AQUEOUS SOLUTIONS

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AQUEOUS SOLUTIONS . Mole = Amount of a substance that has a mass in gramsnumerically equivalent to its molecular weight in Daltons.For example: To determine a mole of sucrose (C12H22O11).Calculate molecular weight:C = 12 Da 12 Da x 12 = 144 DaH = 1 Da 1 Da x 22 =

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AQUEOUS SOLUTIONS

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1. AQUEOUS SOLUTIONS Solute Concentration Molecular Weight = Sum of weight of all atoms in a molecule (expressed in Daltons). For example: Determine a mole of CH3COOH CH3COOH 2 C 2 x 12 Da = 24 4 H 4 x 1 Da = 4 2 O 2 x 16 Da = 32 --------------------- M.W. Da = 60 g/mol

2. AQUEOUS SOLUTIONS Mole = Amount of a substance that has a mass in grams numerically equivalent to its molecular weight in Daltons. For example: To determine a mole of sucrose (C12H22O11). Calculate molecular weight: C = 12 Da 12 Da x 12 = 144 Da H = 1 Da 1 Da x 22 = 22 Da O = 16 Da 16 Da x 11 = 176 Da 342 Da Express it in grams (342 g).

3. AQUEOUS SOLUTIONS Molarity = Number of moles of solute per liter of solution. For example: To obtain 1 M sucrose solution, weigh out 342 g and add water up to 1L. Advantage of measuring in moles: 1. Rescales weighing single molecules in Daltons to grams, which is more practical for laboratory use. 2. A mole of one substance has the same number of molecules as a mole of any other substance (6.02 x 1023; Avogadro’s number). 3. Allows one to combine substances in fixed ratios of molecules

4. AQUEOUS SOLUTIONS For example: How much CH3COOH do you need to make 1 liter of a 2 M solution of CH3COOH? Ask yourself these questions: How many grams of this substance are in 1 mole of CH3COOH? 2. How many liters are you trying to prepare? 3. What is the ultimate concentration you are trying to prepare (M)?

5. AQUEOUS SOLUTIONS Answer: 60 grams/mole x 1 liter x 2 moles/liter = 120 g of CH3COOH is needed to prepare a 2 M solution.

6. AQUEOUS SOLUTIONS For Example: How much CaCl2 do you need to make 750 ml of a 1.5 M CaCl2 solution? How many grams/mole? 110 g/mol How many liters? .750 L What is M? 1.5 M

7. AQUEOUS SOLUTIONS Answer: 110 g/mole x .750 L x 1.5 moles/liter = 123 g You will need 123g of CaCl2

8. AQUEOUS SOLUTIONS For Example: You want to make a 10 M C6H12O6 solution. If you have 900 grams of C6H12O6, how much can you make? How many grams/mole? 180 g/mol What is the M desired? 10 M How many grams total do you have to work with? 900 grams

9. AQUEOUS SOLUTIONS Answer: You can make 0.5 L of a 10 M C6H12O6 solution

10. AQUEOUS SOLUTIONS What if the question would have asked for a 2.5 M C6H12O6 solution? What about a 4 M C6H12O6 solution?

11. AQUEOUS SOLUTIONS Answer: 5 moles / 2.5 moles/liter = 2 L 5 moles / 4 moles/liter = 1.25 L

12. AQUEOUS SOLUTIONS For Example: What is the molar concentration of a NaOH solution where you have been given 60 grams of NaOH and ask to prepare a final volume of 3 liters? What is the amount of grams/mole? = 40 g/mole How many grams do you have? 60 grams What is your desired volume? 3 L

13. AQUEOUS SOLUTIONS Answer: 60 grams / 40 grams/mole = 1.5 mole 1.5 moles / 3 liters = 0.5 moles/liter The molar concentration is 0.5 M.

14. Acids, Bases and pH Dissociation of Water Molecules (pH) Occasionally, the hydrogen atom that is shared in a hydrogen bond between two water molecules, shifts from the oxygen atom to which it is covalently bonded to the unshared orbitals of the oxygen atom to which it is hydrogen bonded.

15. Figure 3.9 The pH of some aqueous solutions

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