Titrations

Acid-base indicators are… Compounds whose color is sensitive to pH. Either weak acids or weak bases. pH paper is a universal indicator. It is made by soaking the paper in several different indicators.

Phenolphthalein An indicator that changes color from clear in acid to pink in base (pH 8-10). This is the indicator that we will use in the lab during titrations.

Titrations The controlled addition and measurement of the amount of a solution of known concentration (NaOH) required to react completely with a measured amount of a solution of unknown concentration (HCl). Neutralization: A + B  Salt + H 2 O The point of neutralization is the endpoint = change in color of indicator

Good color!Too much base!

Drill #105/7, 5/8/14 Fill in the following table. Need to use your scientific calculator.

Solutions[H + ]pH[OH - ]pOH 1.0 × M HClO M HCl M KOH 6.00 × HBr 0.20 M NaOH H 2 SO 4 1.0×10 -3 M 1.0 × M × M 1.0 × M × M 1 × M × M1.67 × M × M 2.0 × M × M 1.67 × M

Solutions[H + ]pH[OH - ]pOH 1.0 × M HClO M HCl M KOH 6.00 × HBr 0.20 M NaOH H 2 SO 4 1.0×10 -3 M 1.0 × M × M 1.0 × M × M 1 × M × M1.67 × M × M 2.0 × M × M 1.67 × M

Agenda Go over Titration Curve Graph Acid and Base strength Titration Calculation Problems Titration Lab

Homework Titration Problems Titration Lab

Titration Curve for strong acid & strong base

Equivalence Point The point at which the two solutions used in a titration are present in equal amounts Amount of acid in moles = Amount of base in moles This can be found using an indicator – in a perfect world, the endpoint (point at which the indicator changes color) would be the same. *Note: this is not the same volume or the same concentration, just the same MOLES

Equivalence Point Strong acid + strong base = equivalence point at pH of 7 Strong acid + weak base = equivalence point at pH of <7 Weak acid + strong base = equivalence point at pH of >7

How to solve titration problems: 1.Write the balanced neutralization equation 2.Solve for moles of given (using molarity and volume) 3.Convert from moles of given to moles of unknown using mole ratio 4.Use moles of unknown to solve for molarity or volume. NOTE: If moles are equivalent (coefficients) then: M A V A =M B V B

Assignment Titration Problems

Titration Lab Place 5 ml of HCl in Erlenmeyer flask Add 2 drops of phenolphthalein indicator to the flask Take an initial volume buret reading Place sheet of white paper under flask during titration Titrate with.50 M NaOH until you get a pale pink color that stays pink for about 10 secs Make sure you carefully swirl flask after each titration If you think you have reached the endpoint, record final volume of NaOH.

Sample Titration Prob Record calculations on half sheet of paper.

Drill #185/24 & 28/13 A student titrates a 20 ml sample of a solution of HBr with unknown molarity. The titration requires ml of a M solution of NaOH. What is the molarity of the HBr solution? Answer: M A 35 ml sample of ammonium hydroxide is titrated to the end point with ml of a M sulfuric acid. What is the molarity of the ammonium hydroxide? Answer: 1.26 M

Agenda Go over Review Packet Test

Drill #16 5/22 & 23/13 Calculate the pH for the following solutions and indicate whether the solution is acidic (A), basic (B), or neutral (N). 1.[H + ] = 1 x M 2.[OH - ] = 1 x M 3.[OH - ] = 1 x M 4.[H + ] = 1 x M What are the [OH - ] for solutions with the following ph values?

Drill #16 5/22 & 23/13 Calculate the pH for the following solutions and indicate whether the solution is acidic (A), basic (B), or neutral (N). 1.[H + ] = 1 x M – 2, A 2.[OH - ] = 1 x M – 12, B 3.[OH - ] = 1 x M – 6, A 4.[H + ] = 1 x M – 6, A What are the [OH - ] for solutions with the following ph values? 5. pH = 4.0; pOH = 10; [OH - ] = 1 x M 6. pH = 8.0; pOH = 6; [OH - ] = 1 x M

Drill #17 5/22 & 23/13 Write the names for the following acids and bases: a) KOH b)HF c)H 2 SO 3 d)Fe(OH) 2 e)HCN Write the formulas for the following acids: a) phosphorous acid b) hydrobromic acid c) carbonic acid

Drill #17 5/22 & 23/13 Write the names for the following acids and bases: a) KOH - potassium hydroxide b)HF - hydrofluoric acid c)H 2 SO 3 - sulfurous acid d)Fe(OH) 2 – iron (II) hydroxide e)HCN - hydrocyanic acid or cyanic acid Write the formulas for the following acids: a) phosphorous acid - H 3 PO 3 b) hydrobromic acid - HBr c) carbonic acid - H 2 CO 3

Agenda Titration Calculations Titration Lab (4B – postponed until next wk) Announcements Turn in Naming Bases and Crossword Puzzle Test next class.

If we know the molarity and the volume of acid used, then can we calculate the amount of moles of acid? How? Mol A = M A V A

Worksheet!

Green workbook, pg

Test Topics Properties of acids, bases, and salts Bronsted-Lowry definition of acids/bases Amphoteric substance Neutralization reaction – must be balanced Purpose of calculating an Acid or Base dissociation constant Naming acids Equations for pH, pOH, [H + ], and [OH - ] Titration calculations

Objective SWBAT calculate molarity of acid using data from titration.