← Chemistry F4–F6

CHEMISTRY IONS

HKDSE Interactive Matrix v2.2

HKDSE Chemistry Curriculum

Master Chemical Ions & Compounds

Interactive cross-method builder, ion flashcards, ionic compound formulation, and challenging HKDSE mixed MC quizzes.

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The Cross Method Rules

Charge numbers swap to become subscripts. Polyatomic ions require brackets ( ) if subscript > 1.

Cross Method Visual Derivation Tool

Select any Cation and Anion to visually trace charge transposition and formula generation in real time.

1. Select Cation (Positive Ion):

2. Select Anion (Negative Ion):

Step-by-Step Derivation View

Cation

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Anion

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⬇ Charge Swapping & Ratio Simplification ⬇

Cross charges...

Resulting Ionic Compound

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Part 1: Ion Memorization Practice

Test your knowledge of ion symbols, ionic charges, and names with HKDSE Multiple Choice questions.

Question 1/10 Score: 0

What is the formula for:

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Part 2: Ionic Compound Formulation

Combine cations and anions using the Cross Method to choose correct chemical formulas & IUPAC names.

Question 1/10 Score: 0

Combine these ions using the Cross Method:

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Select the correct formula & IUPAC name:

Part 3: Master Challenge MC Quiz

Comprehensive test on Ion Names, Formulas, Charges & Compound Formation

Question 1/10 Score: 0

Question Prompt:

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Select the correct answer choice:

Quiz Completed!

Enter your student information to generate an official downloadable PDF Performance & Mistake Analysis Report.

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Class:

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The Cross Method Rules & Examples

Write the cation charge on the left and anion charge on the right.
Omit + and - signs. Cross charge numbers to opposite subscripts.
Simplify the ratio to lowest whole integers if necessary.
If a polyatomic ion requires a subscript > 1, enclose it in brackets ( ).

Example 1: Polyatomic Ion with Brackets

iron(III) sulphate: Fe³⁺ + SO₄^2-

Swap charge values (3 & 2) → Subscript ratio 2:3

Fe₂(SO₄)₃ (iron(III) sulphate)

Example 2: Monatomic Ion Ratio

sodium oxide: Na⁺ + O^2-

Swap charge values (1 & 2) → Subscript ratio 2:1

Na₂O (sodium oxide)

Example 3: 1:1 Ratio Polyatomic Ion

potassium hydroxide: K⁺ + OH^-

Charge magnitude 1:1 → No brackets required for subscript 1

KOH (potassium hydroxide)

HKDSE Chemistry Ion Matrix Table

Ion Name	Symbol / Formula	Charge	Type	HKDSE Notes

CHEMISTRY IONS

Master Chemical Ions & Compounds

Cross Method

Part 1: Ions

Part 2: Compounds

Part 3: Master Quiz

The Cross Method Rules

Cross Method Visual Derivation Tool

Part 1: Ion Memorization Practice

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Part 2: Ionic Compound Formulation

Part 3: Master Challenge MC Quiz

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Quiz Completed!