Chemistry (9202) | Metals

🔬 Welcome to the World of Metals!

Hello future Chemists! This chapter is all about Metals – not just what they look like, but how they behave when things get spicy (chemically speaking!). We are focusing on the section "Chemical changes," so get ready to explore reactions, explosions, and how we get shiny metals out of dull rocks.

Don't worry if this seems tricky at first. We will break down every concept, especially the all-important Reactivity Series, using simple steps and fun analogies. Let's make chemistry click!

💡 Section 1: Chemical Properties and Reactions of Metals

While metals share physical properties (like being shiny and conducting electricity), their chemical behavior—how they react—varies hugely. This variation is the foundation of the entire chapter!

1.1 Reaction with Oxygen (Oxidation)

When a metal reacts with oxygen (usually when heated), it forms a metal oxide. This process is known as oxidation.

• Very reactive metals (like Sodium, Potassium) react instantly, even at room temperature.
• Less reactive metals (like Iron, Copper) require strong heating to react.
• Unreactive metals (like Gold, Platinum) do not react with oxygen at all, which is why they stay shiny forever!

General Word Equation:
Metal + Oxygen \(\rightarrow\) Metal Oxide

Did you know? The flash you see when magnesium burns is the metal reacting violently with oxygen in the air, releasing light and heat energy!

1.2 Reaction with Water (Steam or Liquid)

Metals react differently with water depending on their reactivity and whether the water is cold or hot (steam).

A. Very Reactive Metals (K, Na, Ca)

These metals react with cold water, producing a metal hydroxide and hydrogen gas.

Equation Example (Sodium):
Sodium + Water \(\rightarrow\) Sodium Hydroxide + Hydrogen
\(2\text{Na}(s) + 2\text{H}_2\text{O}(l) \rightarrow 2\text{NaOH}(aq) + \text{H}_2(g)\)

Observation: You will see fizzing (hydrogen gas) and the metal often floats and moves quickly on the water surface.

B. Moderately Reactive Metals (Mg, Zn, Fe)

These metals only react when heated and exposed to steam, producing a metal oxide and hydrogen gas.

Equation Example (Magnesium):
Magnesium + Steam \(\rightarrow\) Magnesium Oxide + Hydrogen
\(\text{Mg}(s) + \text{H}_2\text{O}(g) \rightarrow \text{MgO}(s) + \text{H}_2(g)\)

1.3 Reaction with Dilute Acids

Most metals react with dilute acids (like dilute Hydrochloric acid or Sulfuric acid) to produce a salt and hydrogen gas.

The speed of the reaction (fizzing rate) tells you how reactive the metal is.

• Potassium and Sodium react violently (too dangerous for school labs!).
• Magnesium reacts very quickly.
• Iron reacts slowly.
• Copper, Silver, and Gold do not react at all.

General Word Equation:
Metal + Dilute Acid \(\rightarrow\) Salt + Hydrogen Gas

Equation Example (Zinc and HCl):
Zinc + Hydrochloric Acid \(\rightarrow\) Zinc Chloride + Hydrogen
\(\text{Zn}(s) + 2\text{HCl}(aq) \rightarrow \text{ZnCl}_2(aq) + \text{H}_2(g)\)

📍 Section 2: The Reactivity Series and Displacement

2.1 Understanding the Reactivity Series

The Reactivity Series is a list of metals (and sometimes non-metals like Carbon and Hydrogen) arranged in order of decreasing reactivity. The metals at the top are the most reactive; the ones at the bottom are the least reactive.

Why is this important? It predicts how a metal will react and how easily it can be extracted from its ore.

Here is the simplified series, with Carbon (C) and Hydrogen (H) included because they are crucial reference points for extraction and reactions:

🧩 Memory Aid (Mnemonic):
To help remember the order (down to Hydrogen):
Katie Now Can Make A Cute Zebra For People Hungry.

2.2 Displacement Reactions

The most important concept derived from the Reactivity Series is displacement. A more reactive metal can displace (kick out) a less reactive metal from a solution of its salt.

Analogy: Think of a strong team playing a weak team. The strong team (more reactive metal) can easily replace the weak team (less reactive metal) on the field (in the compound).

If Metal A is more reactive than Metal B:

Metal A + Salt of Metal B \(\rightarrow\) Salt of Metal A + Metal B

Example: Zinc is more reactive than Copper.

