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chemistry - unit 2.1 Flashcards

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1
Q

When is a chemical reaction in equilibrium?

A

When the composition of the reactants and products remains constant indefinitely.

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2
Q

What does the equilibrium constant (K) characterise?

A

The equilibrium composition of the reaction mixture.

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3
Q

What does the value of an equilibrium constant indicate?

A

The position of equilibrium.

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4
Q

What units does an equilibrium constant have?

A

No units.

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5
Q

What are the concentration of pure solids and pure liquids at equilibrium taken as?

A

Constant and given a value of 1 in the equilibrium expression.

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6
Q

What does the numerical value of the equilibrium constant depend on?

A

The reaction temperature and is independent of concentration and/ or pressure.

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7
Q

For endothermic reactions, what does a rise in temperature cause?

A

An increase in K and the yield of the product is increased.

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8
Q

For exothermic reactions, what does a rise in temperature cause?

A

A decrease in K and the yield of the product is decreased.

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9
Q

What does the presence of a catalyst do?

A

It does not affect the value of the equilibrium constant.

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10
Q

In water and aqueous solutions, where is there an equilibrium?

A

Between the water molecules and hydronium and hydroxide ions.

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11
Q

How can this ionisation of water be represented by?

A

H2O(l) + H2O(l ) -> H3O+ (aq) + OH− (aq)

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12
Q

What does H3O+(aq) represent?

A

A hydronium ion, a hydrated proton. A shorthand representation of H3O+ (aq) is H+ (aq).

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13
Q

What is water?

A

Amphoteric (can react as an acid and a base).

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14
Q

What is the dissociation constant for the ionisation of water known as the ionic product, Kw?

A

Kw = [H3O+][OH-]

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15
Q

What does the value of the ionic product vary with?

A

Temperature.

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16
Q

At 25°C, what is the value of Kw?

A

approximately 1 × 10-14.

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17
Q

What is the relationship between pH and the hydrogen ion concentration given by?

A

pH=−log[H3O+] and [H3O+] = 10−pH

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18
Q

In water and aqueous solutions with a pH value of 7, what are the concentrations of H3O+ (aq) and OH− (aq)?

A

They are both 10-7 mol l-1 at 25°C.

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19
Q

If the concentration of H3O+ (aq) or the concentration of OH− (aq) is known, what can be calculated?

A

The concentration of the other ion using
Kw or by using pH + pOH = 14 .

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20
Q

What is the Brønsted-Lowry definition of an acid?

A

A proton donor.

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21
Q

What is the Brønsted-Lowry definition of a base?

A

A proton acceptor.

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22
Q

For every acid, what is there?

A

A conjugate base, formed by the loss of a proton.

23
Q

For every base, what is there?

A

A conjugate acid, formed by the gain of a proton.

24
Q

What are strong acids and strong bases?

A

Completely dissociated into ions in aqueous solution.

25
Q

What are weak acids and weak bases?

A

Only partially dissociated into ions in aqueous solution.

26
Q

What are examples of strong acids?

A

Hydrochloric acid, sulfuric acid and nitric acid.

27
Q

What are examples of weak acids?

A

Ethanoic acid, carbonic acid and sulphurous acid.

28
Q

What are strong bases?

A

Solutions of metal hydroxides.

29
Q

What are examples of weak bases?

A

Ammonia and amines.

30
Q

What can the weakly acidic nature of solutions of carboxylic acids, sulfur dioxide and carbon dioxide be explained by?

A

Reference to equations showing the equilibria.

31
Q

What can the weakly alkaline nature of a solution of ammonia or amines be explained by?

A

Reference to an equation showing the equilibrium.

32
Q

What do equimolar solutions of weak and strong acids (or bases) have?

A

Different pH values, conductivity, and reaction rates, but the stoichiometry of reactions are the same.

33
Q

What is the acid dissociation constant represented by Ka?

A

[H3O+][A-] / [HA]
or
pKa where pKa =−log10(Ka)

34
Q

How can the approximate pH of a weak acid be calculated?

A

Using pH=1/2pKa −1/2log10(c)

35
Q

What does a soluble salt of a strong acid and a strong base dissolve in water to produce?

A

A neutral solution.

36
Q

What does a soluble salt of a weak acid and a strong base dissolve in water to produce?

A

An alkaline solution.

37
Q

What does a soluble salt of a strong acid and a weak base dissolve in water to produce?

A

An acidic solution.

38
Q

What does the name of the salt produced depend on?

A

The acid and base used.

39
Q

How can the changes in concentrations of
H O+ and OH− ions of salt solutions be explained?

A

Using the appropriate equilibria.

40
Q

What is a buffer solution?

A

One in which the pH remains approximately constant when small amounts of acid, base or water are added.

41
Q

What does an acid buffer consist of?

A

A solution of a weak acid and one of its salts made from a strong base.

42
Q

In an acid buffer solution, what does the weak acid provide?

A

Hydrogen ions when these are removed by the addition of a small amount of base.

43
Q

What does the salt of the weak acid provide, in an acid buffer?

A

The conjugate bae, which can absorb excess hydrogen ions produced by the addition of a small amount of acid.

44
Q

What does a basic buffer consist of?

A

A solution of a weak base and one of its salts.

45
Q

In a basic buffer solution, what does the weak base do?

A

It removes excess hydrogen ions.

46
Q

In a basic buffer solution, what does the conjugate acid provided by the salt do?

A

it supplies hydrogen ions when these are removed.

47
Q

How can an approximate pH of an acid buffer solution be calculated?

A

From its composition and from the acid dissociation constant:
pH = pKa − log[acid]/[salt]

48
Q

What are indicators?

A

Weak acids for which the dissociation can be represented as:
HIn(aq)+H2O(l) -> H3O(aq) + In-(aq)

49
Q

In aqueous solution, what is the colour of an acid indicator?

A

Distinctly different from that of its conjugate base.

50
Q

What is the colour of the indicator determined by?

A

The ratio of [HIn] to [In−]

51
Q

What is the theoretical point at which colour change occurs?

A

When [H3O+]=Kln.

52
Q

When is the colour change assumed to be distinguishable?

A

When [HIn] and [In−] differ by a factor of 10.

53
Q

What is the pH range over which a colour change occurs estimated by?

A

The expression:
pH = pKIn +/-1

54
Q

Where can suitable indicators be selected from?

A

pH data, including titration curves.

advanced higher chemistry (36 decks)

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