Name: ______/25

INVESTIGATION #3

Examining the relationship between concentration and reaction rate

Basic Concepts

In order for a chemical reaction to occur REACTANT particles must physically come into contact with one another. Anything that increases the frequency of these encounters will increase the rate at which PRODUCTS are formed.

My predictions:

The sodium thiosulfate with ______concentration will react ______than the sodium thiosulfate with ______concentration.

Materials

·  10 mL Beaker

·  Stopwatch

·  10 mL graduated cylinder

·  Pipette containing 1M of Na2S2O3

·  Pipette containing 0.5M of HCl

·  Pipette containing distilled water

·  Sharpie/Marker

·  Blank piece of paper

Procedure

  1. On a blank piece of paper, trace the bottom of the beaker. Draw a large cross in the traced circle.
  2. Put 50 drops of Na2S2O3 in graduated cylinder, and pour into the beaker.
  3. Put 5 drops of 0.5 M HCl, pour into beaker. Swirl the beaker carefully to mix the solution, and place on the paper with the drawn cross. Begin stopwatch.
  4. Look down at the cross from above. Once the cross disappears, stop stopwatch. Record time.
  5. Clean the beaker and repeat steps 2-4 for a second trial.
  6. Calculate average reaction time for 50 drops of Na2S2O3.
  7. Measure 40 drops of Na2S2O3 and 10 drops of water in graduated cylinder; pour into the beaker.
  8. Clean the beaker and repeat steps 3 and 4.
  9. Clean the beaker and repeat steps 7, 3 and 4 for a second trial.
  10. Calculate average reaction time for 40 drops of Na2S2O3
  11. Measure 20 drops of Na2S2O3 and 30 drops of water in graduated cylinder; pour into the beaker.
  12. Clean the beaker and repeat steps 3 and 4.
  13. Clean the beaker and repeat steps 11, 3 and 4 for a second trial.
  14. Calculate average reaction time for 10mL of Na2S2O3.

Observations: (6 marks)

Trial 1 / Trial 2 / Average Reaction Time (sec.)
Volume of Na2S2O3 / Volume of H2O / Moles of Na2S2O3 (mol) / Reaction Time (sec.) / Volume of H2O / Moles of Na2S2O3 (mol) / Reaction Time (sec.)
50 drops
40 drops
20 drops

Manipulated data: (6 marks)

Drops of Na2S2O3 / Reaction rate (mol/s) / Reaction rate (mol/min) / Reaction rate (molecules/hr)
50
40
20

Sample calculations (show one sample calculation for each unit of rate): (6 marks)

1.  Rate (mol/s):

2.  Rate (mol/min):

3.  Rate (molecules/hr):

Analysis

Graph your data points (moles of Na2S2O3 vs. reaction rate in mol/min) to show the effect of concentration on rate of reaction. (5 marks)

Summary

Using collision theory, explain the effect of concentration on rate of reaction (2 marks):

______

______

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