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Molarity & Dilutions

Molarity & Dilutions. A Substance Inside a Solution. Different solutes can dissolve in a variety of solvents, most often water A dilute solution is one that contains a small amount of solute A concentrated solution contains a large amount of solute

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Molarity & Dilutions

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  1. Molarity&Dilutions

  2. A Substance Inside a Solution Different solutes can dissolve in a variety of solvents, most often water A dilute solution is one that contains a small amount of solute A concentrated solution contains a large amount of solute Much attention is given to how one quantifies the amount of solute dissolved

  3. Concentration of Solutions In solution chemistry, molarity is used to describe how much solute was dissolved in the solvent Concentration is the relationship between the dissolved substance and the solution Units are called “Molar” (M) MOLARITY = Moles of Solute mol OR Volume of Solution (Liters) L

  4. Molarity (M) • A 1M solution is equal to 1 mol of solute in 1L of solution • Volumetric Flask • Glassware used to measure precise volumes • The solute is put into a volumetric flask • Water is added to make a 1L solution

  5. Calculating Molarity • Convert the mass of a given substance into moles • If necessary, convert volume into liters • Remember: 1,000mL = 1L • Plug into the equation: MOLARITY = Moles of Solute mol OR Volume of Solution (Liters) L

  6. Molarity Example #1 • What is the molarity of a 1.5L solution containing 18.3g of sodium chloride? • We need to change 18.3g NaCl into moles of NaCl 18.3g NaCl x 1 mol NaCl = 58.44g NaCl .31 mol NaCl Molarity = Moles of Solute = .31 mol NaCl = .207 M Volume of the Solution (L) 1.5 L

  7. Molarity Example #2 • Calculate the molarity of a magnesium oxide solution containing 12.4g of magnesium oxide and has a total volume of 750mL. • First we need to convert grams to moles and mL to Liters! • 12.4g MgO X 1 mol MgO= .307 mol MgO • 40.30g MgO 750mL x 1 L = .750L 1000mL .307 mol MgO Molarity = mols of solute = Volume of solution (L) = .409 M .750L

  8. Performing Dilutions A solution may be too concentrated for a certain chemical reaction A dilution (adding more solvent) can be done to decrease the ratio of moles of solute to liters of solvent by the following equation: The moles of solute are constant while only the amount of solvent changes

  9. Making a Dilute Solution

  10. Dilution Example #1 How many milliliters of solution of 4.00M KI are needed to prepare 250 mL of 0.760M KI?

  11. Dilution Example #2 What volume of 12.00M Sulfuric Acid is required to prepare 1 Liter of 0.400M Sulfuric Acid?

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