Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Solutions and Molarity Solutions ► The solute is the substance dissolved in the solution ► The solvent is the substance in which the solute is dissolved ► Aqueous Solution is a solution in which the solvent is water ► ► Heterogeneous Mixture: A mixture in which the composition is not uniform throughout Sand and water A salad Oil and water Homogeneous Mixture: A mixture in which the composition is uniform throughout May be solids, liquids and/or gases Also called a solution Salt and water Ice tea mix and water Solutions ► What is an ionic substance? A bond between a metal and a non-metal The metal gives up one or more electrons to the non-metal and becomes positively charged The non-metal accepts one or more electrons and becomes negatively charged. The two ions are held together by electrostatic attraction [Na+][Cl-] Solutions ► Ionic substances readily dissociate (come apart) in water. ► The positive and negative ions become attracted to individual water molecules ► Salt dissolving ► Ionic equation for salt dissolving in water: NaCl -> Na+ + Cl- Solutions ► ► ► ► An electrolyte is a substance, when dissolved in water, conducts electricity A strong electrolyte is a solute that produces many ions in water (sodium chloride) A weak electrolyte is a solute that produces only a few ions in water A non-electrolyte does not dissociate into ions in water and does not conduct electricity (sucrose) Conversions ► 1000 ml = 1 L (liter) ► To convert from ml to L, divide by 1000 ► To convert from L to ml, multiply by 1000 ► 350 ml = ? L ► 350 ml = .350 L ► 1.7 L = ? ml ► 1.7 L = 1700 ml Molarity ► Molarity is an expression of solution concentration ► Molarity = moles of solute/liter of solution ► Steps for calculating molarity Convert volume from ml to L (if necessary) Determine the molarity by dividing the number of moles of solute by the solution volume in liters ► Volumetric flasks Molarity ► 100.5 ml/1000 = .1005 L ► Molar mass of glucose = 180.16 g/mol ► 5.10 g/180.16 g/mol = .03 mol glucose ► .03 mol/.1005 L = .29 mols per liter ► .29 M Molarity ► Practice Problem #1: .15 M ► Practice Problem #2: .13 M ► Practice Problem #3: .008 M Preparation of Solutions ► Convert ml to L (if necessary) ► Determine molar mass of solute ► Set up a proportion ► Solve to get number of moles of solute needed ► Multiply that number by the molar mass of the solute. Preparation of Solutions ► Example 1: ► 0.1 M means .1 mol/1 Liter Convert to L -> 100.0 ml/1000 = 0.10 L Molar mass NaOH = 40 g/mol Proportion -> .1mol/1 L * x mol/.1 L X = .01 mol of NaOH .01 * 40.0 g/mol = 0.4 g Preparation of Solutions Alternate ► Convert ml to L (if necessary) ► Determine molar mass of solute ► Multiply all the numbers: Liters x mols/liter x molar mass ► Example 1: 0.10 L x .1 mol/1 Liter x 40.0 g/mol = 0.4 g Preparation of Solutions ► Practice 11.1 80.0 11.1 30.0 g g g g Problems CaCl2 NaOH CaCl2 NaOH Dilutions Solutions you work with in the lab (dropper bottles) are made by diluting premixed concentrated stock solutions. ► By adding additional solvent to concentrated solutions decreases the ratio of solute to solvent particles. ► Use the following relationship to calculate the volume of solvent you may need M1V1 = M2V2 M1V1 represent the molarity and volume of the stock solution M2V2 represent the molarity and volume of the dilute solution Remember to convert ml to L ! ► Dilutions ► Example problem 2.00 M * V1 = 0.300 M * 0.50 L 2.00 M * V1 = 0.150 Solve for V1 = 0.150/2.00 V1 = .075 L or 75.0 ml Dilutions ► Practice Problems V1 = 0.125 L or 125 ml V1 = .005 L or 5.0 ml M2 = .7 M