1.2.1 - Laboratory Activity: The Effect of Surface Area on the Rate of Reaction

Laboratory Activity 1.2.1: The Effect of Surface Area on the Rate of Reaction

Aim: To show the effect of surface area on the rate of reaction.
Problem statement: How does the total surface area of reactants affect the rate of reaction?
Hypothesis: The bigger surface area of the reactants are exposed, the higher the rate of reaction.
Variable:

	»	Fixed variable : Temperature and the quantity of the reactants
	»	Manipulated variable : Size of the reactants
	»	Responding variable : Rate of reaction

Material: » Calcium carbonate chips » Calcium carbonate powder » Hydrochloric acid 0.2mol dm-3

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

Procedure:

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	►	1. A burette full of water is inverted in a basin of water and then clamped vertically with a retort stand. 2. The water level in the burette is adjusted so that the volume of water can be read and the initial burette reading is recorded. 3. 5g of calcium carbonate chips is weighed and put inside a conical flask. 4. 50cm3 of hydrochloric acid, 0.2mol dm-3 is measured with a measuring cylinder and poured it into a conical flask. 5. The hydrochloric acid is poured inside the conical flask containing calcium carbonate chips and close immediately with the delivery tube. 6. A stopwatch is start immediately. 7. The conical flask is swirl slowly and the volume of the gas liberated is noted and recorded every 30 seconds. 8. The experiment is repeated by replacing the calcium carbonate chips with 5g of calcium carbonate powder.

Discussion:

	►	Calcium carbonate chips Time (s) Burette reading (cm3) Volume of gas (cm3) 0 50 0 30 46 4 60 42 8 90 40 10 120 37 13 150 35 15 180 33 17 210 31 19 240 29 21 270 27 23 300 25 25
	►	Calcium carbonate powder Time (s) Burette reading (cm3) Volume of gas (cm3) 0 50 0 30 40 10 60 35 15 90 31 19 120 26 24 150 23 27 180 20 30 210 17 33 240 14 36 270 12 38 300 10 40

Graph and calculation:

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	►	Average rate of reaction in 300 seconds: ○ Average rate of reaction of calcium carbonate chips = $\frac{25{\mathit{cm}}^3}{\mathrm{300s}}=0.083{\mathit{cm}}^3{s}^{-1}$ ○ Average rate of reaction of calcium carbonate powder = $\frac{42{\mathit{cm}}^3}{\mathrm{300s}}=0.14{\mathit{cm}}^3{s}^{-1}$
	►	Based on the graph, the gradient for the calcium carbonate powder is steeper compared to calcium carbonate chips. This implies that the rate of reaction for calcium carbonate powder is higher.

Discussion:

	►	Marble reacted with dilute hydrochloric acid to produce carbon dioxide, CO2, gas, as shown in the following equation: CaCO3(s) + 2HCl(aq) → CaCl2(aq) + CO2(g) + H2O(l)
	►	Calcium carbonate powder has a larger total exposed surface area compared to calcium carbonate chips. Thus, the rate of reaction for calcium carbonate powder is higher.
	►	Based on the result of the experiment, the rate of reaction decreases with time (as the graph gradient decreases with increasing time). The concentration of hydrochloric acid and the mass of calcium carbonate decrease with time.

Conclusion:

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The smaller the size of reactant, the higher the rate of reaction.

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