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# Self-Ionization of Water and the pH Scale

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Author: carolyn fruin
##### Description:

Learning Targets:

• I can write the equation for the self-ionization of water.
• I can write the equilibrium expression for water.
• I know that the value of Kw is 1 x 10-14.
• I can explain that every aqueous solution contain some H+ and some OH-.
• I can use Kw to calculate for the equilibrium concentrations of [H+]  or  [OH-].
• I know the various pHs of common household materials.
(more)

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Tutorial

## Computer Tutorial - pH Scale

This video illustrates how water reacts with itself to form ions. It also determines the equilibrium constant for water, Kw. CLICK HERE to begin. Once you have watched the video, answer the questions listed below.

1. What are some common items and their corresponding pHs?
2. How are pH and pOH related?
3. Describe how the strength of an acid is related to its concentration.
4. As you complete each of the example problems, record your correct answers.

Source: W. W. Norton & Company

## The Concept of pH

Covers basic self-ionization of water, the pH scale and pH calculations.

## pH Scale Basics

The pH of a solution

•is used to indicate the acidity of a solution
•has values that usually range from 0 to 14
•is acidic when the values are less than 7
•is neutral with a pH of 7
•is basic when the values are greater than 7

The pH of solutions is determined by using
• a pH meter
• pH paper
• indicators that have specific colors at different pH values

## Computer Tutorial - Self Ionization of Water

This video illustrates how water reacts with itself to form ions. It also determines the equilibrium constant for water, Kw.  CLICK HERE to begin. Once you have watched the video, answer the questions listed below.

1. Write the chemical reaction between two water molecules.
2. What is the equilibrium expression for this reaction?
3. How was it determined that Kw = 1 x 10-14?

Source: W. W. Norton & Company

## What is Kw?

A description of how Kw is developed using the Keq of water and how it was determined to be 1 E -14.