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Chemistry ✦ (Form 4) > Chapter 6 (6.1 - 6.6) > Flashcards

Chapter 6 (6.1 - 6.6) Flashcards

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1
Q

What is an acid?

A

A: An acid is a chemical compound that produces hydrogen ions (H⁺) or hydroxonium ions (H₃O⁺) when dissolved in water.

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2
Q

What happens when hydrochloric acid (HCl) dissolves in water?

A

A: It dissociates into hydrogen ions (H⁺) and chloride ions (Cl⁻).
𝐻𝐶𝑙 (𝑎𝑞) →𝐻+ (𝑎𝑞) + 𝐶𝑙− (𝑎𝑞)

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3
Q

What does “basicity” of an acid refer to?

A

A: It refers to the number of hydrogen ions (H⁺) an acid molecule can produce when it ionizes in water.

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4
Q

What is a monoprotic acid?

A

A: A monoprotic acid produces one hydrogen ion (H⁺) per acid molecule.

Example: Hydrochloric acid (HCl).

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5
Q

What is a diprotic acid?

A

A: A diprotic acid produces two hydrogen ions (H⁺) per acid molecule.

Example: Sulfuric acid (H₂SO₄).

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6
Q

What is a triprotic acid?

A

A: A triprotic acid produces three hydrogen ions (H⁺) per acid molecule.

Example: Phosphoric acid (H₃PO₄).

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7
Q

What is a triprotic acid?

A

A: A triprotic acid produces three hydrogen ions (H⁺) per acid molecule.

Example: Phosphoric acid (H₃PO₄).

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8
Q

What is a base?

A

A: A base is a chemical compound that can neutralize an acid to produce salt and water.

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9
Q

What is an alkali?

A

A: An alkali is a base that is soluble in water and produces freely moving hydroxide ions (OH⁻).

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10
Q

What happens when potassium hydroxide (KOH) dissolves in water?

A

A: It dissociates into potassium ions (K⁺) and hydroxide ions (OH⁻).

𝐾𝑂𝐻 (𝑎𝑞) → 𝐾+ (𝑎𝑞) + 𝑂𝐻− (𝑎𝑞)

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11
Q

What is sulfuric acid used for?

A

A: It is used to make paints, polymers, fertilizers, and detergents.

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12
Q

What is hydrochloric acid used for?

A

A: It is used to clean metal before electroplating.

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13
Q

What is benzoic acid used for?

A

A: It is used to preserve food.

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14
Q

What is ammonia used for?

A

A: Ammonia is used to make fertilizers, nitric acid, and to maintain latex in liquid form.

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15
Q

What is magnesium hydroxide used for?

A

A: It is used to make toothpaste and gastric medicine.

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16
Q

What is calcium hydroxide used for?

A

A: It is used to make cement, limewater, and to neutralize acidic soil.

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17
Q

Why do acids only show acidic properties in the presence of water?

A

A: When an acid dissolves in water, it ionizes to produce hydrogen ions (H⁺), which give the acid its acidic properties.

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18
Q

What happens to oxalic acid (C₂H₂O₄) without water?

A

A: Without water, oxalic acid only exists as molecules, and hydrogen ions (H⁺) are not present, so the acid does not show its acidic properties.

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19
Q

What color does methyl orange turn in

an acidic solution?
an alkaline solution?

A

A: Red.

B: Yellow.

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20
Q

What color does universal indicator

turn in a strong acid?
turn in a strong alkali?

A

A: Red.

B: Purple.

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21
Q

What color does blue litmus paper turn in an acidic solution?

What color does red litmus paper turn in an alkaline solution?

A

A: Red.
B: Blue.

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22
Q

What are the indicators and their colors in an acidic solution?

Methyl orange:
Universal indicator:
Blue litmus paper:
Red litmus paper:

A

Methyl orange: Red
Universal indicator: Red for strong acid, yellow for weak acid
Blue litmus paper: Red
Red litmus paper: Red

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23
Q

What are the indicators and their colors in an alkaline solution?

