Chapter 4: Useful Chemical Reactions

Question 1

The reactivity series from most reactive to least

Answer 1

1) Potassium
2) Sodium
3) Calcium
4) Magnesium
5) Aluminum
6) Zinc
7) Iron
8) Lead
9) Hydrogen
10) Copper
11) Mercury
12) Silver
13) Gold
14) Platinum

Question 2

What is a displacement reaction?

Answer 2

Is a more reactive element displaces – or pushes out – a less reactive element from its compound. This can also happen in solutions.

Question 3

What is electrolysis?

Answer 3

is a chemical process that uses electricity to break down a substance into its basic elements or components.

How It Works:
• An electric current is passed through a liquid or solution that contains ions (called an electrolyte).
• This causes a chemical reaction at the electrodes (the positive and negative terminals), separating the elements.

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Example: Electrolysis of Water

When electricity is passed through water (with a bit of electrolyte like salt or acid added), it splits into:
• Hydrogen gas at the cathode (negative electrode)
• Oxygen gas at the anode (positive electrode)

Common Uses of Electrolysis:
• Purifying metals (like copper)
• Electroplating (coating objects with a metal layer)
• Producing gases like hydrogen and oxygen
• Extracting metals from ores (e.g. aluminum from bauxite)

Question 4

What is an ore?

Answer 4

is a rock that you can extract a metal from, and that contains enough of the metal to make it worth extracting. Metal displacement reactions can be used to extract metals from its compound.

Question 5

Relative mass

Answer 5

Calculate the relative mass of an atom by adding its numbers of protons and neutrons.
Calculate the mass of a molecule by adding the relative masses of its atoms. This can help you work out the yield of a reaction.
The relative mass of methane, CH4 Relative mass of carbon = 12 Relative mass of hydrogen = 1
12 + (4 x 1) = 16

Question 6

Calculating yield

Answer 6

There are two common types:
• Theoretical Yield: The maximum amount that could be produced.
• Actual Yield: What was actually produced in the lab.

Percent Yield Formula:
Percent Yield = Actual Yield\Theoretical Yield x 100

Example:
You expect 10 grams from a reaction but only get 8 grams:

Percent Yield = (8\10) x 100 = 80%