Understanding the Empirical Formula of Hydrated Compounds

What is the empirical formula of a hydrated compound with 5 water molecules of crystallisation?

• A. MH5O
• B. M(H2O)5
• C. M·5H2O
• D. MH10

Answer: (C)

The empirical formula of a hydrated compound represents the simplest whole-number ratio of the elements in that compound. In the case of a hydrated compound with 5 water molecules of crystallization, the correct representation accounts for both the metal ion (M) and the associated water molecules. When you see the notation M·5H2O, it clearly indicates that for every one metal ion (M), there are five water molecules (5H2O) associated with it. This format effectively expresses the water of crystallization in a way that underscores the stoichiometric relationship between the metal and the water. The other choices reflect different ways of expressing the relationship. For instance, MH5O suggests an incorrect molecule composition without properly conveying the association of water. M(H2O)5, while representing that there are 5 water molecules, does not clearly highlight the relationship with the metal. Meanwhile, MH10 implies that the compound consists of one metal and 10 hydrogen atoms, which does not adequately describe the presence of the water molecules. Thus, M·5H2O is the most appropriate representation for the compound, emphasizing both the metal and its five water molecules in a clear and concise manner.

When you're studying A Level Chemistry, concepts like empirical formulas can feel daunting. You know what? Understanding how hydrated compounds work is key, especially when it comes to exams like the OCR Chemistry paper. So, let’s chat about the empirical formula for a hydrated compound, particularly one that comes with 5 water molecules.

Imagine you have a metal ion, let’s call it ( M ). When it bonds with water, it forms what's known as a hydrated compound. If there are 5 water molecules associated with that metal ion, we represent it as ( M \cdot 5H_2O ). Now, why does this matter? Well, the way we express that relationship tells us a lot about the compound's structure.

Now, why is ( M \cdot 5H_2O ) the go-to answer? It highlights the connection between the metal and water molecules in the simplest way possible. Each piece plays its role—one ( M ) ion and five ( H_2O ) molecules join together in a stoichiometric dance. But, let’s take a quick detour to look at what happens with our other options, shall we?

First off, ( MH_5O ) just doesn't cut it. It mixes up elements in a way that doesn’t define the watery relationship properly. And then there's ( M(H_2O)5 ). While it does show there are five water molecules, it lacks that straightforward connection to our metal ( M ). It’s like talking about an awesome band with no knowledge of the lead singer, right? Now, let's not forget ( MH{10} ). That one’s misleading, suggesting that our compound consists of one ( M ) and ten hydrogens—but where’s the water in that?

You see, the real beauty of ( M \cdot 5H_2O ) is clarity—it's like a chemistry compass guiding you to understand how metal ions and water interact. Now, for future reference or tweaks in your studying method, here’s a friendly tip: always remember the key relationship between the metal and the water when you’re identifying empirical formulas. It’s crucial for exams and will serve you well throughout your chemistry journey.

So, the next time you come across a question about hydrated compounds during your A Level Chemistry OCR prep, remember this little chat. The connection between the metal ion and water of crystallization not only helps simplify your answers but underscores why chemistry is all about the relationships between different elements. Keep it clear, keep it concise, and you'll be on your way to mastering those exam questions!