Acid Attack
What acids react with and what they make: a salt and hydrogen with a metal, a salt and water with a base, a salt, water and carbon dioxide with a carbonate, plus neutralisation, the pH scale, and how to prepare a pure dry salt.
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What acids attack, and what they leave
Acids are reactive, and what they make depends on what they meet. React one with a metal, a base or a carbonate and you always get a salt, but the rest of the products change. This module works through the three acid reactions, neutralisation and the pH scale, and how chemists turn an acid into a pure, dry salt in the lab.
Acid words to know
Learn these before you mix anything.
Two reactions that fizz
Both give off a gas, but not the same one.
Work out the products from what reacts
In the exam, work out the products from what reacts. Every acid reaction makes a salt; the rest depends on the partner. A metal also releases a flammable gas; a carbonate also releases the gas that clouds limewater plus water; a base or alkali simply adds water. For the salt-prep practical, use more of the insoluble solid than you need so every bit of acid is used up, then filter off what is left and evaporate to crystallise.
Match the reaction
- acid with a metal
- acid with an alkali
- acid with a carbonate
- an acidic solution
- makes a salt and hydrogen
- makes a salt and water
- makes a salt, water and carbon dioxide
- has a pH below 7
Match the pH
- pH 1
- pH 7
- pH 13
- universal indicator
- strongly acidic
- neutral
- strongly alkaline
- shows the pH by its colour
Which gas from a carbonate?
What gas is given off when an acid reacts with a metal carbonate?
- Carbon dioxide
- Hydrogen
- Oxygen
- Chlorine
True about acids
Select the TWO true statements about the reactions of acids.
- An acid reacting with a metal makes a salt and hydrogen
- Neutralisation makes a salt and water
- Alkalis have a pH below 7
- An acid and a carbonate make only a salt
Find the neutral point
The pH scale runs from 0 to 14, and the neutral point sits exactly in the middle. Add 0 and 14 and divide by 2 to find the neutral pH. What is the answer?
Order the salt preparation
Put the steps of making a pure dry salt in order, earliest first.
- Add excess insoluble base to the warm acid
- Filter off the leftover base that did not react
- Evaporate some of the water from the solution
- Leave it to crystallise into a pure dry salt
Complete the rules
The reaction of an acid with a base to make a salt and water is called _____. An acid with a metal produces a salt and _____. An acid with a carbonate also produces water and _____ dioxide. On the pH scale a neutral solution has a pH of _____.
Spot the correct products
Tap the TWO correct products of acid reactions.
- an acid and a metal make hydrogen
- an acid and a carbonate make carbon dioxide
- an acid and a metal make oxygen
- an acid and a base make hydrogen
Name the gas or the reason
Read each case and choose the best answer.
- You add an acid to a metal and it fizzes, giving off a gas that pops with a lit splint. What gas is it?
- You add an acid to a carbonate and it fizzes, giving off a gas that turns limewater cloudy. What gas is it?
- In the salt-prep practical, why is the insoluble base added in excess?
Explain the reactions of acids
Explain the reactions of acids and how a pure, dry salt is made from an acid and an insoluble base.
- Give the products of an acid with a metal, a base and a carbonate
- Explain what neutralisation is and the pH of a neutral solution
- Describe the steps to make a pure dry salt and say why excess base is used