acids and alkalis
PH scale
The pH scale shows how acidic a substance is. It can be measured using a pH meter which gives a numerical value.
The pH scale ranges from 0 (very acidic) through 7 (neutral) to 14 (very alkaline).
pH can be also be measured using an indicator and comparing the colour with a comparison chart.
The pH scale is a number scale from 0 to 14. It tells us how acidic or alkaline an aqueous solution is. The pH scale is used to classify solutions as acidic, alkaline or neutral.The pH scale is a number scale from 0 to 14.
Neutral solutions are exactly pH 7.
Acidic solutions have pH values less than 7. The closer to pH 0, the more acidic a solution is.
Alkaline solutions have pH values more than 7. The closer to pH 14, the more alkaline a solution is.
neutralisation reactions
An acid and alkali will neutralise each other and produce a salt and water. This is called a neutralisation reaction.
The name of the salt produced can be worked out from the names of the acid and the alkali.
Chemical equations can be written to describe a neutralisation reaction.
A chemical reaction happens if you mix together an acid and a base. The reaction is called neutralisation. A neutral solution is made if you add just the right amount of acid and base together.
Word equations
Neutralisation reactions can be described using chemical equations like a word equation. This uses the scientific names for the acid and alkali placed on the reactant side of the equation. The scientific name for the salt goes on the product side, together with water.
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For example:
Nitric acid + sodium hydroxide → sodium nitrate + water
Acid + alkali → salt + water
reactions of acids and metals
Acids react with most metals.
When an acid reacts with a metal, the products are a salt and hydrogen.
This is the general word equation for the reaction: metal + acid → salt + hydrogen
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Metals and acids
Acids react with some metals to produce a salt and hydrogen gas.
Metal + acid → salt + hydrogen
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When a metal is put in acid, it gets smaller and smaller as it gets used up in the chemical reaction.
At the same time, bubbles of gas can be seen. The bubbles produced in the reaction are hydrogen gas.
This can be proven using a burning splint because hydrogen is flammable. When the burning splint is put into the test tube containing hydrogen gas, a small explosion occurs, making a squeaky pop sound. This shows that hydrogen is present.
reactivity of metalsSome metals are very reactive. This means they easily take part in chemical reactions to make new substances. Other metals are very unreactive, and do not easily take part in chemical reactions.
If we put the metals in order of their reactivity, from the most reactive down to the least reactive, we get a list called the reactivity series.