Solution Chemistry Dilutions

Something to think about… What is a solution? Define polarity. What part of a water molecule has positive dipole moment? Negative dipole moment? What happens if we add NaCl to water? – There’s intermolecular forces acting on both molecules that allows for a homogenous mixture to form

Definitions Compare concentrated vs dilute? – Which of the two has more liquid than solid? – Which of the two has more solid than liquid? Compare saturated vs unsaturated? – Which one means that if you add more solute, nothing will happen? – Which one means that if you add more solute, a reaction will still happen? What is a supersaturated solution? – When a solution contains more solute than it would under normal conditions (pressure, temper, etc.)

Definitions Compare solute vs solvent? – What is a universal solvent? – Solvent: Used to to dissolve a solute – Solute: A solute is a solid If you were trying to measure the concentration of something, what would you need to figure it out?

Concentration What words could you use to qualitatively describe a solution’s concentration? Now practice quantitative: – For the solubility lab you did 2 units ago, we had to make 0.10M solutions of several compounds. If the other Chemistry Teachers and I made 25mL of the following solutions, how much mass of the solid compound did we need to measure out and mix with the water? Ammonium Nitrate Potassium Sulfate

For the solubility lab in Unit 3, 0.10M solutions of several compounds were made. Determine the mass of solid a.Ammonium Nitrate b.Potassium Sulfate that was needed to make 25mL of each solution. Molarity Practice

Practice The Lead (II) nitrate in the lab was not quite concentrated enough to work. If I took 15mL of the solution (theoretical: 0.10M) and boiled off all of the water and ended up with 0.094g of lead (II) nitrate, what was the actual concentration of the lead (II) nitrate?

Stock Solutions In the lab, we purchase and store chemicals that are prepared in a concentrated form – Stock solutions Before we do a lab, you use the stock solution and add a certain amount of deionized water to it to obtain the desired molarity of the solution – 12 M HCl is the stock solution, but we need 2.0 M HCl for a lab. – Add water to some 12 M HCl until we reach 2.0 M

Dilution Def.- the process of adding more solvent to a solution Only water is added to the dilution! Amount of solute never changes throughout the dilution There are 12 mol HCl in one liter of 12 M HCl and there will always be 12 moles of HCl even when you dilute it…just adding more water! Moles of solute 1 = Moles of solute 2

Math in Dilutions Then this goes down If this goes up

Math in Dilutions Moles of solute 1 = Moles of solute 2 Molarity 1 x Volume 1 = Moles of solute 1 Molarity 2 x Volume 2 = Moles of solute 2 SO… Molarity 1 x Volume 1 = Molarity 2 x Volume 2 M 1 x V 1 = M 2 x V 2

Example 1 You are helping to set up a lab that calls for 6.0L of 2.0M HCl and the storage room only has bottles of 12M HCl. How much 12M HCl will be required to make 6.0L of 2.0M HCl? Explain the process of making this solution.

Example 2 What volume of water is needed to prepare 500.0mL of a 0.250M Ca(NO 3 ) 2 solution from a 5.00M Ca(NO 3 ) 2 solution?

Example 3 If you combine 50.0ml of.125M solution of sodium phosphate with 75.0ml of 0.100M solution of calcium chloride, what is the mass of solid formed? – What is the limiting reagent? – How many moles of excess reagent remain? – What is the new concentration of excess reagent? – What is the concentration of sodium chloride?

Example 4 (Solutions pre-lab) Same problem, but different numerical values If you combine 10.0 mL of M solution of Calcium chloride with 15.0mL of 0.500M solution of Sodium carbonate,What is the limiting reagent? – What is the limiting reagent? – What is the mass of solid formed? – How many moles of excess reagent remain? – What is the new concentration of excess reagent? – What is the concentration of sodium chloride?

Example 5 If you combine 130.0ml of 0.250M solution of Sodium carbonate with 120.0ml of 0.200M solution of Lead nitrate, – What is the limiting reagent? – What is the mass of solid formed? – How many moles of excess reagent remain? – What is the new concentration of excess reagent? – What is the concentration of Sodium nitrate?

Molarity & Stoichiometry If 150.0mL of 2.66 M Hydrochloric acid is reacted with a large sheet of aluminum, how many mL of 3.00 M AlCl3 is produced? Solution: – Review of Stoichiometry - using Molarity Review of Stoichiometry - using Molarity

– = amount dispensed

Buret Hints and Rules Write down the initial volume! Burets start counting from the TOP not the bottom Sig Figs- measuring to nearest 0.01mL Be careful not to pull off the tip of the buret (tap) Do not jam the flask into the tip of the buret, it will break Make sure the tap is closed when filling with liquid Don’t need to fill exactly to top, just make sure you note the initial volume

Buret Hints and Rules Use a piece of paper for contrast to read the buret Titrate one person at a time so that everyone knows how to do it- if you are in charge of the tap, you are ALSO in charge of watching the volume change 2 groups can share 2 burets When finished, empty the buret, take the tap off and rinse it with water, then bring it back up front