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Chemistry A2 UNIT 5 > ISA > Flashcards

ISA Flashcards

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1
Q

What is the independent variable?

A

The conc. of iodide ions.

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2
Q

What is the rate equation?

A

Rate=k[A]^m[B]^n

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3
Q

What does the order of reaction mean?

A

0- [A] changes and rate stays the same
1- Rate is proportional to [A]
2- Rate is proportional to [A]^2

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4
Q

What doe a bigger rate constant mean?

A

faster rate of reaction

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5
Q

When is k the same?

A

For a particular reaction at a particular temperature

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6
Q

What does increasing the temperature of a reaction do?

A

Increases rate of reaction because number of collisions increases, as well as the energy of each collision.

Conc. of reactants and orders of reaction stay the same so k must increase for rate equation to balance.

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7
Q

RATE OF REACTION

A

The change in the amount of reactants or products per unit of time

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8
Q

How do you work out gradient?

A

change in y/change in x

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9
Q

What is gradient?

A

order of reaction

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10
Q

What is the rate determining step?

A

Slowest step in a multi step reaction.

If a reactant occurs in the rate equation, it must affect the rate.

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11
Q

How do you work out % yield?

A

actual yield/theoretical yield X 100

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12
Q

How do you work out theoretical yield?

A

Moles of reactant to moles of desired product (ratio)

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13
Q

What is a variable?

A

Quantity that has the potential to change.

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14
Q

DISCRETE DATA

A

Counting (eg bubbles)

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15
Q

CONTINUOUS

A

any value in a scale

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16
Q

What are scatter plots good for?

A

Showing how two sets of data are related.

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17
Q

VALID RESULTS

A

Answer original question, fair test

18
Q

ACCURATE RESULTS

A

Close to true value

19
Q

PRECISE

A

Using sensitive instruments that measure in small increments

20
Q

RELIABLE

A

Consistently reproduced.

21
Q

Why is ethanoic anhydride over ethanoyl chloride?

A

Cheaper,
Safer as do not get HCl gas produced
HCl(g) dissolves in water and becomes corrosive.
Reacts more slowly

22
Q

What is Carbon NMR?

A

Tells you how many different carbon environments a molecule has.

23
Q

Describe NMR

A

Any atomic nucleus with an odd number of nucleons in its nucleus has a nuclear spin. This causes a weak magnetic field.
NMR spectroscopy looks at how small magnetic field reacts when you put in a much larger external magnetic field.

24
Q

Where do sources of error come from (from experiment)?

A
  • Glasswear error
  • Not done under standard conditions - temperature fluctuations prevented by being in a thermostatically controlled water bath
  • Timing error- longer time stirring is more accurate.
25
Q

What was the dependent variable?

A

Time taken for formation of blue black colour.

26
Q

What were the controlled variables?

A

Conc and volume of sodium thiosulphate
conc. an vol . of starch.
conc and vol of hydrogen peroxide.

27
Q

% error

A

(your result- accepted value)/accepted value X 100

28
Q

How is the purity of a product determined by recrystallisation?

A

Solid dissolved in a minimum volume of hot solvent and any impurities are removed by filtration of hot solution.
Unwanted colouring matter may be removed by heating solution with charcoal- absorbs coloured material.
Hot solution allowed to cool slowly to enable crystallisation to occur. Soluble impurities should remain in solution.
Crystals filtered using Buchner funnel, washed with cold solvent and dried.

29
Q

How do you determine the purity of a solid using melting point?

A

Melting point range is very narrow for pure solids, the presence of even a small amount of impurity will lower a compound’s melting point by a few degrees and broaden melting point temperature range.

Impurity causes defects in crystalline lattice, easier to overcome the intermolecular interactions between the molecules.

30
Q

Why might the % yield not be 100%?

A
  • Reaction might not be 100% completed because it is reversible and an equilibrium is established.
  • Always get losses of the desired product as it is separated from the reaction mixture
  • Some reactants may react in a different way to give a different product that the one you want.
31
Q

What are the reactants an products in making aspirin?

A 
REACTANTS
2-hydroxy benzene carboxylic acid
Ethanoic anhydride
PRODUCTS
Aspirin
ethanoic acid
32
Q

Why is the minimum amount of hot solvent used?

A

Get the most product at the end, don’t want any left in solution.

33
Q

Why don’t impurities crystallise?

A

There is not enough

34
Q

Why does the solution need to cool slowly?

A

Larger crystals made.

35
Q

How are the crystals filtered?

A

Filter pure product under reduced pressure using a Buchner funnel and side arm hook.

36
Q

Describe the process of purity determination.

A
  • Strap capillary tube to a thermometer.
  • Sit in oil bath- higher boiling point than water
  • heat gently
  • when it melts it goes transparent
  • Note melting point when first starts to melt and when all has melted.
  • If it has a narrow range of melting point it is more pure.
  • Use data book to match known melting point.
37
Q

Why is the reaction with ethanoyl chloride faster?

A

More reactive

38
Q

Why is % yield of recrystallisation not 100%?

A
  • Not all product crystallised out during recrystallisation, some stays in solution and not trapped in filter paper.
  • Some crystal product left in boiling tube or beaker and not transferred into Buchner funnel.
  • Product may not have been fully dry when weighed for % yield.
39
Q

Why is a filter seal essential in a Buchner funnel?

A

Achieve good suction.

40
Q

Why is it essential to connect a Buchner funnel to a vacuum pump via a trap?

A

To prevent suck back of water.

41
Q

What is the order of reaction with respect to iodide ions?

A

1

42
Q

How do you work out % error in glasswear?

A

tolerance/volume measured X 100

Chemistry A2 UNIT 5 (5 decks)

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