Understanding Concentration and Dilution of Solutions by Dr. Laila Al-Harbi
Dr. Laila Al-Harbi explains the concept of concentration of solutions, focusing on molarity and the calculation involved. The molar concentration of solutions is determined by the amount of solute in a given volume of solvent, expressed as moles of solute per liter of solution. Additionally, the process of dilution is discussed, highlighting how to prepare less concentrated solutions by adding solvent while keeping the number of moles of solute constant.
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4.5 Concentration of solutions dilution of solutions Dr.Laila Al-Harbi
The concentration of a solution is the amount of solute present in a given amount of solvent , it can be expressed in terms of its molarity (molar concentration) moles of solute volume of solution in liters moles of solute volume of solution in liters Molarity ( Molarity (M M) ) = Have mol and vol molarity Have molarity and vol mol of solute Have molarity and mol of solute volume AND: mol of solute grams of solute Dr.Laila Al-Harbi
n M = V Given: n & M V Given: n & V M Given: V & M n m = = n m nMM MM 3
What is the molar concentration of 0.730 mol glucose C6H 12O6 in 500 ml solution C6H 12O6 = 0.730 mol C6H 12O6x 1000 mL soln 500 mL 1L soln = 1.46 M 1.46 M C6H 12O6 Dr.Laila Al-Harbi
3.81g 3.81g Dr.Laila Al-Harbi
What is the molarity of an 85 ml ethanol C2H5OHsolution containing 1.77g of ethanol? What is the volume (in ml) of 0.315M NaOH solution contains 6.22g of NaOH? Molar mass NaOH= 40g Molar mass C2H5OH = 46.068g n = 1.77g/ 46.068= 0.038 mol n = 6.22g /40g= 0.1555 mol v=n/M= 0.1555 mol / 0.315M M=n/v= 0.038 mol/ 85 ml v= 0.494 = 494 ml M= 0.452 M Practice exercise 4.6 Practice exercise 4.7 Dr.Laila Al-Harbi
Dilution concentrated solution from a more concentrated solution. Calculation based on that the number of moles of solute is constant we add only solvent Dilution is the procedure for preparing a less Calculation based on that the number of moles of solute is constant we add only solvent Dilution Add Solvent = = Moles of solute before dilution (i) Moles of solute after dilution (f) MfVf MiVi Dr.Laila Al-Harbi
How many mL of 5.0 M K2Cr2O7 solution must be diluted to prepare 250 mL of 0.10 M solution? M Mi i = Mi = 5.0 = 5.0M M V Vf f = 250 MfVf/Vi = 250 mL Vi = 250 ml 0.1M/5ml = 5 ml mL V Vi i = ? = ? M Mf f = = 0.10 0.10M M 5 ml If 10.0 mL of a 10.0 M stock solution of NaOH is diluted to 250 mL, what is the concentration of the resulting solution? V Vi i= 10.0 M Mf f= ? = ? = 10.0 mL mL M Mi i = 10.0M = 10.0M V Vf f = 250 = 250 mL mL Mi= MfVf/Vi Mi = 10ml 10M/250ml = 0.4 ml 0.4 ml Dr.Laila Al-Harbi
How would you prepare 60.0 mL of 0.200 M HNO3 from a stock solution of 4.00 M HNO3? MiVi = MfVf Mi = 4.00 Vi = ? ml Mf = 0.200 Vf = 60 ml Vi =MfVf =0.200 x 60 4.00 = 3 mL Mi Dr.Laila Al-Harbi
Practice exercise 4.9 How would you prepare 200 mL of 0.866 M NaOH from a stock solution of 5.07 M NaOH? MiVi = MfVf Mi = 5.07 Vi = ? ml Mf = 0.866 Vf = 200 ml Vi =MfVf =0.866 x 200 5.07 = 34.2 mL Mi Dr.Laila Al-Harbi
Problem 4.74 (page 163) Problem 4.74 (page 163) M1 = 0.568 M V1 = 46.2 mL = 46.2 10-3 L moles for the first Ca(NO3)2 solution (n1) = M1 V1 = 0.568 M 46.2 10-3 L = 0.026 mol Calculation based on that we have two solutions with different number of moles mixed together , then we will calculate the molarity of the new solution Calculation based on that we have two solutions with different number of moles mixed together , then we will calculate the molarity of the new solution M2 = 1.396 M V2 = 80.5 mL = 80.5 10-3 L moles for the second Ca(NO3)2 solution (n2) = M2 V2 = 1.396 M 80.5 10-3 L = 0.112 mol Total moles of Ca(NO3)2 in the final solution = n1 + n2 = 0.026 + 0.112 = 0.138 mol Total volume of the final solution = V1 + V2 = (46.2 10-3 L) + (80.5 10-3 L) = 126.7 10-3 L The concentration of the final solution Mf = n/V = 0.138 mol / 126.7 10-3 = 1.09 M Dr.Laila Al-Harbi
moles of solute volume of solution in liters moles of solute volume of solution in liters Molarity Molarity ( (M M) ) = Molarity ( Molarity (M M) ) moles of solute = mass / molar mass moles of solute = mass / molar mass volume of solution in liters volume of solution in liters Dr.Laila Al-Harbi
