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OCR Chemistry > F325 > Flashcards

F325 Flashcards

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1
Q

What is a conjugate acid?

A

A species formed when a proton is added to a base.

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2
Q

What is the colour change for Cu2+ and OH-?

A

Blue solution to pale blue precipitate.

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3
Q

What is the colour change for Fe2+ and OH-?

A

Green solution to dark green precipitate. Turns rust coloured in air.

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4
Q

What is the colour change for Fe3+ and OH-?

A

Yellow solution to rust coloured precipitate.

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5
Q

What is the colour change for Co2+ and OH-?

A

Pink solution to blue precipitate.

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6
Q

What is the colour change for Mn2+ and OH-?

A

Pink solution to creme precipitate.

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7
Q

What is the colour change for Cu2+ and excess NH3?

A

Blue solution to pale blue precipitate, followed by dark blue solution (if ammonia is in excess).
H2O + NH3 NH4+ + OH-
The precipitate is caused by OH- ions.

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8
Q

What is the colour change for Cu2+ and concentrated HCl?

A

Blue solution to yellow solution (which looks green due to the equilibrium).

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9
Q

What is the colour change for Co2+ and concentrated HCl?

A

Pink solution to blue solution.

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10
Q

What is a buffer solution and how is it formed?

A

A system that minimises the change in pH when small amounts of acid or base are added.
It is formed from a weak acid and a salt of the weak acid.

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11
Q

What is the enthalpy change of neutralisation?

A

The enthalpy change when aqueous acid and base react to form one mole of water.

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12
Q

What are two advantages of FCVs over internal combustion powered vehicles?

A

There are less/no CO2 emissions.

Fuel cells are more efficient than internal combustion engines (heat engines).

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13
Q

Name three ways that hydrogen could be stored.

A
  1. As a liquid under pressure.
  2. Adsorbed to a surface of a solid material.
  3. Absorbed with in a solid material.
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14
Q

What are limitations of hydrogen fuel cell technology?

A

Storing and transporting hydrogen is difficult. It could be unsafe, it is expensive to develop liquid storage solutions and ad/absorbing solids have limited life cycles.

The fuel cells themselves have a limited lifetime.

Toxic chemical are used in the production of fuel cells.

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15
Q

What are limitations of a future hydrogen economy?

A

Public and political acceptance of hydrogen as a fuel.
Initial manufacture of hydrogen requires energy which may have come from fossil fuels.
A lot of new infrastructure would have to be built.

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16
Q

How does ligand substitution apply to oxygen transport in the blood.

A

O2 donates an electron pair and forms a coordinate bond with Fe2+.
When required the O2 is substituted for anther ligand, usually CO2.

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17
Q

Why is CO toxic?

A

The complex with Fe2+ and CO has a very high stability constant. This makes the CO coordinate bond very strong and less likely to break.

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18
Q

Describe the bonding in platin. How does platin treat cancer?

A

The ligands donate an electron pair and form a coordinate bond. Platin binds to DNA of cancer cells and stops the from duplicating themselves.

19
Q

Describe how a buffer solution is formed.

A

Excess weak acid reacted with a metal to form a salt of the week acid.

20
Q

Explain how buffer solutions work.

A

Add small amounts of acid: equilibrium shifts to the left.

Add small amounts of alkali: equilibrium shifts to the right.

21
Q

Describe an experiment to measure enthalpy change of neutralisation.

A
  1. React acid and alkali together. 1 molar HCl and NaOH.
  2. Record the temperature change of the solution.
  3. Q = mc/\T, where m is the mass of reactants.
  4. Energy / moles of water that would be formed.
  5. Enthalpy of neutralisation = -Q/mol (exothermic).
22
Q

What should be mentioned when comparing enthalpy of solution changes?

A
  1. Ionic radius.
  2. Which has the most exothermic lattice enthalpy.
  3. Which has the more exothermic hydration enthalpy (the one that has a stronger attraction with water).
  4. Enthalpy change of solution is more affected by lattice enthalpy than by hydration enthalpy.
23
Q

In a worded Kc question equilibrium question…

A

The change in conditions will cause the concentration of one to change more than the other.
Concentrations will increase/decrease until Kc is restored.

24
Q

Define the term order.

A

The power to which the concentration of a reactant is raised in the rate equation.

25
Q

What is the rate constant?

A

A constant that links the rate of reaction with the concentration of reactants raised to their order.

26
Q

What is the half-life of a reaction?

A

The time taken for the concentration of a reactant to reduce by half. It is independent of concentration.

27
Q

Define the R.D.S.

A

The slowest step in the mechanism of a multistage reaction.

28
Q

List what the gradient for conc-time graphs represent.

A
  1. Negative linear - zero order.
  2. Curve, constant half life - first order.
  3. Curve, stepper and non constant half life - second order.
29
Q

Describe the initial rates method for finding the order.

A
  1. Perform a series of experiments at the same temperature, changing the concentration of one reactant each time.
  2. Gradient at t = 0 of a conc-time graph shows the initial rate.
  3. Plot initial rate against conc to find the order:

Gradient = 0 - zero order.
Positive linear - first order.
Curve - second order (or higher).

30
Q

Other than the initial rates method, how can the order be found?

A

Measure the concentration of a reactant continuously as the reaction goes on and plot a conc-time graph to find the order.

31
Q

The order of a reactant can ONLY be found by experiment. What is the overall order of a reaction?

A

Overall order is the sum of individual orders.

32
Q

What is the relationship between the rate constant and temperature?

A

The rate constant increases with temperature. The relationship is NOT linear, but is a curve of increasing gradient.

33
Q

What does the acid dissociation constant show?

A

The extent of dissociation. The percentage of dissociation = 100 X [H+]/[A-].

34
Q

For a diprotic acid or dibasic base, how do you find pH?

A

-log10(2[H+]).

10^-pH = 2[H+]

35
Q

Why is water left out of equilibrium expressions?

A

The concentration of water is much greater than the concentration of ions and is considered constant.

36
Q

How do you calculate the pH of a diluted solution?

A

[H+]’ = [H+] x og volume / new volume.

37
Q

The dissociation of water is an…

A

…endothermic process because bonds are broken.

H2O H+ + OH- shifts to the right when temperature is increased.

38
Q

Explain how buffer solutions are applied to blood pH control.

A

H2CO3 H+ + HCO3-

Carbonic acid and hydrogen carbonate are used to control blood pH.

39
Q

What is the difference between a fuel cell and an electrochemical cell?

A

A fuel cell converts energy from the reaction of a fuel with oxygen into electrical energy.
An electrochemical cell can be made up of any two half cells.

40
Q

What is the reaction in an hydrogen fuel cell?

A

2H2 + O2 —-> 2H2O

41
Q

Define enthalpy change of hydration.

A

The enthalpy change when one mole of gaseous ions form one mole of aqueous ions.

42
Q

Define standard electrode potential.

A

The emf of a half cell compared with a standard hydrogen electrode in standard conditions.

43
Q

What are assumptions of the ka expression?

A

[H+] = [A-]
Some water has dissociated, but it is such a small amount that it won’t affect the pH to 2 dp.
Concentration of acid = [HA]
Since it is a weak acid, a very small percentage of the acid has dissociated.

44
Q

How is enthalpy if neutralisation calculated?

A

React equal volumes of one mol/dm3 HCl and NaOH. Record the initial temperature and the final temperature of the reaction.
Q = mc/\T where m is the mass of reactants.
/\H = Q/moles of water formed.

OCR Chemistry (3 decks)

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