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DATCrusher Chem Videos > Chemistry Video 14 > Flashcards

Chemistry Video 14 Flashcards

1
Q

Dynamic equilibrium

A

Rates of forward and reverse reactions are equal. Appears as though there is no activity. Can also occur for phase changes.

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2
Q

Reaction quotient

A

Q = ([C]^x [D]^y) / ([A]^m [B]^n). Where C and D are products. A and B are reactants. x, y, m and n are the respective stoichiometric coefficients in the reaction. At the start of any reaction, Q = 0. As the reaction proceeds, Q will also increase as products are formed. Contains only aqueous or gaseous species. Q or Qc varies and is non-constant.

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3
Q

Q = K

A

Occurs at equilibrium. Q is constant because concentrations become constant at equilibrium. The equilibrium constant K is Kc and is the same as the reaction quotient. Kc is a constant value. Contains only aqueous or gaseous species.

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4
Q

Kc tells us where the equilibrium is

A

Kc&raquo_space; 1, means that products dominate. Kc &laquo_space;1, means that reactants dominate.

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5
Q

Q > K

A

equilibrium shifts left, reverse reaction favoured

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6
Q

Q < K

A

equilibrium shifts right, forward reaction favoured

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7
Q

Le Chatelier’s Principle

A

If a system at equilibrium experiences a stress, it will move in a direction to relieve that stress and return to equilibrium.

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8
Q

Types of stress

A
  1. Change in concentration.
  2. Change in pressure; if the pressure increases (or volume decreases), the reaction favours the side of the equation with fewer moles of gas to reduce excess pressure. If the pressure decreases (or volume increases), the reaction favours the side with more moles of gas to restore the lost pressure. A change only occurs if the number of gaseous particles is different on both sides of the reaction.
  3. Change in temperature; This changes the value of K (equilibrium constant). Exothermic means that heat is product. Endothermic means that heat is reactant
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9
Q

ICE table

A

Used for equilibrium calculations!! Practise this.

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10
Q

Bronsted-Lowry Acid

A

donates a proton

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11
Q

Bronsted-Lowry Base

A

accepts a proton

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12
Q

Conjugate base

A

acid that lost its proton. Has a charge that is 1 less than the charge of its acid. The more stable the conjugate base, the stronger the acid.

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13
Q

Conjugate acid

A

base that accepted a proton. Has a charge that is 1 more than the charge of its base

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14
Q

List of strong acids

A 
Hydrochloric acid (HCl)
Hydrobromic acid (HBr)
Hydroiodic acid or hydriodic acid (HI)
Sulfuric acid (H2SO4)
Nitric acid (HNO3)
Chloric acid (HClO3)
Perchloric acid (HClO4)
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15
Q

List of strong bases

A 
LiOH - lithium hydroxide.
NaOH - sodium hydroxide.
KOH - potassium hydroxide.
RbOH - rubidium hydroxide.
CsOH - cesium hydroxide.
*Ca(OH)2 - calcium hydroxide.
*Sr(OH)2 - strontium hydroxide.
*Ba(OH)2 - barium hydroxide.
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16
Q

Amphoteric

A

Can act as acid or base. i.e. water

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17
Q

Lewis acid

A

electron pair acceptor

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18
Q

Lewis base

A

electron pair donor

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19
Q

Acid dissociation constant

A

Ka = ([A-]*[H3O+]) / [HA]. Large Ka means stronger acid, favouring products. Small Ka means weaker acid, favouring reactants.

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20
Q

Base dissociation constant

A

Kb = ([BH+]*[OH-]) / [B]

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21
Q

pH

A

pH = -log[H3O+]. [H3O+] = 10^(-pH)

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22
Q

Acid strength trends

A

Referring to central atom of acid:

  1. Acidity increases going down the periodic table. Larger anions can better accommodate the negative charge when an acid ionizes. i.e. HF < HCl < HBr < HI
  2. Acidity increases going to the right of the period on periodic table. More electronegative atoms can accommodate negative charge. i.e. CH4 < NH3 < H2O < HF
23
Q

Base strength trends

A

Basicity of central atom increases going up and left on periodic table. Opposite trend to acid trends. More electropositive atoms can better accommodate positive charges.

24
Q

Acid or base strength in molecules with hydroxyl group OH

A

Can be acidic, basic or amphoteric, depending on nature of the central atom. If central atom has low electronegativity, OH- is produced, meaning that the molecule was a base. If central atom has high electronegativity, H3O+ is produced, meaning that the molecule was an acid (These are oxyacids).

