1.1.1 - Laboratory Activity : Measuring Rate of Reaction

Laboratory Activity 1.1.1: Measuring Rate of Reaction

Aim: To determine the rate of reaction between hydrochloric acid (HCl) and zinc (Zn).
Problem statement: How to differentiate between instantaneous rate of reaction and average rate of reaction?
Hypothesis: The instantaneous rate of reaction are not the same as the average rate of reaction.
Variable:

	»	Fixed variable : Physical condition of the experiment
	»	Manipulated variable : Time
	»	Responding variable : Volume of hydrogen gas released

Material: » Zinc pallet » Water » Hydrochloric acid 0.5mol dm-3

Apparatus: » Conical flask » Delivery tube » Burette » Stopwatch » Retort stand with clamp

Procedure:

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	►	1. 25cm3 of hydrochloric acid, 0.5mol dm-3 is measured with a measuring cylinder and poured into a conical flask. 2. A burette full of water is inverted in a basin of water and then clamped vertically with a retort stand. 3. 5g of zinc pallet is put into the conical flask which containing hydrochloric acid. 4. The delivery tube is connected to conical flask, channeling the released gas into the burette. 5. The stopwatch is started immediately. 6. The volume of the gas released into the burette is recorded every 30 second. 7. The conical flask is swirl constantly throughout the experiment.

Data:

Time/second	Burette reading/cm3	Volume of gas/cm3
0	50	0
30	40	10
60	32	19
90	23	27
120	17	33
150	12	38
180	8	42
210	5	45
240	3	47
270	2	48
300	2	48
330	2	48
360	2	48
390	2	48

Graph and calculation:

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	►	Average rate of reaction: Total volume of gas released = 48cm3 Total time taken = 270 seconds $\text{Average rate}\mathrm{=}\frac{\mathrm{Total\; volume\; of\; gas\; released}}{\mathrm{Time\; interval}}$ $\mathrm{=}\frac{48{\text{cm}}^3}{\mathrm{270s}}$ = 0.178cm3s-1
	►	Instantaneous rate at 90 seconds ( A tangent was drawn at the 90 seconds gradient) $\mathrm{=}\frac{40–13{\mathit{cm}}^3}{150\mathrm{-}30s}$ = 0.225cm3s-1

Discussion:

	►	For all chemical reactions, the initial reaction is at the higher rate (base on the vertical gradient of the graph).
	►	The rate of reaction decreases as time elapses.
	►	The average rate based on this experiment is 0.178cm3s-1

Conclusion:

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The average rate of reaction is different from the instantaneous rate of reaction.

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