Concentration of Solutions Concentration of a Solution- amount of solute present in a given quantity of solvent or solution. Image from http://pharmaxchange.info/press/wp-content/uploads/2011/02/31-600x366.jpg Concentrated- solution that contains large amounts of solute Dilute- solution contains relatively small amounts
Concentration of solutions (cont.) Most useful way to describe the concentration is, Molarity (M). Molarity can also be called Molar Concentration. Ex. 6M = 6-molar solution Molarity is the number of moles of solute per liter of solution.
Concentration The measure of how much solute is dissolve in a specific amount of solvent or solution. Concentrated large amount of solute high Molarity Diluted small amount of solute low Molarity
Molarity = Molarity ( M ) moles solute liters of solution The number of moles of solute dissolved in per liter of a solution. Molarity = moles of solute = mol liters of solution L Volume must be converted to Liters (L) Molarity ( M ) = moles solute liters of solution
Example: Calculate Molarity Calculate the molarity of 0.35 moles of sodium sulfate (Na2SO4) dissolved in 1.5 L solution. Find your equation: Substitute known values: M= mol L 0.35 mol Na2SO4 1.5 L solution M= M= 0.23 M Na2SO4
Class Practice What is the molarity of 65g of KCl if 90 mL of solution are formed? 1) Convert grams to mol = .87 mol 2) Convert mL to L (90 mL/1000) = 0.09 L 3) Calculate molality = mol/liters = .87mol//.09 L = 9.67 M 65 g KCl 1 mol KCl 74.6 g KCl REMEMBER: M is the same as writing mol L
Calculating Molarity What is the molarity of an aqueous solution containing 40.0 g of glucose (C6H12O6) in a 1500 ml solution? If given 340 g of CuCl2, what would be the molarity of the solution if it was dissolved in 6425 cm3 of water? Note: (1 cm3 = 1 ml)
Practice Problems (to turn in) 1) .25 mol of NaCl is dissolved in 200.0 mL of water, calculate the molarity. 2) 525 mL of water dissolves 1.5 mol of FeO2, calculate the molarity. 3) What is the molarity of the following solutions? a) 15.25 g MgCl2 in 500 mL of solution b) 2.48 g CaF2 in 375 mL of solution 4) 15.8 g of KCl is dissolved in 225 mL of water. Calculate the molarity. 5) Calculate the volume of 0.30M KCl solution that contains .05 mol of KCl
Molarity and dilutions Molarity is important for calculating changes in the concentration as a solution is diluted In dilutions solute stays the same as solvent is added Diluting a solution reduces the number of solute per unit of volume, but the total number of moles in a solution stays the same. Molarity of solute Molarity of solute after dilution before dilution =
Calculating Dilutions The final solution will have a larger volume but lower concentration, and the moles of te solute present will be the same after as before the dilution. The relationship can be expressed with the following equation: M1V1=M2V2
Example 1: Calculating Dilutions Suppose a .2L solution of 15-molar sulfuric acid (H2SO4) was diluted to a volume of 1.0L. What would the resulting concentration be? 1st step identify the variables: M1= 15M H2SO4 = 15 mol H2SO4 /L V1= 0.2L M2= ? V2=1.0 L
Example 1: Calculating Dilutions Suppose a .2L solution of 15-molar sulfuric acid (H2SO4) was diluted to a volume of 1.0L. What would the resulting concentration be? 2nd step Rearrange 3rd step substitute the formula: and solve : M1V1=M2V2 M2= 15 mol H2SO4 /L x 0.2L 1.0L M2= M1V1 V2 M2= 3M H2SO4
Example 2: Calculating Dilutions If I have a container of a concentrated 6.0M sodium hydroxide (NaOH), and I want to prepare 450mL of 0.10M Sodium Hydroxide, How much of the concentrated solution will I need to use? 1st step identify the variables: M1= 6M NaOH = 6 mol NaOH/L V1= ? M2= 0.10M NaOH V2=450mL= 0.450L
Example 2: Calculating Dilutions If I have a container of a concentrated 6.0M sodium hydroxide (NaOH), and I want to prepare 450mL of 1.0M Sodium Hydroxide, How much of the concentrated solution will I need to use 2nd step Rearrange 3rd step substitute the formula: and solve : M1V1=M2V2 V1= 1.0M NaOH x 0.450L 6M NaOH V1= M2V2 M1 V1= 0.075L or 75ml