Zainab Al-Hassani (Y9): Substances and Reactions in Chemistry

Last term in Chemistry, we explored how different substances react and how to represent these reactions using scientific terminology and chemical symbols. Our lessons focused on chemical changes, the conservation of mass, and how acids react with various materials. Alongside this, we have been developing our practical skills by learning how to plan and carry out experiments methodically. 

We began by examining what happens during a chemical reaction. When new substances are formed, atoms are rearranged but never lost or created. This principle is known as the conservation of mass. For instance, when magnesium reacts with oxygen, the total mass of the products is equal to the mass of the reactants. This concept helps us understand why chemical reactions must be balanced. 

Next, we learnt how to construct both word and symbol equations to describe reactions accurately. Chemical equations show which substances are involved in a reaction and what products are formed. For example, the reaction between hydrochloric acid and calcium hydroxide can be written as: 

We then moved on to neutralisation reactions, where an acid reacts with an alkali to produce a salt and water. We used indicators like universal indicator and litmus paper to monitor pH changes during the reactions and determine when the solution became neutral. One example we investigated was the reaction between sulphuric acid and calcium hydroxide, which forms calcium sulfate and water.

Following this, we explored reactions between acids and carbonates. These reactions produce a salt, water, and carbon dioxide, which we could observe as effervescence. To confirm the presence of carbon dioxide, we could bubble the gas through lime water, which would turn cloudy. An example of this reaction is: 

Hydrochloric acid + Calcium Carbonate → Calcium Chloride + Water + Carbon Dioxide 

In later lessons, we studied how acids react with metals. These reactions also form a salt and a gas - this time hydrogen. To test for hydrogen, we used a lit splint and listened for a “squeaky-pop” sound, which confirms the presence of the gas. For example:

Hydrochloric acid + Zinc → Zinc Chloride + Hydrogen

Towards the end of the topic, we focused on developing our experimental skills. This involved planning investigations, identifying variables, and recording data accurately. One practical involved measuring how the concentration of hydrochloric acid affects the rate of reaction with different metals. We wrote a complete method, collected accurate results in a table, and drew conclusions based on the data we gathered.

Overall, this topic has helped us understand how acids and bases react with different substances, and how to write and balance chemical equations. Many of us have gained confidence in practical work, from planning them to recording results clearly. This has helped us further our understanding and knowledge in chemistry.

Zainab Al-Hassan - Year 9 Science Prefect