A-Level Chemistry (AQA) > 3.2.4 Period 3 oxides > Flashcards

3.2.4 Period 3 oxides Flashcards

Classify Period 3 oxides by predicting their acid–base behavior and reactions with water and oxygen. (35 cards)

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1
Q

What type of trend occurs in the oxides of Period 3 elements from sodium to sulfur?

A

Basic to acidic

Oxides change from basic → amphoteric → acidic across the period.

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2
Q

What type of oxide is sodium oxide when it reacts with water?

A

Basic oxide

Na2O reacts with water to form sodium hydroxide solution.

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3
Q

Fill in the blank:

Sodium oxide reacts with water to produce sodium _______.

A

hydroxide

Na2O + H2O → 2NaOH, forming a strongly alkaline solution.

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4
Q

True or False:

Magnesium oxide forms an alkaline solution when reacting with water.

A

True

MgO reacts slowly with water to form Mg(OH)2.

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5
Q

Which Period 3 oxide is amphoteric and reacts with both acids and bases?

A

Aluminium oxide

Al2O3 shows both acidic and basic behaviour.

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6
Q

True or False:

Silicon dioxide reacts readily with water to form an acidic solution.

A

False

SiO2 does not react with water due to its giant covalent structure.

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7
Q

Fill in the blank:

Phosphorus(V) oxide reacts with water to form _______ acid.

A

phosphoric

P4O10 + H2O forms H3PO4.

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8
Q

What type of oxides are sulfur dioxide and sulfur trioxide?

A

Acidic oxides

They react with water to form sulfurous and sulfuric acids.

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9
Q

True or False:

Sulfur trioxide reacts with water to form sulfuric acid.

A

True

SO3 + H2O → H2SO4.

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10
Q

Why does silicon dioxide have a very high melting point?

A

Giant covalent structure

Strong covalent bonds extend throughout the lattice.

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11
Q

Fill in the blank:

Sodium oxide and magnesium oxide have high melting points due to strong _______ bonding.

A

ionic

Ionic lattices require large amounts of energy to break.

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12
Q

How does the pH of solutions formed by Period 3 oxides generally change from Na to S?

A

Decreases

Solutions change from strongly alkaline to acidic across the period.

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13
Q

Observations when sodium reacts with water

A

Floats, melts into a ball, moves rapidly, fizzing (H₂), may ignite

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14
Q

How does magnesium react with cold water?

A

Very slow reaction forming magnesium hydroxide and hydrogen

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15
Q

How does magnesium react with steam?

A

Reacts faster to form magnesium oxide and hydrogen

Equation: Mg + H₂O(g) → MgO + H₂

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16
Q

What oxides do Na–S form with oxygen?

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A

Na₂O, MgO, Al₂O₃, SiO₂, P₄O₁₀, SO₂, SO₃

17
Q

Which oxides are simple molecular?

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A

P₄O₁₀, SO₂, SO₃

18
Q

Trend in melting point of oxides Na → S

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A

Increases (Na₂O → Al₂O₃), then decreases sharply (SiO₂ → SO₃)

Increases from Na₂O → Al₂O₃ due to stonger ionic bonding. SiO₂ has the highest melting point due to giant covalent structure with many strong bonds. From P₄O₁₀ the melting point decreases because they are simple molecular with weak intermolecular forces.

19
Q

Does Al₂O₃ react with water?

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A

No (insoluble, amphoteric oxide)

20
Q

What happens when SO₂ reacts with water?

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A

Forms sulfurous acid (H₂SO₃, weak acid)

21
Q

Anion formed from phosphoric acid

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A

PO₄³⁻ (phosphate)

22
Q

Anion from sulfurous acid

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A

SO₃²⁻ (sulfite)

23
Q

Anion from sulfuric acid

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A

SO₄²⁻ (sulfate)

24
Q

How do basic oxides react with acids?

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A

Neutralisation → salt + water

25
How do **acidic oxides** react with bases?
Forms a salt and water in a neutralisation reaction
26
How does **Al₂O₃ react with acid**?
Al₂O₃ + 6HCl → 2AlCl₃ + 3H₂O
27
How does **Al₂O₃ react with base**?
Al₂O₃ + 2NaOH + 3H₂O → 2NaAl(OH)₄
28
Observation when **magnesium reacts with oxygen**?
Burns with bright white flame to form MgO
29
How does **sodium react with oxygen**?
Very vigorously to form sodium oxide (Na₂O)
30
How does **aluminium react with oxygen**?
Forms Al₂O₃ but reaction is limited bry protective oxide layer
31
How does **silicon react with oxygen**?
Reacts at high temperature to form SiO₂
32
How does **phosphorus react with oxygen**?
Burns readily to form P₄O₁₀ (white smoke)
33
Observation when **sulfur reacts with oxygen**?
Burns with blue flame to form SO₂ (can further oxidise to SO₃)
34
pH of NaOH
14
35
What is the **pH of Mg(OH)₂ in water**?
9–10 ## Footnote because it is only slightly soluble, so it produces a low concentration of OH⁻ ions
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