RP7 Flashcards

1
Q

What is meant by ‘rate of reaction’?

A

The change in concentration of reactants or products over time.

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2
Q

How can rate of reaction be measured?

A

● Initial rates method- i.e. the iodine clock reaction
● A continuous monitoring method- i.e. measuring the volume of gas released in a reaction over time.

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3
Q

What is an initial rates method?

A

The method involves measuring the initial rate of reaction for multiple different concentrations to observe how rate of reaction varies.

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4
Q

Give an example of an initial rates method.

A

● The ‘Iodine Clock’ experiment:
○ H O
2 2(aq)
+ 2H+ + 2I– (aq) (aq)
→ I + 2H O
○ 2S O 2–
2 3 (aq)
→ 2I– (aq)
2(aq)
+ S O 2–
2 (l)
+ I
● The I2 produced reacts with all of the thiosulfate ions present.
Excess I2 remains in solution which then reacts with starch to
form a blue-black solution.
● Time how long it takes for this blue-black colour to appear. You
can vary [I-] to then determine the order with respect to the iodide ions.

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5
Q

What are the issues with this experiment?

A

● Some low I- concentrations may take too long to react.
● Delayed stopwatch reactions.
● Concentrations may not be exact due
to measuring apparatus.

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6
Q

What is a continuous monitoring method?

A

This involves measuring the change in concentration of a reactant or product over time (or measuring volume of gas released) as the reaction progresses.

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7
Q

Give an example of a continuous monitoring method.

A

● Add a 6 cm strip of magnesium ribbon into a conical flask containing HCl, place a bung in the top of the flask and start the timer.
● Note down the volume of hydrogen gas collected every 15 seconds for a period of 2.5 minutes.
● Repeat for different HCl concentrations.

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8
Q

What should the set up for this experiment look like?

A

check

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8
Q

How would you analyse the data from this experiment?

A

● Plot a graph of volume of hydrogen gas produced (y-axis) against time (x-axis) for each concentration of HCl. Draw a line of best fit.
● Draw a tangent at t = 0s for each line.
● To deduce the rate of each reaction, calculate the gradient
of each tangent.
● Compare the calculated rate values.

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9
Q

What are some issues with this experiment?

A

● Some gas may escape before the bung is added.
● The magnesium strips may be of different mass and surface area etc. which will affect the rate of reaction.

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10
Q

How do you prevent gas escaping?

A

Place the solid reactant upright inside a sample tube in the conical flask, tipping the tube over by moving the conical flask around to start the reaction.

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