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3. Units of Concentration

3. Units of Concentration. Definition. same. unitless. same. Advantages/disadvantages of each (read only; no lecture). Example problems

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3. Units of Concentration

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  1. 3. Units of Concentration Definition same unitless same Chapter 11

  2. Advantages/disadvantages of each (read only; no lecture) Chapter 11

  3. Example problems 1. Determine the molarity of a 0.258 m solution of glucose given that the solution’s density is 1.0173 g ml-1 and that the molar mass of glucose is 180.2 g. • first, write down definitions: molarity is moles solute per litersolution; molality is moles solute per kg solvent; density is mass solution per volume solution we want: moles solute/liter solution • assume some amount of solution to start: in this case 0.258 moles glucose and 1 kg water so we have 0.258 moles solute Chapter 11

  4. get the total volume of the solution - glucose plus water mass sol’n volume sol’n • solve for the molarity Chapter 11

  5. 2. Determine the molality of a 0.500 M solution of acetic acid (molar mass 60.02 g) with a density of 1.0042 g ml-1. • Again, write down the units and their definitions. • Start by assuming 1 L of solution and thus 0.500 moles acetic acid • determine the mass of the solution from the density times the volume • determine the mass of water (in kg) by subtraction (subtract the mass of the acetic acid from the mass of the solution) • solve for the molality Chapter 11

  6. 3. Describe how 1.50 L of a 12.0% KBr solution is made if the solution density is 1.10 g ml-1. In other words, determine the mass of KBr and the mass of water to be mixed together. • Write out the units and their definitions • 1.50 L or 1500 ml of solution are required; determine the total mass of solution required (HOW?). • Of the total mass of solution, how much must be KBr? • Determine the mass of water necessary (HOW?). Chapter 11

  7. total mass solution mass KBr mass water dissolve 198 g KBr in 1452 g water Chapter 11

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