25
Q

Oxyacid

A

An acid that contains oxygen. Strength of oxyacid increases as electronegativity of central atom increases. Strenght of oxyacid also increases as oxidation number of central atom increases. i.e. HNO3 has N with +5 so it is stronger acid than HNO2 where N is +3

26
Q

Autoionization of water

A

Water can react with itself. H2O + H2O < > HO- + H3O+. This is an acid-base equilibrium with an equilibrium constant of Kw

27
Q

Kw

A

Kw = [HO-]*[H3O+] = 1.0 * 10^(-14) at 25 degrees Celsius. The Kw value increases as temperature increases. In the Kw expression, [HO-] = [H3O+] = 1.0 * 10^(-7) at 25 degrees Celsius. Kw = [HO-]^2 = [H3O+]^2

28
Q

pOH equation

A

pOH = -log[OH-].

29
Q

[OH-] concentration equation

A

[OH-] = 10^(-pOH)

30
Q

pH + pOH

A

pH + pOH = 14

31
Q

Neutral solution

A

Occurs when [OH-] = [H3O+]. i.e. water. Occurs when you react strong base with strong acid.

32
Q

Neutralization reactions

A

Acid and base reacting together. Resulting solution depends on relative strength of acid and base. Must produce water.

33
Q

Strong acid + strong base

A

Resulting solution has water and ionic salt. Forms neutral solution where [OH-] = [H3O+]. Also depends on stoichiometric amount of the strong acid and strong base. We need equimolar quantity of H from strong acid and OH from strong base to form neutral solution.

34
Q

Strong acid + weak base

A

Resulting solution is slightly acidic.

35
Q

Weak acid + strong base

A

Resulting solution is slightly basic.

36
Q

Weak acid + weak base

A

Hard to predict. Resulting solution may be acidic, neutral or basic

37
Q

Buffer

A

Mixture of weak acid or weak base with its conjugate. The solution can resist changes in pH when small amounts of an acid or base is added. i.e. CH3COOH (weak acid) + CH3COO- (conjugate base). i.e. NH3 (weak base) + NH4+ (conjugate acid). One proton separates the molecules in the pair. i.e. An equation may be CH3COOH + H2O < > CH3COO- + H3O+

38
Q

Buffer capacity

A

Amount of acid or base that can be added to a certain volume of the buffer solution before the pH changes significantly (> 1 pH unit). Depends on amount of acid and base in solution; Greater amount is greater buffer capacity.

39
Q

Henderson-Hasselbalch Equation

A

pH = pKa + log ([A-] / [HA]). For buffer solutions, usually [A-] = [HA], which means that the equation can be simplified to end in “log1”. Log1 is equal to 0. The equation is further simplified to pH = pKa. Thus, when preparing a buffer solution using equal amounts of acid and base, then the pH of the solution will be equal to the pKa of the acid.

40
Q

Titration

A

Allows for determination of concentration of an acid or base. Neutralization reaction is monitored with coloured indicator

41
Q

Equivalence point

A

Precisely enough base to neutralize all the acid. There is no acid or base

42
Q

Titration graph trends for different acid and base strengths

A

The behaviour of the curve approaching the equivalence point is different for different acid and base strengths. But, the behaviour of the curve is the same after the equivalent point for different acid and base strengths

43
Q

Strong acid and strong base titration

A

Equivalence point pH = 7. Before the equivalence point, the curve is a wide “U”. After the equivalence point, the curve is an even wider upside down “U”

44
Q

Weak acid and strong base titration

A

Equivalence point pH > 7. Before the equivalence point, the curve is a wide upside down “U” and then a wide right-side up “U”. After the equivalence point, the curve is an even wider upside down “U”

45
Q

Acid-base indicator

A

gives visual indication of when a stoichiometric amount of acid or base has precisely neutralized the analyte. i.e. phenolphthalein is colourless when [H3O+] > 510^(-9) M or when pH < 8.3. Phenolphthalein is bright pink when [H3O+] < 510^(-9) M or when pH > 8.3. Any indicator has a colour change interval, which is a span of 1-2 units; it depends on pKa of the indicator. Phenolphthalein has colour change interval between 8 and 10.

46
Q

Analyte

A

Substance of unknown concentration but known volume. Placed in flask

47
Q

Titrant

A

Substance of known concentration but known volume. Placed in burette

48
Q

Solubility product constant, Ksp

A

Degree to which a substance dissolves. Composed of concentrations of products raised to the power of their stoichiometric coefficients. Do not include solid molecules. Smaller Ksp means lower solubility

49
Q

Common ion effect

A

The decrease in solubility of an ionic precipitate by the addition to the solution of a soluble compound with an ion in common with the precipitate. This behaviour is a consequence of Le Chatelier’s principle. Presence of ‘compound that dissociates into ions where one ion is the same as the ion in the original solution’ will promote precipitation. In calculation, may ignore an “x” because the value is very small and negligible

50
Q

Q > Ksp

A

Precipitate forms

51
Q

Q < Ksp

A

Precipitate does not form

52
Q

Half-equivalence point

A

pH = pKa because concentration of acid and concentration of conjugate base are the same

53
Q

Second equivalence point

A

Occurs with diprotic acids or bases (Can donate or accept more than 1 proton)

DATCrusher Chem Videos (17 decks)

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