Zinc + Copper Sulfate \(\rightarrow\) Zinc Sulfate + Copper
\(\text{Zn}(s) + \text{CuSO}_4(aq) \rightarrow \text{ZnSO}_4(aq) + \text{Cu}(s)\)

Observation: The blue copper sulfate solution will become colourless (zinc sulfate is colourless), and a reddish-brown solid (copper metal) will form on the zinc surface.

Important Rule: If the metal added is *less* reactive than the metal in the salt solution, NO REACTION occurs.

🔩 Section 3: Extracting Metals from Their Ores

Except for very unreactive metals (like Gold), most metals are found in the Earth's crust combined with other elements (usually Oxygen) as compounds called ores. We need chemical changes to get the pure metal back.

3.1 Linking Reactivity to Extraction Method

The method used to extract a metal depends entirely on its position in the Reactivity Series. We are trying to achieve reduction – separating the metal from its compound.

A. Highly Reactive Metals (Above Carbon: K, Na, Ca, Mg, Al)

These metals have a very strong attraction to the oxygen in their ores. They cannot be easily reduced using common cheap substances like Carbon.

• Extraction Method: Electrolysis (using electricity to force the chemical change).
• This is very expensive due to the high energy needed, but it is necessary to overcome the metal's high reactivity.

B. Moderately Reactive Metals (Below Carbon, Above Hydrogen: Zn, Fe, Pb)

These metals are less reactive than Carbon. Because Carbon is a more reactive non-metal, it can displace the metal from its oxide.

• Extraction Method: Heating with Carbon (or Carbon Monoxide).
• Carbon is used as a reducing agent. It removes the oxygen from the metal oxide, leaving the pure metal.

Example (Iron):
Iron Oxide + Carbon \(\rightarrow\) Iron + Carbon Dioxide

C. Low Reactivity Metals (Below Hydrogen: Cu, Ag, Au)

These metals are so unreactive that they are often found naturally in their uncombined element state (native state).

• Extraction Method: Found free, or simple heating is enough for slight impurities.

🧬 Section 4: Corrosion and Prevention

4.1 What is Corrosion?

Corrosion is the destructive chemical process that occurs when metals react with substances in the environment (air and water).

The most common and economically significant type of corrosion is the rusting of iron.

Rusting (Corrosion of Iron)

Rust is hydrated iron(III) oxide. For iron to rust, two conditions must be present simultaneously:

1. Oxygen (from the air)
2. Water

Chemical change:
Iron + Water + Oxygen \(\rightarrow\) Hydrated Iron(III) Oxide (Rust)

Crucial Test: If you put an iron nail in boiled water (which removes dissolved oxygen) or in dry air (which removes water), it will not rust.

4.2 Preventing Corrosion

Since corrosion requires both oxygen and water, prevention methods focus on excluding one or both of these substances from the metal surface.

A. Barrier Methods

These methods put a physical layer between the iron and the environment.

• Painting: Simple and cheap for large structures (like bridges).
• Oiling/Greasing: Used for moving parts (like bike chains or machine gears).
• Plating (e.g., Chromium): Coating the iron with a layer of a less reactive metal.
• Galvanising: Coating iron with a layer of Zinc.

B. Sacrificial Protection (The Clever Method)

This method is more robust and relies on the Reactivity Series.

• The iron object is connected to a block of a more reactive metal (usually Zinc or Magnesium).
• Because the reactive metal is higher up the series, it loses its electrons and corrodes instead of the iron. It "sacrifices" itself to save the iron.

This method is especially useful for large underground pipes or ships’ hulls, where repairing a simple barrier layer is impossible.

Key Takeaway: Corrosion is an unwanted oxidation reaction. Prevention techniques involve stopping the iron from reacting by using physical barriers or by forcing a more reactive metal to oxidize first.

🏆 Chapter Summary Checklist

• ✔ I can describe how metals react with O₂, H₂O, and dilute acids.
• ✔ I know the order of the Reactivity Series (K down to Au).
• ✔ I can explain and predict displacement reactions using the series.
• ✔ I know why electrolysis is needed for highly reactive metals.
• ✔ I know why Carbon can be used to extract metals like Iron (reduction).
• ✔ I know the two conditions necessary for rusting (water and oxygen).
• ✔ I can distinguish between barrier methods and sacrificial protection.