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Chemistry - A Level > O Last Minutes > Flashcards

O Last Minutes Flashcards

1
Q

What is meant by a weak acid and bronsted Lowry theory?

A

Proton donor which which partially dissociates

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2
Q

Write the full equation for the reaction of C2H5COOH with sodium carbonate

A

C2H5COOH + Na2CO3 -> C2H5COONa + CO2 + H2O

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3
Q

Write the ionic equation for an acid + a hydroxide

A

H+ + OH- -> H2O

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4
Q

Explain in terms of equilibrium how the buffer solution would respond to the added NH3

A

NH3 is a base
So equilibrium shifts right
Alkali accepts H+

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5
Q

What is acid 2 usually?

A

The + ion

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6
Q

CH3COOH + H2O = ??

A

CH3COO- + H3O+

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7
Q

How can an aqueous solution of an acid contain hydroxide ions?

A

Water ionises
H2O -> H+ + OH-

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8
Q

How do you calculate the concentration of hydroxide ions?

A

Use Kw

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9
Q

Acid + carbonate ->?

A

Salt + CO2 + H2O

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10
Q
A

Because solution contains CH3COOH and CH3COO-

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11
Q
A
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12
Q

Acid + metal ionic equation

A

M + H+ -> M+ + H2

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13
Q

Ionic equation for acid + carbonate

A
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14
Q

Explain why a buffer solution forms when butanoic acid is added to sodium hydroxide?

A

CH3CH2CH2COO- forms
CH3CH2CH2CooH remains in excess

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15
Q

What is meant by the strength of an acid?

A

The proportion of dissociation

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16
Q

What does low pKa mean?

A

Low pH and strong acid

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17
Q

equation for acid + hydroxide

A

Salt + water

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18
Q

What do you do when there are 2 OH- ions?

A

Multiply the OH- conc by 2 when working out H+

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19
Q

What important factor does the student need to consider when deciding on the most suitable indicator for this titration?

A

The colour change of the indicator

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20
Q

Equation for the percentage molar dissociation

A
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21
Q

How do we know if a reaction is endothermic using Kw?

A

Endothermic because Kw increases with temperature

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22
Q

What is wring with using Kw?

A

Inaccurate results because Kw values with temperature

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23
Q

Plan an experiment that a student could carry out to measure the enthalpy change of neutralisation

A

Acid and alkali mix
Amount of acid and alkali stated
Temp taken at start and finish
Q = MCT
Energy scaled up from 1 mol of water
Hneut = - energy change

24
Q

Suggest reasons for the difference between the enthalpy changes of solution of KF and RbF (KF has a smaller enthalpy change)

A

Ionic radius of K ion is smaller than
K+ has greater attraction
K+ has greater attraction to H2O
Enthalpy change of solution is affected more by LE than enthalpy change of hydration

25
Q

Explain why ammonium nitrate in the cold pack dissolves spontaneously in water even though this process is endothermic.

A

Entropy increases
Total entropy change > change in enthalpy

26
Q

Explain, with the help of an appropriate equation, how this buffer solution works when acid is added.

A

H+ moves equilibrium to the left
To maintain pH
Excess of salt ions

27
Q

What else can [H+] be?

A

Moles of H

28
Q

Describe what the students do and the measurements they make so that they can calculate the enthalpy change of solution.

A

Place known volume of water in a beaker
Add a known mass of solid
Add solid to water while stirring
Measure temp of water before and after

29
Q

Percentage uncertainty for equipment

A

( Uncertainty x 2 / value ) X 100

30
Q

Explain how an increase in the concentration of a greenhouse gas leads to an enhanced greenhouse effect.

A

Greenhouse gases absorb IR from Earth
So more IR would be absorbed

31
Q

Describe the evidence for the relationship between the increased concentration of greenhouse gases and global warming.

A

There is a relationship between gas concentrations and temperature

32
Q

Explain how greenhouse gas molecules are involved in the process of energy transfer that start with UV radiation from the sun and result in warming of teh troposphere

A
  • Earth absorbs UV
  • Earth emits IR
  • Greenhouse gas molecules absorb IR
  • Bonds vibrate
  • KE becomes thermal energy
  • and causes Earth’s temperature to rise
33
Q

Write an equation for the reaction of ethanoic acid in water.

A

CH3COOH = CH3COO- + H+

34
Q

i. Explain why the student decided to use a pH meter rather than universal indicator to determine the pH of the solution as the titration progressed.

A

Difficult to match colour with exact pH value using UI solution

35
Q

Explain how a pH meter is calibrated

A

Use two buffer solutions of known pH

36
Q

What is the unit for enthalpy during an entropy equation?

A

J

37
Q

Which is the conjugate acid and which is the conjugate base?

A
38
Q

What is [A-]/[HA] equal to?

A

Ka/[H+]

39
Q

Explain why many ionic substances are soluble in water, naming the bonds which are made and broken

A

Ionic bonds are broken
Ion dipole bonds are formed
Hydrogen bonds in water are broken
Similar strength bonds are broken and made

40
Q

Why is entropy of system negative?

A

Fewer moles on RHS
So less disorder

41
Q

Explain the effect of raising the temp on the forward reaction

A

It would make entropy smaller
As the reaction would be less likely to occur

42
Q

What should you always add to a question on how a buffer solution works?

A

And there’s a large conc of the negative salt ion
Eg HCO3-

43
Q

What must you include in the equation for the ionisation of an acid?

A

reversible reaction sign

44
Q

Draw a diagram of hydrogen bonding between two water molecules

A
45
Q

Why can’t a weak acid act as a buffer?

A

No excess of A- ions
No equilibrium

46
Q

Draw an enthalpy profile diagram for a soluble salt

A
47
Q

Draw an enthalpy profile diagram for an insoluble salt

A
48
Q

Why do ionic substances not dissolve in non-polar solvents?

A
  • They do not have regions of psoitive and negative charge
  • so do not interact strongly with ions
  • Solution H is a large positive value and so dissolving is unlikely to occur
49
Q

Equation for enthalpy change of solution

A

ΔHsol = ΔHhyd (cation) + ΔHhyd (anion) - ΔHLE

50
Q

What is the equivalence point?

A

The centre of the vertical section of the titration curve

51
Q

What indicator for an acid?

A

Methyl orange

52
Q

What indicator for a base?

A

Phenolphthalein

53
Q

Suggest, with reference to the pH curve on page 4, and the information in the table above, which indicator would be suitable for this titration.

A

Phenoplthalein as equivalence points are in alkaline conditions
Methyl orange would have already changed colour

54
Q

Use ideas of inter-molecular forces to explain why carbon dioxide is only slightly
soluble in water, whereas sodium hydrogencarbonate (containing HCO3– ) is very
soluble

A

CO2 has IDIDBs between molecules
CO2 forms hydrogen bonds with water
Ions form ion dipole bonds with water
Water forms hydrogen bond with itself

55
Q

The dissolving of sodium hydrogencarbonate is an endothermic process. What can you say about the sign and magnitude of the system entropy for this process?
Explain your answer.

A

Total entropy must be positive for process to occur
System entropy must be positive and greater than surrounding entropy

56
Q

What does it mean if the calculated Ksp is > than Ksp?

A

The product made from the reactants will precipitate out of the solution as it is in excess

57
Q

How do we know if a reaction is feasible?

A

Total S is positive

Chemistry - A Level (21 decks)

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