pH Scale

How do we measure the strength of acids and bases? pH: stands for the strength or concentration of hydrogen ions (H1+) in a solution.

pH Scale pH 7 is neutral. (Water) pH 1 is a very acidic. pH 13 is a very basic. pH 4 is 10 times stronger than pH 5 pH 3 is 100 times stronger than pH 5 Very Acidic Weakly Acidic Weakly Basic Very Basic Neutral

Very Acidic Very Basic Weakly Acidic Weakly Basic Neutral H+ H+ OH– Detergents Drain Cleaner Very Acidic Weakly Acidic Weakly Basic Very Basic Neutral Blood Ant Bites Stomach Acid Acid Rain H+ H+ OH– OH– H+ H+ OH– H+ H+ OH– H+ OH– OH– H+ OH– H+ H+ OH– OH– H+ OH– H+ OH– OH–

Many solutions of acids or bases are clear and colourless We use indicators to distinguish them from water, and tell whether a substance is acidic, basic or neutral There are many, many indicators, and each one has a different colour in acidic solutions versus basic solutions

Some Common indicators are: 1) Phenolphthalein drops (acid/neutral is clear, base is pink)

Some Common indicators are: Litmus paper – red litmus turns blue in base – Blue litmus turns red in acid

Some Common indicators are: 3) Universal pH paper – range of colours

Some Common indicators are: 4) Cabbage Juice – range of colours

Some Common indicators are: 5) pH meter – tells you exact pH

*When you’ve achieved the transition colours, show Mrs. Innes* Thymol blue Activity Instructions Put on your goggles and grab a test tube holder Get 3 test tubes, label HCl & NaOH & mixture Get 2 pipettes, label HCl & NaOH Get ½ a test tube of HCl and NaOH into appropriate test tubes. Add 2cm of HCl to mixture test tube. Add 3 drops of thymol blue to the mixture test tube Use only the appropriate test tube pipettes to add acid or base to get all the colours of the scale. *When you’ve achieved the transition colours, show Mrs. Innes*

The Importance of pH 1. The pH of environment effects plants and animals. ex. hydrangea flowers, frog or Fish survival Netural soils = white or pale petals Acidic soils = blue petals Basic soils = purple or pink petals.

2. The pH of your body affects your health 2. The pH of your body affects your health. If you are too acidic, yeast and bad bacteria can grow. Normal blood has a pH of 7.4, if pH falls below 6.8 or above 7.8 it is considered fatal.

3. Cosmetic/hair products with different pH’s have different effects 3. Cosmetic/hair products with different pH’s have different effects. Acidic ones make hair shiny and flexible. Basic ones make hair soft and straight.

Cabbage Lab