Definitions Solute-the substance being dissolved Solvent-the substance doing the dissolving (the larger amount) Solution- a homogeneous mixture of the solute and the solvent Solution= solvent + solute Aqueous (aq)= water solution Tincture= alcohol solution Amalgam= Mercury solution Molarity (M)- is the molar concentration of a solution measured in moles of solute per liter of solution. The molarity definition is based on the volume of the solution, NOT the volume of water. Vocab. Lesson Incorrect= The solution is 5.0 Molarity. Correct= The solution is 5.0 Molar. Example Problems Level 1- Given moles and liters Determine the molarity when 3.0 moles of sucrose are dissolved to make 2.0 liters of solution.
Level 2- Given Molarity and liters of solution Determine the number of moles of salt dissolved in 5.0 liters of a 0.50M solution of salt water.
cross multiply, X= 2.5 mols Level 3- Given grams (instead of moles) and liters of solution Determine the molarity when 117g of NaCl are dissolved to make 0.500 liters of solution. 1st convert to moles, 2nd plug into the molarity equation 117g NaCl( 1mol/58.5g)= 2.00mol NaCl
Level 4-Given grams (instead of moles) and milliliters of solution (instead of liters) Determine the molarity when 55.5g of CaCl2 are dissolved to make 250.mL of solution. 1st convert to moles, 2nd convert to liters, 3rd plug into the molarity equation 55.5g CaCl2( 1mol/111g)= 0.500mol CaCl2 250.ml( 1L/1000mL) =0.250L
Past Regents Questions-Follow link to check the answers Jan 2003-44 What is the molarity of a solution of NaOH if 2 liters of the solution contains 4 moles of NaOH?
Jan. 04-41 What is the molarity of a solution containing 20 grams of NaOH in 500 milliliters of solution? (1) 1 M (2) 2 M (3) 0.04 M (4) 0.5 M Jan 2002-42 What is the molarity of a solution that contains 0.50 mole of NaOH in 0.50 liter of solution?
Aug. 2006-42 How many total moles of KNO3 must be dissolved in water to make 1.5 liters of a 2.0 M solution? (1) 0.50 mol (2) 2.0 mol (3) 3.0 mol (4) 1.3 mol Aug 2005- 41 What is the total number of moles of NaCl(s) needed to make 3.0 liters of a 2.0 M NaCl solution?(1) 1.0 mol (3) 6.0 mol (2) 0.70 mol (4) 8.0 mol June 2006- 16 Molarity is defined as the(1) moles of solute per kilogram of solvent(2) moles of solute per liter of solution(3) mass of a solution (4) volume of a solvent Aug 2008- 15 Which phrase describes the molarity of a solution?(1) liters of solute per mole of solution(2) liters of solution per mole of solution(3) moles of solute per liter of solution (4) moles of solution per liter of solution June 2009-46 Which sample of HCl(aq) contains the greatest number of moles of solute particles? June 2007- 13 A 3.0 M HCl(aq) solution contains a total of(1) 3.0 grams of HCl per liter of water(2) 3.0 grams of HCl per mole of solution(3) 3.0 moles of HCl per liter of solution (4) 3.0 moles of HCl per mole of water June 2010-14 The molarity of an aqueous solution of NaCl is defined as the(1) grams of NaCl per liter of water(2) grams of NaCl per liter of solution(3) moles of NaCl per liter of water (4) moles of NaCl per liter of solution Jan 2008- 15 Which unit can be used to express solution concentration?(1) J/mol (3) mol/L (2) L/mol (4) mol/s Jan 04-41 What is the Molarity of a solution containing 20 grams of NaOH in 500 milliliters of solution?(1) 1 M (3) 0.04 M (2) 2 M (4) 0.5 M Jan 2010-40 What is the molarity of 1.5 liters of an aqueous solution that contains 52 grams of lithium fluoride, LiF, (gram-formula mass =26 grams/mole)?(1) 1.3 M (3) 3.0 M (2) 2.0 M (4) 0.75 M on to ppm or Molality back to Math of Chemistry Links Chemical Demonstration Videos
Now the #"moles of solute"# are a constant. The volume of solution MAY change substantially with increasing or decreasing temperature. In some calculations #"molality"# is used in preference, which is defined by the quotient.... #"molality"="moles of solute"/"kilograms of solvent"# ....this is temperature independent, and at lower concentrations, #"molarity"-="molality"#.
To get the molarity, you divide the moles of solute by the litres of solution. #"Molarity" = "moles of solute"/"litres of solution"# For example, a 0.25 mol/L NaOH solution contains 0.25 mol of sodium hydroxide in every litre of solution. To calculate the molarity of a solution, you need to know the number of moles of solute and the total volume of the solution. To calculate molarity:
EXAMPLE: What is the molarity of a solution prepared by dissolving 15.0 g of NaOH in enough water to make a total of 225 mL of solution? Solution: 1 mol of NaOH has a mass of 40.00 g, so #"Moles of NaOH" = 15.0 cancel("g NaOH") × "1 mol NaOH"/(40.00 cancel("g NaOH")) = "0.375 mol NaOH"# #"Litres of solution" = 225 cancel("mL soln") × "1 L soln"/(1000 cancel("mL soln")) = "0.225 L soln"# #"Molarity" = "moles of solute"/"litres of solution" = "0.375 mol"/"0.225 L" = "1.67 mol/L"# Some students prefer to use a "molarity triangle". It summarizes the molarity formulas as #"Moles" = "molarity × litres"# #"Molarity" = "moles"/"litres"# #"Litres" = "moles"/"molarity"#
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