| 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
Interestingly enough, I'm not getting #"0.0341% w/v"# either. Here's why. Start by calculating the percent composition of chlorine, #"Cl"#, in calcium chloride, This will help you calculate the mass of chloride anions, #"Cl"^(-)#, present in your sample. To do that, use the molar mass of calcium chloride, the molar mass of elemental chlorine, and the fact that #1# mole of calcium chloride contains #2# moles of chlorine atoms.
This means that for every #"100 g"# of calcium chloride, you get #"63.89 g"# of chlorine. As you know, the mass of an ion is approximately equal to the mass of the neutral atom, so you can say that for every #"100 g"# of calcium chloride, you get #"63.89 g"# of chloride anions, #"Cl"^(-)#. This implies that your sample contains
Now, in order to find the mass by volume percent concentration of chloride anions in the resulting solution, you must determine the mass of chloride anions present in #"100 mL"# of this solution. Since you know that #"500 mL"# of solution contain #"0.3469 g"# of chloride anions, you can say that #"100 mL"# of solution will contain
Therefore, you can say that the mass by volume percent concentration of chloride anions will be
I'll leave the answer rounded to two sig figs, but keep in mind that you have one significant figure for the volume of the solution. #color(white)(.)# Alternatively, you can start by calculating the number of moles of calcium chloride present in your sample
To find the molarity of this solution, calculate the number of moles of calcium chloride present in #"1 L" = 10^3# #"mL"# of solution by using the fact that you have #0.004893# moles present in #"500 mL"# of solution.
You can thus say your solution has
Since every mole of calcium chloride delivers #2# moles of chloride anions to the solution, you can say that you have
This implies that #"100 mL"# of this solution will contain
Finally, to convert this to grams, use the molar mass of elemental chlorine
Once again, you have
In reference to the explanation you provided, you have
because you have #"1 L" = 10^3# #"mL"#. However, this solution does not contain #"0.341 g"# of chloride anions in #"1 L"#. Using
you have
so
This is how many moles of chloride anions you have in #"500 mL"# of solution. Consequently, #"100 mL"# of solution will contain
So once again, you have #"0.06938 g"# of chloride anions in #"100 mL"# of solution, the equivalent of #"0.069% m/v"#. |
When 5.0 g CaCl2 is dissolved in enough water to make a 0.500 L solution What is the molarity of ions in solution?
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