The Chemistry of Acids and Bases

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You should only use a small portion of the paper. You can use one piece of paper for several tests.

Slide 61

pH paper

Slide 62

pH meter

Tests the voltage of the electrolyte

Converts the voltage to pH

Very cheap, accurate

Must be calibrated with a buffer solution

Slide 63

pH indicators

Indicators are dyes that can be added that will change color in the presence of an acid or base.

Some indicators only work in a specific range of pH

Once the drops are added, the sample is ruined

Some dyes are natural, like radish skin or red cabbage

Slide 64

ACID-BASE REACTIONS Titrations

H2C2O4(aq) + 2 NaOH(aq) --->

acid base

Na2C2O4(aq) + 2 H2O(liq)

Carry out this reaction using a TITRATION.

Slide 65

Setup for titrating an acid with a base

Slide 66

Titration

1. Add solution from the buret.

2. Reagent (base) reacts with compound (acid) in solution in the flask.

Indicator shows when exact stoichiometric reaction has occurred. (Acid = Base)

This is called NEUTRALIZATION.

Slide 67

35.62 mL of NaOH is neutralized with 25.2 mL of 0.0998 M HCl by titration to an equivalence point. What is the concentration of the NaOH?

LAB PROBLEM #1: Standardize a solution of NaOH — i.e., accurately determine its concentration.

Slide 68

PROBLEM: You have 50.0 mL of 3.0 M NaOH and you want 0.50 M NaOH. What do you do?

Add water to the 3.0 M solution to lower its concentration to 0.50 M

Dilute the solution!

Slide 69

PROBLEM: You have 50.0 mL of 3.0 M NaOH and you want 0.50 M NaOH. What do you do?

But how much water

do we add?

Slide 70

PROBLEM: You have 50.0 mL of 3.0 M NaOH and you want 0.50 M NaOH. What do you do?

How much water is added?

The important point is that --->

Slide 71

PROBLEM: You have 50.0 mL of 3.0 M NaOH and you want 0.50 M NaOH. What do you do?

Amount of NaOH in original solution =

M • V =

(3.0 mol/L)(0.050 L) = 0.5 M NaOH X V