| 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
With this molality calculator you can quickly calculate the molality - one way of measuring the concentration of a solute in a solution (not to be confused with molarity). Simply type the number of moles of your solute substance and mass of the solvent and the tool will calculate the molality. If you don't know how many moles of a substrate you have, use the advanced mode to calculate it with the use of mass and molar mass of the compound. Are you still unsure what's the molality definition, its units and formula - or simply how to calculate molality step by step? Keep reading and you'll find the answer!
Molality, also called molal concentration, is defined as the amount of substance of solute, divided by the mass of the solvent msolvent: Molality = nsolute / msolvent = msolute / (Wsolute × msolvent) where
The molality unit from the SI system is mol/kg; sometimes, the name molal is used (though it's considered obsolete). Molality plays a significant role in calculating the ionic strength of a solution.
Molarity and molality are similar concepts - both are measures of the concentration of a solution. However, there is one main difference between those terms: molarity is expressed as the amount of substance per unit volume of solution, whereas molality defines the concentration as the amount of substance per unit mass of the solvent.
We've put all the most important differences between those two terms into a short molarity vs. molality table:
To change between molarity and molality, you can use the following relation: M = m × d / (1 + m × W) where
Let's show on the example how to calculate molality:
To compute the molality of a solute, you need to:
The answer is 6 mol/kg. To see how this result is derived, recall that the formula for molality reads molality = moles of solute / mass of solvent in kg. Plugging in moles of solute = 3 and mass of solvent = 0.5 kg, we obtain molality = 3 / 0.5 = 6 mol/kg, as claimed.
The formula that allows us to convert molarity to molality is the following: m = M/( d - M × W) where:
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What is the molality of 150.0 g of nh3 dissolved in a solution that is 1.25 liters the density of the solution is 1.45 g mL?
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