3.1

Formulae

12 flashcards to master Formulae

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Definition Flip

Define molecular formula.

Answer Flip

The molecular formula shows the number and type of different atoms in one molecule of a compound.

Example: The molecular formula for glucose is C₆H₁₂O₆, indicating 6 carbon, 12 hydrogen, and 6 oxygen atoms.
Definition Flip

Define empirical formula.

Answer Flip

The empirical formula shows the simplest whole number ratio of the different atoms or ions in a compound.

Example: The empirical formula for glucose (C₆H₁₂O₆) is CH₂O.
Definition Flip

What does a symbol equation show?

Answer Flip

A symbol equation shows how reactants form products using chemical symbols and formulae, including state symbols (s, l, g, aq).

Example: 2H₂(g) + O₂(g) → 2H₂O(l).
Definition Flip

What are the standard state symbols and what do they represent?

Answer Flip

The state symbols are (s) for solid, (l) for liquid, (g) for gas, and (aq) for aqueous solution (dissolved in water).

Example: NaCl(s) means solid sodium chloride.
Key Concept Flip

How do you deduce the formula of an ionic compound from charges on the ions?

Answer Flip

The overall charge of an ionic compound must be neutral. Use the charges to balance the ions.

Example: Aluminum (Al³⁺) and Oxygen (O²⁻) combine to form Al₂O₃ (2 x +3 = +6, 3 x -2 = -6).
Key Concept Flip

What is the formula for carbon dioxide?

Answer Flip

The formula for carbon dioxide is CO₂. One carbon atom covalently bonded to two oxygen atoms. It is a greenhouse gas.

Key Concept Flip

What is the formula for methane?

Answer Flip

The formula for methane is CH₄. One carbon atom covalently bonded to four hydrogen atoms. It is the main component of natural gas.

Key Concept Flip

What is the formula for water?

Answer Flip

The formula for water is H₂O. Two hydrogen atoms covalently bonded to one oxygen atom. It is essential for life.

Key Concept Flip

Give three examples of a Calcium compound.

Answer Flip

Three examples of calcium compounds are calcium hydroxide (Ca(OH)₂), lime (CaO) and limestone (CaCO₃). Calcium is a group 2 metal.

Definition Flip

What are the conditions at equilibrium?

Answer Flip

At equilibrium, the rate of forward reaction = rate of reverse reaction, and the concentrations of reactants and products are constant/unchanging. The reaction is dynamic.

Key Concept Flip

How do you calculate the number of moles, given volume and concentration?

Answer Flip

Moles = (Volume in cm³/1000) * Concentration in mol/dm³.

Example: 50.0 cm³ of 0.200 mol/dm³ HCl gives moles of HCl = (50.0/1000) * 0.200 = 0.01 mol.
Definition Flip

State the effect of carbon monoxide on the body.

Answer Flip

Carbon monoxide reduces the oxygen-carrying capacity of the blood. This causes breathing problems, drowsiness, headaches, sickness, or even death.

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2.4 Structure and properties 3.2 Equations

Key Questions: Formulae

Define molecular formula.

The molecular formula shows the number and type of different atoms in one molecule of a compound.

Example: The molecular formula for glucose is C₆H₁₂O₆, indicating 6 carbon, 12 hydrogen, and 6 oxygen atoms.
Define empirical formula.

The empirical formula shows the simplest whole number ratio of the different atoms or ions in a compound.

Example: The empirical formula for glucose (C₆H₁₂O₆) is CH₂O.
What does a symbol equation show?

A symbol equation shows how reactants form products using chemical symbols and formulae, including state symbols (s, l, g, aq).

Example: 2H₂(g) + O₂(g) → 2H₂O(l).
What are the standard state symbols and what do they represent?

The state symbols are (s) for solid, (l) for liquid, (g) for gas, and (aq) for aqueous solution (dissolved in water).

Example: NaCl(s) means solid sodium chloride.
What are the conditions at equilibrium?

At equilibrium, the rate of forward reaction = rate of reverse reaction, and the concentrations of reactants and products are constant/unchanging. The reaction is dynamic.

About Formulae (3.1)

These 12 flashcards cover everything you need to know about Formulae for your Cambridge IGCSE Chemistry (0620) exam. Each card is designed based on the official syllabus requirements.

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