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Elements (Substances)

CSCA Elements (Substances) study guide organized around the publicly available CSCA syllabus. Practice Chemistry questions on aicsca.com.

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This study guide is organized around the publicly available CSCA syllabus for international undergraduate applicants.

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Elements (Substances)

1. Core Tool: The Metal Activity Series

This is the "master key" for solving metal reaction problems. You must master not just the order, but the **boundary lines**.

**Key Rules & Exam Traps:**

1. **Reaction with Acids (Boundary: H)**:

* Metals **before H** can displace Hydrogen gas from dilute HCl or dilute $H_2SO_4$.

* **Exception Warning**: **Nitric Acid ($HNO_3$)** and **Concentrated Sulfuric Acid** are strong oxidizing agents. They react with metals to produce water and nitrogen/sulfur oxides, **NOT Hydrogen**.

2. **Reaction with Water (Boundary: Mg)**:

* **K, Ca, Na**: Extremely active. React violently with cold water to form alkali and $H_2$.

* **Mg**: Reacts slowly with cold water, noticeably with boiling water.

* **Al and beyond**: Do not react with water at room temperature.

3. **Reaction with Salt Solutions**:

* Rule: **"Left displaces Right"** (More active metal displaces less active metal).

* **Trap**: If you put K, Ca, or Na into a $CuSO_4$ solution, they will **NOT** displace Cu directly. They react with the water first.

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2. High-Frequency Metal Topics

#### A. Sodium (Na) - Representative Active Metal

* **Phenomenon**: When Na is dropped into water (with phenolphthalein), remember: "**Float, Melt, Swim, Hiss, Red**".

* **Float**: Density < Water.

* **Melt**: Exothermic reaction + low melting point $\rightarrow$ forms a ball.

* **Swim & Hiss**: Generated gas ($H_2$) pushes the ball.

* **Red**: Forms $NaOH$ (alkaline).

* **Equation**: $2Na + 2H_2O \rightarrow 2NaOH + H_2\uparrow$

#### B. Aluminum (Al) - Amphoteric Metal

This is a critical differentiation point in CSCA exams. Al reacts with both strong acids and strong bases.

* With Acid: $2Al + 6HCl \rightarrow 2AlCl_3 + 3H_2\uparrow$

* **With Base (Focus)**: $2Al + 2NaOH + 2H_2O \rightarrow 2NaAlO_2 + 3H_2\uparrow$

#### C. Iron (Fe) - Variable Valency

The exam often tests whether Fe forms +2 or +3 valency states.

| Oxidizer Strength | Product Valency | Typical Equation |

| :--- | :--- | :--- |

| **Weak** ($H^+, Cu^{2+}, S, I_2$) | **+2 ($Fe^{2+}$)** | $Fe + 2HCl \rightarrow FeCl_2 + H_2\uparrow$ |

| **Strong** ($Cl_2, Br_2, HNO_3$) | **+3 ($Fe^{3+}$)** | $2Fe + 3Cl_2 \xrightarrow{ignite} 2FeCl_3$ |

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3. High-Frequency Non-Metal Topics

#### A. Chlorine ($Cl_2$) - Strong Oxidizer

* **Properties**: Yellow-green, toxic gas.

* **Reaction with Alkali (Bleach Production)**:

* $Cl_2 + 2NaOH \rightarrow NaCl + NaClO + H_2O$

* Point: $Cl_2$ acts as both oxidizer and reducer (Disproportionation).

#### B. Carbon (C) & Silicon (Si)

* **Carbon**: Reducing agent at high temps (used to smelt metals from oxides).

* **Silicon (Si)**: Semiconductor material. Chemically stable, but dissolves in Hydrofluoric acid ($HF$) and strong bases ($NaOH$).