1. UNIT 1 ACIDS, ALKALIS & CHEMICAL REACTIONS Lesson 1 - Introduction

2. Aims of the Lesson I know what an acid is and how I can detect it.
I know what an alkali is and how I can detect it.
I know that substances which are not acidic or alkaline are neutral.

3. ACIDS & ALKALIS
We use many acids and alkalis everyday, but some can be very dangerous and cause damage to our skin.
We must be careful when handling these chemicals.

4. ACID OR ALKALI?
We can add chemicals called INDICATORS to a substance to find out if it is acid or alkali.
Two indicators that we will use are universal indicator, which is a liquid, and pH paper.
Indicators change colour when added to a substance.
TODAY WE WILL USE UNIVERSAL INDICATOR NOT pH PAPER.
UNIVERSAL INDICATOR
pH PAPER

5. UNIVERSAL INDICATOR Universal indicator solution will turn:
Yellow /Orange/Red with acids
Blue/Purple with alkalis
Green with neutral substances (neither acid nor alkali)

6. pH SCALE
We can compare the colour of the universal indicator to the pH scale, using a colour chart to find out how strong or weak an acid or alkali is.
NEUTRAL
STRONG ACID WEAK ACID WEAK ALKALI STRONG ALKALI pH

7. MEASURING pH with U.I. 1. Collect a test tube and a test tube rack
2. Collect universal indicator (U.I.) and a dropper
3. Add approx 5 cm3 of a sample to one test tube then a few drops of U.I. Shake (carefully)
4. Repeat for each sample and record results. (COMPLETE ONE AT A TIME.)

8. ACID or ALKALI or NEUTRAL
MEASURING pH
Copy this table in to your jotter and complete as you carry out the experiment:
SOLUTION
Colour pH
ACID or ALKALI or NEUTRAL
Example
RED 3
Acid
Hydrochloric Acid
Sodium Hydroxide
Salt solution
Sugar solution
Baking Soda sol.
Lemonade
Irn bru
Washing up liquid
Vinegar
Water

9. Copy and complete this SUMMARY:
Acids have pH values of _____. They turn universal indicator solution ________________.
Alkalis have pH values of _____. They turn universal indicator solution___________.
Neutral solutions have a pH value of ___. They turn universal indicator solution ______.
0-6
yellow / orange / red
8-14
blue / purple 7
green

10. Check Test
What two methods can you use to find out if a substance is an acid or an alkali?
The pH scale goes from What would the normal range be for:
a) an acid? b) an alkali?
3) Can you think of any limitations that the pH paper might have?