The pH scale and soil testing.

The pH scale.

The pH scale measures how acidic (or how alkaline) a substance is. Most of the substances which you handle in the lab have pH values between t and 14. A substance with pH 1 is very acidic. A substance with pH 14 is very alkaline. A substance with pH7 is neutral.

Soil testing.

When the smart family arrived at their new home, Fred looked at the garden, thought of his father, and shuddered. The garden was huge. His father was a gardening fanatic who did everything just as the book said. That meant lots of work for Fred!

Acids and alkalies.

There are very many different chemicals - so many that it’s impossible to study them all. To make things simpler, scientists Put chemicals which behave the same way into groups or sets. You Have already met the set of metals. Acids and alkalis are two More of these chemical sets.

You can find out if a substance is an acid, or an alkali, by dissolving it and adding universal indicator. The diagram shows you how to do this.

The indicator's colour changes if acid or alkali is added to it. And so, by matching the indicator colour to a colour chart. you can find out what kind of substance has been added.

Using un-reactive metals.

The two nails in the photograph look very different' The top one has been taken straight from the packet. It is still shiny. The bottom one has been in acid for a week. The acid has reacted with the iron in the nail and has started to eat it away. The nail has rusted or corroded.

A metal corrodes whenever a chemical attacks its surface. Water, air, and acid are three of the most common corroding chemicals.

How reactive are metals?

When you put a piece of magnesium into water, bubbles of hydrogen gas are produced. The bubbles appear very, very slowly. It could take about a week to collect enough hydrogen to 'pop'.

When you put a piece of magnesium into dilute hydroelectric acid, hydrogen gas bubbles off quickly.