Dilutions

What is a dilution? M1V1 = M2V2 Taking a CONCENTRATED solution and making it LESS concentrated Adding more solvent to decrease the amount of solute in the solution M1V1 = M2V2 Used when 2 solutions are involved Units do not matter but keep the same units throughout the problem !!! Ex. Tea and sweetner

Example 1: Prepare 2.50L of a 0.360M H2SO4 solution from a stock H2SO4 solution of 18.0 M. 50 ml of 18.0 M sulfuric acid

Example 2: A stock solution of KF has a concentration of 1.20M. To what final volume must 100ml of this solution be diluted to produce a 0.45 solution of KF? 0.267L, 267 ml

Example 3: What volume of 17.4 M acetic acid is needed to prepare 1.00 L of 3.00 M acetic acid? How much water would I need to add to 500ml of a 2.4M KCl solution to make a 1.0M solution? 0.172 L or 172 ml

Serial Dilutions A type of dilution The dilution is made through a series of smaller dilutions from a stock or original solution

Acid/Base Titration

Titration Used to determine UNKNOWN concentrations of solutions through a solution of KNOWN concentration. An acidic or basic solution of KNOWN concentration is added to an acidic/basic solution of UNKNOWN concentration. Indicators such as phenolphtalein display a change when all of the acid or base has been neutralized. Several types—we are focusing on acid/base titration Change is usually color. At neutralization, equal number of base and acid is present so don’t want to keep pouring because you will turn it into a basic solutionm.

To the right is the titration using an indicator.

Titration Terminology End Point: point in a titration where a change is observed due to indicator. Equivalence Point: point in a titration where enough base or acid is present to neutralize the acidic or basic solution. We can plot a titration on a graph—titration curve End point—color change with indicator Want to use indicators where end point and equivalence points are roughly the same. Why? So we can tell when neutralization has happened and stop adding base. Some indicators (phenolphtalein) do not change color right at equivalence point—so stop titration when a pink color persists for 10 seconds

Show points on graph and how titration proceeds. Have students draw graphs. **Maybe**

MaVa = MbVb Calculations Where M is the molarity & V is the volume Used to determine final concentration vs original concentration. Solve like you would dilution problems.

Example 1: We have two solutions (H2SO4 and KOH). The KOH solution has a concentration of 0.1500M and takes 42.61ml to titrate 25.0ml of the sulfuric acid solution. What is the concentration of the H2SO4 solution? Work out problem on Elmo. If we know the base concentration and the amount of acid we have—we can calculate the acid’s concentration -pour base into solution until equivalence point and then read buret to tell how much base was needed (amt in volume) to neutralize acid. **describe titration**

Example 2 14.5ml of HNO3 was neutralized in a titration using 12.5ml of Ba(OH)2 with a 1.75x10-2M concentration. What is the concentration of the HNO3 solution? Work out problem on Elmo

Example 3: If 29.96 ml of a solution of Ba(OH)2 requires 16.08 ml of a 2.303M solution of HNO3 for complete titration, what is the molarity of the Ba(OH)2 solution? 0.6180 M Ba(OH)2