Universal Indicator And The Ph Scale

Universal Indicator and the pH scale

LOs •Understand what universal indicator is. •Understand the pH scale.

Answer these questions on the last lesson in the back of your book: 2. What colour did our cabbage indicator go in acid, alkali and neutral? 3. Red cabbage turns blue if we cook it in water. What could we add to keep it red?

What we did last time…

Universal indicator A special indicator that shows different colours for different strengths of acids and alkalis. stronger acid

strong acid

stronger alkali

weak weak acid neutral alkali

strong alkali

The pH scale stronger acid

stronger alkali

1 2 3 4 5 6 7 8 9 10 11 12 13 14 strong acid

weak weak acid neutral alkali

strong alkali

Homework Tomorrow we will have a quick test on the pH scale. Things to know: • The pH value of a neutral substance • The range of pH’s of an acid • The range of pH’s of an alkali • Whether an acid alkali is stronger / weaker than another one by it’s pH value

True or False

pH = 14

True or False

pH = 7

True or False

pH = 14

True or False

Weak Acid

True or False Universal indicator and litmus are the same thing.

True or False Universal indicator shows us: • Whether a substance is an acid or alkali and, • How strong the acid or alkali is.

True or False Universal indicator goes purple in a strong acid.

True or False Neutral substances turn universal indicator green

True or False Weak alkalis turn universal indicator blue

True or False Weak acids turn universal indicator red.