The Whole of AQA - CHEMICAL CHANGES. GCSE 9-1 Chemistry or Combined Science Revision Topic 4 for C1

Summary

This AQA Chemistry summary covers key topics in chemical changes, including the reactivity series of metals, electrolysis, redox reactions, and the formation of salts. The script explains how different metals are extracted, with more reactive metals requiring electrolysis. It details the processes of acid-base reactions, titrations, and gas tests. The script also covers the structure of ionic compounds and electrolysis in aluminum production. With practical tips on understanding equations, mnemonics, and conducting experiments, this summary offers essential insights for students preparing for chemistry exams.

Takeaways

• 😀 Metals are ranked in the reactivity series, with the most reactive at the top and the least reactive at the bottom. More reactive metals require electrolysis for extraction.
• 😀 Metals above carbon require electrolysis for extraction, while those below carbon can be extracted by reduction.
• 😀 Unreactive metals like gold, silver, and copper are often found in their pure form in the Earth as they don’t easily react with other substances.
• 😀 Electrolysis involves oxidation (loss of electrons) at the anode and reduction (gain of electrons) at the cathode, with metal ions moving to the cathode and non-metal ions to the anode.
• 😀 In displacement reactions, the more reactive metal replaces the less reactive metal in a compound (e.g., calcium displacing magnesium).
• 😀 The neutralization equation, where hydrogen ions react with hydroxide ions to form water, is key in understanding acid-base reactions.
• 😀 Titrations are used to calculate the concentration of an unknown solution by neutralizing it with a solution of known concentration. Indicators like phenolphthalein and methyl orange help detect the endpoint.
• 😀 Strong acids dissociate completely into hydrogen ions, while weak acids dissociate partially. Concentration refers to the amount of acid or alkali in a solution.
• 😀 Electrolysis setups with different ionic compounds (like sodium chloride, copper chloride, copper sulfate) produce different gases, including hydrogen, chlorine, and oxygen.
• 😀 To prepare pure salts, such as copper sulfate, react an acid (e.g., sulfuric acid) with an appropriate metal oxide, then evaporate the solution to form crystals.

Q & A

What is the difference between how metals are extracted above and below carbon in the reactivity series?

Metals above carbon require electrolysis for extraction, while metals below carbon can be extracted through reduction.

What is the significance of the reactivity series in predicting the products of electrolysis?

The reactivity series helps predict the products of electrolysis. If a metal is more reactive than hydrogen, hydrogen gas will be produced at the cathode; if less reactive, a different gas will be released.

What happens in a displacement reaction when magnesium chloride reacts with calcium?

Calcium, being more reactive than magnesium, displaces magnesium from magnesium chloride, producing calcium chloride and magnesium.

What is the mnemonic to remember the relationship between oxidation and reduction?

The mnemonic for oxidation and reduction is 'OILRIG,' where Oxidation is Loss of electrons and Reduction is Gain of electrons.

How do you identify the positive and negative electrodes in electrolysis?

The positive electrode is the anode, and the negative electrode is the cathode. You can remember this with the mnemonic 'PANiC' (Positive Anode, Negative Cathode).

What is the process of making copper sulfate from sulfuric acid and copper oxide?

To make copper sulfate, sulfuric acid is mixed with copper oxide, heated, and stirred until in excess. After filtration to remove excess copper oxide, the solution is evaporated to form blue copper sulfate crystals.

What are the products when an acid reacts with a metal carbonate?

When an acid reacts with a metal carbonate, the products are salt, water, and carbon dioxide.

What is the difference between strong and weak acids?

Strong acids fully dissociate into hydrogen ions and other ions in solution, while weak acids only partially dissociate, meaning some hydrogen ions remain unseparated.

How does the pH scale relate to acidity and alkalinity?

The pH scale measures acidity and alkalinity. A pH of 1 is highly acidic, 7 is neutral, and 14 is highly alkaline. Acidity is caused by hydrogen ions, while alkalinity is caused by hydroxide ions.

What are the key steps in performing a titration?

In a titration, 25 cm³ of alkali is added to a conical flask, along with an indicator. Acid of known concentration is then added drop by drop from a burette until a permanent color change is observed. The volume of acid used is recorded and used for calculations.