AQA GCSE FOUNDATION Chemistry: Preparing Soluble Salts

Preparing Soluble Salts: A Foundation Chemistry Tutorial

This tutorial explores the preparation of soluble salts through the reaction of an acid with an insoluble base, followed by evaporation and crystallization. We'll also delve into calculating yield and purity, as well as understanding the reaction type.

The Process

1. Reaction: Start by reacting an acid with an insoluble base. The acid will be in excess to ensure complete reaction.
2. Filtration: After the reaction, filter the mixture to remove the unreacted base. This leaves a solution containing the soluble salt.
3. Evaporation: Gently heat the solution to evaporate the water. As the water evaporates, the concentration of the salt increases, leading to crystallization.
4. Crystallization: As the solution continues to evaporate, the salt will crystallize out of the solution. This process can be accelerated by cooling the solution.

Example: Preparing Copper Sulfate Crystals

Let's prepare copper sulfate crystals using copper oxide as the insoluble base and sulfuric acid as the acid.

1. Reaction: Combine copper oxide (CuO) with dilute sulfuric acid (H2SO4). The reaction proceeds as follows:

   CuO(s) + H2SO4(aq) ? CuSO4(aq) + H2O(l) 2. Filtration: Filter the mixture to remove any unreacted copper oxide. 3. Evaporation: Heat the solution gently to evaporate the water. 4. Crystallization: As the water evaporates, blue copper sulfate crystals will form.

Calculating Yield and Purity

• Yield: The yield is the amount of product obtained in a reaction, compared to the theoretical yield. The theoretical yield is the maximum amount of product that can be formed based on the starting materials. To calculate the yield, use the following formula:

Yield = (Actual yield / Theoretical yield) x 100%

• Purity: The purity of a substance refers to the percentage of the desired compound present in the sample. This is determined by analyzing the sample and comparing it to a known standard.

Understanding the Reaction Type

The reaction between an acid and an insoluble base is a neutralization reaction. The acid provides hydrogen ions (H+) and the base provides hydroxide ions (OH-). These ions react to form water (H2O), releasing heat and forming a salt.

Key Points

• Safety: Always wear appropriate safety equipment, such as goggles and gloves, when handling chemicals.
• Heating: Be careful when heating solutions. Ensure they are heated gently and not left unattended.
• Evaporation: To ensure complete crystallization, evaporate the solution slowly to prevent the salt from splattering.

By following these steps and applying the provided information, you can successfully prepare soluble salts and understand the underlying chemical principles involved.