1. Solutions - Quantitatively

2. Solutions Mixture of at least two components Mixture of at least two components Solute Solute Solvent Solvent Components can be any phase Components can be any phase Usually liquid solvent, but can be solid or gas Usually liquid solvent, but can be solid or gas Examples ? Examples ?

3. Quantifying Solution Components Concentration Concentration Ratio of solute to solvent present Ratio of solute to solvent present Qualitative Descriptors: Concentrated, Dilute, Saturated, Unsaturated Qualitative Descriptors: Concentrated, Dilute, Saturated, Unsaturated Ways to measure Ways to measure Concentration Concentration Molarity Molarity Molality Molality % by mass % by mass Mole Fraction Mole Fraction

4. Molarity Symbol = (M) or (M) Symbol = (M) or (M) M = moles of solute M = moles of solute Liter of solution Liter of solution How to make a 1.0 M solution of NaCl: How to make a 1.0 M solution of NaCl: - Measure out 1.0 mole of NaCl, pour into a volumetric flask - Add enough water to make exactly 1.0 L of solution

5. Practice Calculation Calculate the molarity of a solution that is made of 1.56 grams of gaseous HCl dissolved in enough water to make 26.8 mL of solution. Calculate the molarity of a solution that is made of 1.56 grams of gaseous HCl dissolved in enough water to make 26.8 mL of solution. Step 1: Step 1: Step 2: Step 2: Step 3: Step 3: Calculate the number of moles of HCl Convert the volume to Liters Divide the moles of solution by the Liters of solution Answer = 1.60 M HCl

6. More Practice… What is the molarity of a solution prepared by dissolving 11.5 g of NaOH in enough water to make 1.50 L sol’n? What is the molarity of a solution prepared by dissolving 11.5 g of NaOH in enough water to make 1.50 L sol’n? If I want to make 1.00 L of a 0.200 M solution of K 2 Cr 2 O 7, how much solid potassium dichromate do I need? If I want to make 1.00 L of a 0.200 M solution of K 2 Cr 2 O 7, how much solid potassium dichromate do I need? How many moles of CuCl 2 are in 250 mL of 3.0 M sol’n? How many moles of CuCl 2 are in 250 mL of 3.0 M sol’n? What are the concentrations of all ions present in a 0.50 molar solution of Co(NO 3 ) 2 ? What are the concentrations of all ions present in a 0.50 molar solution of Co(NO 3 ) 2 ? Answer = 0.192 M Answer = 58.8 g K 2 Cr 2 O 7 Answer = 0.75 moles Answer = [Co +2 ] = 0.50 M [NO 3 -1 ] = 1.0 M

7. Dilution Calculations Start with Concentrated Stock Solution of known concentration Start with Concentrated Stock Solution of known concentration Add water to make diluted solution of specific desired concentration Add water to make diluted solution of specific desired concentration Example: Prepare 500. mL of 1.0 M HCl from 12.0 M stock. Example: Prepare 500. mL of 1.0 M HCl from 12.0 M stock. Step 1: Step 1: Step 2: Step 2: Step 3: Step 3: Determine moles of HCl needed in final solution. Determine volume of stock with that number of moles HCl. Add enough water to stock to make volume needed.

8. Example: Prepare 500. mL of 1.0 M HCl from 12.0 M stock. Step 1: Step 1: Determine moles of HCl needed in final solution. Step 2: Determine volume of stock with that number of moles HCl. Step 3: Add enough water to stock to make volume needed. 500. mL solution x 1L x 1.0 mole HCl = 0.500 moles HCl 1000 mL 1.0 L sol’n 12.0 mol HCl = 0.500 mol HCl 1.00 L sol’n x L solution X = 0.042 L or 42 mL stock Add 458 mL water to the 42 mL of stock to make exactly 500. mL of 1.0 M HCl. Moles of HCl in stock = Moles of HCl in dilution

9. Stoichiometry of Precipitation Rxns Calculate the mass of solid NaCl that must be added to 1.50 L of a 0.100 M AgNO 3 solution to precipitate all of the Ag + ions in the form of AgCl. 1: Write the balanced net ionic equation. 2: Determine the number of moles of Ag + present. 3: Determine how many moles Cl -1 ions are needed to react all Ag +, and therefore, how many grams NaCl that is. Answer = 8.77 grams NaCl

10. Another example… When sodium sulfate and lead (II) nitrate are mixed, a precipitate forms. Calculate the mass of the precipitate when 1.25 L of 0.0500 M lead (II) nitrate are mixed with 2.00 L of 0.0250 M sodium sulfate. 1: Write the balanced equation, then the net ionic equation. 2: Calculate the moles of each reactant that produces precipitate. Determine which is limiting. 3. Calculate the number of moles of product formed. Convert to grams. Answer = 15.2 grams of PbSO 4

11. Acid/Base Reactions What volume of a 0.100 M HCl solution is needed to neutralize 25.0 mL of 0.350 M NaOH solution? 1: Write the balanced equation, then the net ionic equation. 2: Calculate the moles of each reactant. Determine which is limiting. 3: Calculate moles of reactant needed, then convert to Volume. Answer = 8.75 x 10 -2 L or 87.5 mL 0.100 M HCl

12. Acid/Base Titrations Quantitative Acid/Base Neutralizations Quantitative Acid/Base Neutralizations Used to determine unknown concentration of acid or base. Used to determine unknown concentration of acid or base. Indicator is added so that endpoint/equivalence point of reaction is seen. Indicator is added so that endpoint/equivalence point of reaction is seen.

13. Acid/Base Titrations For calculation of the unknown concentration to be successful, you must : For calculation of the unknown concentration to be successful, you must : Know the exact reaction happening. Know the exact reaction happening. Be able to accurately reach the equivalence point experimentally. Be able to accurately reach the equivalence point experimentally. Be able to determine the exact volume of titrant added to reach the equivalence point. Be able to determine the exact volume of titrant added to reach the equivalence point. M (H+) V (H+) = M (OH-) V (OH-) M (H+) V (H+) = M (OH-) V (OH-)

14. Equivalence Point Phenolphthalein Indicator Before Eq. Pt.At Eq. PtOvertitrated

15. Graphical Analysis of Titration

16. Titration Calculation M (H+) V (H+) = M (OH-) V (OH-) M (H+) V (H+) = M (OH-) V (OH-) A 25.00 mL sample of HCl (aq) requires 24.16 mL of 0.106 M NaOH for complete neutralization. What is the concentration of the original hydrochloric acid solution? A 25.00 mL sample of HCl (aq) requires 24.16 mL of 0.106 M NaOH for complete neutralization. What is the concentration of the original hydrochloric acid solution? Answer = 0.102 M HCl