 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 FACTORS AFFECTING SOLUBILITY Factors affecting the solubility of solids and liquids Temperature Generally, as temperature increases, the solubility of solids and liquids increases Factors affecting the solubility of gases Temperature Generally, as temperature increases, the solubility of gases decreases Pressure Generally, as pressure increases, the solubility of gases increases SUMMARY OF FACTORS AFFECTING SOLUBILITY Temperature As temperature ↑, solubility of liquids and solids↑ As temperature ↑, solubility of gases↓ Pressure As pressure ↑, solubility of liquids and solids is unaffected As pressure ↑, solubility of gases ↑ SUMMARY OF FACTORS AFFECTING SOLUBILITY Nature of Solvent Generally the nature of the solvent will determine what kinds of matter will dissolve in it. Polar solvents (such as water) will generally dissolve polar compounds. Non‐polar compounds will generally dissolve non‐polar compounds. 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 LIKE DISSOLVES LIKE! 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 DISSOLVING RATE The rate at which the solute dissolves in the solvent 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 DISSOLVING RATE Factors affecting dissolving rate Temperature As temperature increases, dissolving rate increases Surface Area As surface area increases, particle size decreases As surface area increases, dissolving rate increases Agitation As agitation increases, dissolving rate increases TEMPERATURE AND DISSOLVING RATE Since temperature is a measurement of the average kinetic energy, changing the temperature by adding or removing heat will change the rate of dissolving. Increasing the temperature speeds up the movement of its particles The change in temperature will affect both the number of collisions and the probability that as particles collide the solute will dissolve in the solvent. Allows for more collisions between solute particles and solvent particles Used courtesy of: http://www.seriouseats.com/2012/10/ask-the-food-lab-on-hot-chocolate-and-whole-wheat.html 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 AGITATION AND DISSOLVING RATE Agitation is the result of an external force causing the motion of the solute and the solvent such that there is an increased chance of collision. Stirring, Mixing, Shaking As agitation speed increases, rate of dissolving increases As the solvent moves around, more collisions occur between solvent and solute particles Used courtesy of: http://www.pennlive.com/lehighvalley-generalent/index.ssf/2008/06/in_defense_of_koolaid.html SUMMARY OF FACTORS AFFECTING DISSOLVING RATES As temperature ↑, dissolving rate ↑ As particle size ↓, surface area↑, dissolving rate ↑ As agitation ↑, dissolving rate ↑ 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 rate at which it will dissolve decreases. CONCENTRATION OF SOLUTIONS Concentration – the degree to which a solution contains the maximum amount of solute. Directly related to density Qualitative Uses terms saturated and unsaturated to reference the amount of solute dissolved in the solvent Quantitative Molarity – the number of moles dissolved in one liter of solution SOLUTIONS AND SATURATION • Saturated Solution – A solution is considered saturated when it contains the maximum amount of solute given the volume and environmental conditions of the solvent. • Unsaturated Solution – Any solution into which more solute can be dissolved is unsaturated. • An unsaturated solution that is close to the point of saturation is referred to as “concentrated”. • An unsaturated solution well below the point of saturation is referred to as “dilute”. • Super‐Saturated Solution – Any solution that contains more dissolved solute than it could contain under normal conditions is super‐saturated. • A beverage with carbonated water is a supersaturated solution. It is packaged into cans or bottles under conditions of high pressure. When the can or bottle is later opened, the carbon dioxide bubbles out of solution under the lower pressure. • Rock candy is made using a supersaturated solution of sugar and allowing the sugar crystals to slowly form on a string dipped in sugar. SOLUTIONS & SATURATION Unsaturated Saturated Supersaturated Definition Contains less than the maximum amount of solute. More solute can dissolve in the solvent Contains the maximum amount of solute. No more solute will dissolve in the solvent. If there is extra undissolved solute, it will settle to the bottom of the container. Contains more dissolved solute than the maximum under normal conditions Solubility Curve Below the saturation line On the saturation line Above the saturation line Can you Dissolve More Solute? Yes No No, it is already past saturation point Imaged used courtesy of: http://www.mts.net/~alou/Chemistry%2011/Unit%204%20-%20Solutions%20Lessons/Lesson%203%20-%20Factors%20Affecting%20Solubility.htm 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 Comparisons are made using the line for a given compound Under the curve – the solution is unsaturated Above the curve without excess – the solution is supersaturated Above the curve with excess – the solution is saturated On the curve – the solution is saturated SOLUBILITY CURVES QUANTITATIVE SOLUBILITY: MOLARITY Measured as moles of solute per liter of solution Molarity = Moles of solute Liters of solution M = Moles Liter MOLARITY EXAMPLE 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 DILUTION What does it mean to dilute a solution? Solutions can be diluted simply by adding water 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! 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 What would be the resulting molarity of 2.5 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 (6.00 mol/L)(417 mL) = (M2)(2500 mL) (M2) = (6.00 mol/L)(417 mL) (2500 mL) M2 = 1.00 mol/L M2= ?? V2= 2500 mL DISSOCIATION AND DISPERSION Dissociation – When ionic compounds dissolve, they separate into the ions that were bonded together. Example: Potassium sulfate will dissociate into potassium ions and sulfate ions. K2SO4 → 2K1+ + SO42 More examples of dissociation: NaCl → Na1+ + Cl 1 MgCl2 → Mg2+ + 2 Cl1 Al2(SO4)3 → 2 Al3+ + 3SO42- Dispersion – When complete dispersion occurs, the molecules of the solute are uniformly mixed with the molecules of the solvent. This occurs with covalent compounds. ELECTROLYTIC SOLUTIONS Electrolytic solutions conduct an electrical current Ions dissociate when dissolved in water Ions, because they are charged particles, act as a path for the flow of electricity The more ions present, the more electrolytic the solution is Non-electrolytic solutions do not conduct an electrical current ELECTROLYTIC SOLUTIONS Electrolyte Soluble Ionic Solute Non-Soluble Ionic Solute Non-Soluble Covalent Solute Yes No No CONTROLLING ELECTROLYTIC SOLUTIONS In order to increase the electrolytic properties of a solution you must increase the concentration of ions present in the solution Reduce the volume of the solution while maintaining the amount of electrolytic solute Increase the amount of electrolytic solute without modifying the volume Using a different electrolytic solute which produces more ions when it dissociates In order to decrease the electrolytic properties of a solution you must decrease the concentration of ions present in the solution Dilute the electrolytic solution Using a different electrolytic solute which produces less ions when it dissociates