Methyl orange:
Universal indicator:
Blue litmus paper:
Red litmus paper:

A

Methyl orange: Yellow
Universal indicator: Purple for strong alkali, blue for weak alkali
Blue litmus paper: Blue
Red litmus paper: Blue

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24
Q

What is the pH scale?

A

A: The pH scale determines the degree of acidity or alkalinity of a substance.

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25
Q

What is the pH value of a neutral substance?

A

A: 7

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26
Q

What does a pH value greater than 7 indicate?

A

A: It indicates an alkaline substance (OH⁻ > H⁺).

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27
Q

What does a pH value less than 7 indicate?

A

A: It indicates an acidic substance
(H⁺ > OH⁻).

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28
Q

What is the definition of pH?

A

A: pH is a logarithmic measurement of the concentration of hydrogen ions (H⁺) in an aqueous solution.

29
Q

What is the formula for calculating pH?

A

A: pH = -log[H⁺].

30
Q

What is pOH?

A

A: pOH is a logarithmic measurement of the concentration of hydroxide ions (OH⁻) in a solution.

31
Q

What is the formula for calculating pOH?

A

A: pOH = -log[OH⁻].

32
Q

What is the relationship between pH and pOH?

A

A: pH + pOH = 14.

33
Q

How do you calculate pH from pOH?

A

A: pH = 14 - pOH.

34
Q

How does the concentration of hydrogen ions (H⁺) affect the pH value?

A

A: As the concentration of hydrogen ions (H⁺) increases, the pH value decreases (more acidic).

35
Q

How does the concentration of hydroxide ions (OH⁻) affect the pH value?

A

A: As the concentration of hydroxide ions (OH⁻) increases, the pH value increases (more alkaline).

36
Q

What are the two common methods for measuring pH?

A

A: Using a universal indicator or a pH meter.

37
Q

What does a universal indicator do?

A

A: The universal indicator changes color based on the pH value of a solution.

38
Q

What is the degree of dissociation?

A

A: The degree of dissociation, also known as the degree of ionisation, determines the strength of an acid or alkali by how much it dissociates in water.

39
Q

What is a strong acid?

A

A: A strong acid is a chemical substance that dissociates completely in water to form freely moving hydrogen ions (H⁺).

40
Q

Give examples of strong acids.

A

A: Examples include:

Hydrochloric acid (HCl)
Sulphuric acid (H₂SO₄)
Nitric acid (HNO₃)

41
Q

What is a weak acid?

A

A: A weak acid is a chemical substance that dissociates only partially in water to form hydrogen ions (H⁺).

42
Q

Give examples of weak acids.

A

A: Examples include:

Ethanoic acid (CH₃COOH)
Carbonic acid (H₂CO₃)

43
Q

What is a strong alkali?

A

A: A strong alkali is a chemical substance that dissociates completely in water to produce hydroxide ions (OH⁻).

44
Q

What is a weak alkali?

A

A: A weak alkali is a chemical substance that dissociates only partially in water to produce hydroxide ions (OH⁻).

45
Q

Give examples of weak alkalis.

A

A: Examples include:

Calcium hydroxide (Ca(OH)₂)
Aqueous ammonium (NH₄OH)

46
Q

What are the four main chemical properties of acids?

A
  1. Acids taste sour.
  2. They turn blue litmus paper red.
  3. Their pH value is less than 7.
  4. Acids are corrosive.
47
Q

What is the reaction when an acid reacts with a base?

A

It produces salt and water.
Example Reaction:
HCl(aq) + NaOH(aq) → NaCl(aq) + H₂O(l)

48
Q

What is produced when an acid reacts with a reactive metal?

A

The reaction produces salt and hydrogen gas.
Example Reaction:
2HCl(aq) + Zn(s) → ZnCl₂(aq) + H₂(g)

49
Q

What happens when an acid reacts with a metal carbonate?

