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Molarity

Molarity. What is molarity?. Molarity is a unit of concentration. This is probably the MOST IMPORTANT unit of concentration that we work with in chemistry. Definition and Formula. Molarity (M), the amount of solute dissolved in a given amount of solution (not a given amount of solvent)

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Molarity

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  1. Molarity

  2. What is molarity? • Molarity is a unit of concentration. This is probably the MOST IMPORTANT unit of concentration that we work with in chemistry.

  3. Definition and Formula • Molarity (M), the amount of solute dissolved in a given amount of solution (not a given amount of solvent) • M = moles solute/ liters of solution

  4. How to solve molarity problems

  5. Example #1: Calculate the molarity, M, of a solution prepared by dissolving 12.0 grams of potassium permanganate, KMnO4, in enough water to make 750. ml of solution. Step 1. Are we given grams or moles? Do we need to do any conversions?Step 2. Are we given milliliters or Liters? Do we need to do any conversions?Step 3. What equation are we going to use to solve?

  6. Other kinds of molarity problems

  7. Example #2: Calculate the moles of NaCl needed to prepare 175 ml of 0.500 M saline solution.Step 1. Are there grams or moles in this question?Step 2. Are we given milliliters or Liters? Do we need to convert?Step 3. Which equation do we use?

  8. Example #3: Calculate the liters needed to prepare a 2.5 M sodium hydroxide solution containing 31.52 moles of NaOH.Step 1. Are there grams or moles in this question? Do we need to convert?Step 2. Are we given milliliters or Liters? Step 3. Which equation do we use?

  9. Kool-Aid Lab • Safety Do NOT use any of the lab equipment to measure liquid or solids. Food Safe materials have been provided for you so that you may taste the koolaid at the end of the lab. • Groups of 3-4 students each (will be assigned to a lab station) • Must complete pre-lab and show Ms. Kristoff before going to lab station and beginning lab. • Procedures to note • There are 4 plastic cups and sharpies • Label one cup each: • measure • #1 (0.1M) • #2 (0.4M) • #3 (0.7M) • When measuring Koolaid powder be sure to “zero” out the balance first! • Record all observations in data table. • Make sure to dispose of extra koolaid down the drain, recycle cups, and wipe lab benches when completed. • Anything not completed at end of class is homework due Tuesday next week.

  10. Checks for Understanding • Answer the following questions yes/no with red and green cards. • Green = yes, Red = no • You dropped the plastic spoon on the floor and need something to stir your koolaid. Can you open the drawer and grab a glass stir rod to use instead? • You must show Ms. Kristoff your completed pre-lab before going to your designated lab station. • You must clean your lab-bench after recording your data on the data table.

  11. Exit Ticket On the sticky note at your desk complete the following calculations. When finished, go to the back of the room and place the sticky note on either the Green, Yellow, or Red Circle to indicate your level of understanding/confidence in calculating molarity problems. 1.  A solution has a volume of 2.5 L and contains 7.0 moles of NaCl.  Determine the molarity. 2. How many grams of KCl are in 0.335 L of a 0.425 M solution?

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