LAB 6-2B: Factors affecting reaction rate

Purpose: 

• To observe how various factors (temperature, surface area and the presence of a catalyst) affect the rate of chemical reactions.

Materials: 

Part 1 (Temperature):  

•  Two 400 ml beaker
•  Ice water
•  Hot water
•  Thermometer
•  3 Effervescent tablets (Denture cleaners)
•  Stopwatch

Part 2 (Catalyst): 

•  3 Small test tubes 
•  Test tube rack 
•  Dish soap
•  6% Hydrogen peroxide solution (H2O2)
•  Potassium iodide (KI) 
•  Copper(II) chloride (CuCl2)
•  Sodium chloride (NaCl)

Part 3 (Surface Area):

•  Mortar and pestle 
•  Sodium carbonate 
•  4 Small test tubes 
•  Test tube rack 
•  Dilute hydrochloric acid solution (HCL)

Procedure: 

•  Refer to page 279 of textbook

Results: 

Part 1 (Temperature):

	Hot Water	Cold Water	Warm Water
Temperature	57˚C	5˚C	27˚C
Approximate time it took to dissolve	After around 3 minutes about half of the effervescent tablet was dissolved, therefore we can estimate that it would have taken approximately 6 minutes for it to completely dissolve.	After around 8 minutes about half of the effervescent tablet was dissolved, therefore we can estimate that it would have taken approximately 16 minutes for it to completely dissolve.	After around 5 minutes about half of the effervescent tablet was dissolved, therefore we can estimate that it would have taken approximately 10 minutes for it to completely dissolve. I originally estimated around 11 minutes

Part 2 (Catalyst):

Fast	KI (Potassium iodide): This compound produced the most foam in the shortest period of time. The solution was yellowy orange in color. It eventually overflowed out of the tube. Thus it was the most reactive out of the three.
Medium	CuCl2 (Copper II chloride): This compound also produced foam although less than the potassium iodide it reacted fairly quickly. The solution was bluish green in color and the compound in the middle of the three.
Slow	NaCl (Sodium chloride): There was almost no foam and not a significantly visible reaction.  There was slight bubbling and fizzing. The solution was clear and the compound with the slowest reaction rate between the three.

Part 3 (Surface area): 

	Result:
Sodium sulphate lumps	Instantly fizzed but then settled, there were bubbles that continuously rose but then stopped anticlimactically.
Powdered sodium sulphate	Instantly fizzed but less dramatically than the lumps towards the beginning. Once stirred the reaction seemed to be faster compared to the lumps but then settled again towards the bottom.

Discussion:

Analyse

     1. What is the relationship between rate of reaction and change in temperature?

• The relationship between the rate of reaction and change in temperature is that the reaction rate will become faster if the temperature is higher and slower if the temperature is lower. This is due to kinetic molecular theory, if the temperature is higher the molecules move faster causing more collisions which results in a faster rate of reaction.

    2. Compare your prediction in step 4 of the length of time it would take an effervescent tablet to dissolve at middle temperature with how long it actually took.

• Through the results from the hot and cold water I predicted it to take around 11 or 12 minutes for the effervescent tablet in middle temperature water to completely dissolve. In reality during our experiment we estimated it to have taken around 10 minutes.

      3. 

       a) Which of the solutions that were added to the hydrogen peroxide solution may have acted as a catalyst?

• Because there was the same hydrogen peroxide and dish soap put in all three test tubes the only different factor among them were the solutions placed in to them which were all ionic. They all reacted although at different rates therefore they were all catalysts.

   b) Which catalyst sped up the reaction the most?

• Potassium Iodide was the catalyst which sped up the reaction the most.

     4. Which has more surface area, a 5g lump of sodium carbonate or 5g of sodium carbonate powder?

• We know that the 5g of sodium carbonate powder has more surface area because it is the same thing but crushed up therefore making more surface area and more surface for the molecules to hit as opposed to a lump where there is less surface area exposed.

     5. How did the surface area affect the rate of sodium carbonate 

decomposition in step 14?

• In this experiment at first the surface area didn't make much of a difference, in fact the lump reacted faster than the powder. However after we mixed the test tube containing the powder it reacted somewhat faster but it wasn't a drastic change. When surface area is increased, it allows for the dilute hydrochloric acid molecules to collide with more sodium carbonate atoms at a time, rather than only coming in contact with the atoms on the surface.

Conclude and Apply

     1. Suppose a reaction involved a finely ground powder reacting with a concentrated acid. Suggest three methods of decreasing the reaction rate.

• To decrease the reaction rate of a reaction involving a powder and a concentrated acid we could do multiple things. Firstly we could decrease the temperature of the acid causing the molecules within to slow down. Another way to decrease the reaction rate is to substitute the finely ground powder with a lump so that there is less surface area to react on and lastly we could refrain from using a catalyst which would slow down the reaction significantly.

Conclusion

• In conclusion through this experiment I was able to observe how temperature, surface area and the presence of a catalyst will significantly alter the rate of a reaction. I have now witnessed that the higher the temperature, the larger the surface area and the presence of a catalyst all contribute to a faster chemical reaction. Although all the experiments went well and we acquired accurate information we could have done part 3 in a better way to receive more prominent results. We should have used less powder and possibly even smaller lumps of sodium sulphate to make the results more obvious to the eye. All in all I really enjoyed this experiment and it has given me valuable knowledge that will help me aspire to my academically science-based future.