A

The reaction produces salt, water, and carbon dioxide gas.
Example Reaction:
2HCl(aq) + CaCO₃(s) → CaCl₂(aq) + H₂O(l) + CO₂(g)

50
Q

What are the main properties of alkalis?

A
  1. Alkalis taste bitter and feel soapy.
  2. They turn red litmus paper blue.
  3. Their pH value is greater than 7.
  4. Alkalis react with acids to produce salt and water.
  5. When heated with ammonium salts, they produce ammonia gas.
51
Q

What is the reaction when an alkali reacts with an acid?

A

It produces salt and water.
Example Reaction:
2KOH(aq) + H₂SO₄(aq) → K₂SO₄(aq) + 2H₂O(l)

52
Q

What happens when an alkali reacts with an ammonium salt?

A

The reaction produces salt, water, and ammonia gas.
Example Reaction:
KOH(aq) + NH₄Cl(aq) → KCl(aq) + H₂O(l) + NH₃(g)

53
Q

What is the reaction of an alkali with a metal ion?

A

It produces insoluble metal hydroxide and alkali cation.
Example Reaction:
2NaOH(aq) + Mg²⁺(aq) → Mg(OH)₂(aq) + 2Na⁺(aq)

54
Q

What is the concentration of a solution?

A

A: It is the measurement of the quantity of solute dissolved in a unit volume of solution, usually in 1dm-³

55
Q

How is concentration in
𝑔dm−³ defined?

A

A: It is the mass of solute found in
1dm-³

56
Q

What is the formula for concentration in 𝑔dm−³

A

Concentration(gdm-³)
= Massofsolute(g) /
Volumeofsolution(dm³)

57
Q

How is concentration in
mol dm−³ defined?

A

A: It is the number of moles of solute found in 1dm−³ of solution.
This is called molarity.

58
Q

What is the formula for concentration in mol dm−³

A

Concentration(moldm−³)
= Numberofmolesofsolute(mol)/
Volumeofsolution(dm³)

59
Q

What two factors affect the pH value of an acidic or alkaline solution?

A

Degree of dissociation
Molarity or concentration

60
Q

How does the degree of dissociation affect the pH value?

A

Higher dissociation of an acid → Lower pH
Higher dissociation of an alkali → Higher pH

61
Q

How does molarity affect the pH value?

A

Higher molarity of an acid → Lower pH
Higher molarity of an alkali → Higher pH

62
Q

What is a standard solution?

A

A solution with a known concentration.

63
Q

What is the first step in preparing a standard solution from a solid?

A

A: Determine the mass of solid needed using the formula:

𝑛 = 𝑀
𝑉⋅1000

Where
𝑛 is the number of moles,
𝑀 is molarity
𝑉 is volume in cm³.

64
Q

During dilution, what changes and what remains constant?

A

A: The concentration of the solution changes, but the number of moles of solute remains constant.

65
Q

What formula is used to calculate the dilution of a solution?

A

𝑀¹𝑉¹= 𝑀²𝑉²
​
Where:
𝑀¹ : Molarity of the stock solution before dilution.
𝑉¹ : Volume of the stock solution before dilution.
𝑀² : Molarity of the solution after dilution.
𝑉² : Volume of the solution after dilution.

66
Q

What is the application of neutralisation in the industry?

A

Calcium carbonate is used to remove acidic gases, such as sulphur dioxide, before it is released into the air.

67
Q

How does neutralisation benefit health?

A

Antacids and milk of magnesia are used to neutralise excess hydrochloric acid in the stomach of gastric patients.

68
Q

Which substance is used in neutralisation for agriculture?

A

Lime or calcium carbonate.

69
Q

What role do antacids play in neutralisation?

A

They neutralise excess hydrochloric acid in the stomach.

Chemistry ✦ (Form 4) (11 decks)

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