6.2 The pH Scale and Indicators April 30th, 2015

Prayer for the dayGod our Father, you see us, your children, growing up in an unsteady and confusing world: Show us that your ways give more life than the ways of the world, and that following you is better than chasing after selfish goals. Help us to take failure, not as a measure of our worth or of our abilities, but as a chance for a new start. Give us strength to hold our faith in you, and to keep alive our joy in your creation; through Jesus Christ our Lord. Amen.

Learning GoalsWhat is pH?

How do I determine the pH of a solution?

What is a Neutralization Reaction? How do I know one has taken place?

& Possibly…..

What is acid precipitation and what does this have to do with me?

The pH ScaleA scale that typically ranges from 0 to 14, which is used to

classify a solution as acidic, basic, or neutral.

Suggested in 1990 by the Danish chemist named Søren Sørenson……..

Each step up the pH scale you go, the concentration of hydrogen ions goes up 10 times.

For example; a solution that is pH 4 has a hydrogen ion concentration that is 19 times greater than something with a pH 5.

Acidic Solution pH of less than (<) 7

This means there are more HYDROGEN ions in the solution than there are hydroxide ions.

The lower the pH, the more acidic the solution

So, a Lemon at pH 2 is more acidic than milk at pH6

Basic SolutionOn the other end of the scale, bases have pH values higher

than (>) 7

This means there are many more HYDROXIDE ions in the solution than hydrogen.

The higher the pH, the more basic the solution is

So, oven cleaner at pH 13 is more basic than eggs at pH 8

He’s like, so basic…

pH Scale

Neutral SolutionspH = 7

A solution that is neither acidic nor basic is neutral, and falls in the middle of the pH scale at 7

This means that there is an equal number of hydrogen ions present as hydroxide

Water

Determining the pH of a Solution There are several methods that can be used to

help us determine the pH of a solution.

1. pH Meter

2. Litmus Paper

3. Universal Indicator and pH Paper

pH Meter Aka a pH probe.

Uses electrical properties of the solution to determine pH

By connecting the probe to a computer, changes of pH can be analyzed in real time

Litmus Paper

This is a type of “indicator”; a chemical that is added in small amounts to a solution to visibly SHOW you the acidity or the basicity of a solution by changing colour at a particular pH or range of pH values

Litmus solution is often dried onto thin strips; comes in red or blue

Blue litmus paper turns red in an acid

Red litmus paper turns blue in base

In a neutral solution, neither type of litmus changes colour

Only using litmus isn’t sufficient to precisely determine the pH

Universal Indicator and pH PaperTo be more accurate, several indicators that cover the entire

pH range from 0-14 need to be used

Universal indicator is a mixture of different indicators that produce a different colour at different pH values.

pH paper is prepared by soaking strips of paper in universal indicator and allowing it to dry. When you drop a solution on it, you can compare the colour change to a colour chart to determine the pH

Acid-Base NeutralizationWhen an acid and a base are mixed, they react and can

neutralize each other.

Neutralization is the reaction of an acid and a base to produce a salt and water.

Hydrochloric acid + sodium hydroxide

HCl (aq) + NaOH (aq) H2O (l) + NaCl (aq)

HCl (aq) + NaOH (aq) H2O (l) + NaCl (aq)

Double Displacement Reaction

HCl (aq) + NaOH (aq) HOH (l) + NaCl (aq)

Remember:Any ionic compound that is neither an

acid or a base can be called a salt

So in neutralization reactions, you will ALWAYS get some sort of salt and water as the products.

Practice These, k? Don’t forget to balance the equations! H2CO3 and Sr(OH)2

Calcium hydroxide + Phosphoric acid

H2CO3 + Sr(OH)2 2 H2O + SrCO3

CaOH2 + H3PO4 H2O + Ca3(PO4)23 2 6

ConsolidationAcids have a pH of less than 7

Bases have a pH of more than 7

Neutral solutions have a pH of 7

A Neutralization reaction produces a salt and water; everytime