1 / 13

HOW FAST?

HOW FAST?. Effect of concentration on rate of reaction. You will investigate the effect of concentration or temperature by mixing a solution of sodium thiosulphate with hydrochloric acid : Na 2 S 2 O 3 (aq) + 2HCl (aq)  SO 2 (g) + S (s) + H 2 O (l) + 2NaCl (aq)

weylin
Download Presentation

HOW FAST?

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. HOW FAST? Effect of concentration on rate of reaction

  2. You will investigate the effect of concentration or temperature by mixing a solution of sodium thiosulphate with hydrochloric acid : Na2S2O3(aq) + 2HCl(aq) SO2(g) + S(s) + H2O(l) + 2NaCl(aq) The sulphur formed will make the solution go cloudy and you can use the time it takes for this cloudiness to appear to find the speed.

  3. Choosing a range The highest concentration of thio available contains 0.2 moles per litre of solution (0.2M) It would be a good idea to have 5 or 6 readings So a suitable range would be from 0.04 to 0.2M With an interval of 0.04M

  4. Identifying Variables To investigate the effect of concentration on reaction rate Concentration is the independent variable (we can choose which concentrations to use) Reaction rate is the dependent variable. (Rate depends on concentration) We cannot measure reaction rate directly: instead we can measure the time taken.

  5. To make our experiment valid we must • Keep the temperature constant (since the reaction would get faster if the temperature rises) • Keep the volume constant (so that we are always looking at the black cross through the same depth of solution • Use the same black cross (because another cross might be darker or fainter)

  6. COLLISION THEORY • REACTIONS OCCUR WHEN PARTICLES (e.g. molecules) COLLIDE • ANYTHING WHICH INCREASES RATE OF COLLISIONS, INCREASES RATE OF REACTION • INCREASING THE CONCENTRATION MEANS THERE ARE MORE PARTICLES IN THE SAME VOLUME • SO COLLISIONS WILL HAPPEN MORE FREQUENTLY

  7. Now we need to calculate rate or speed of reaction The faster something happens, the shorter the time taken. Calculate 1/time as a measure of rate (or speed)

  8. Now plot the results as a graph: Draw in a line of best fit

  9. Collision Theory and effect of concentration • The graph shows that reaction rate is directly proportional to concentration • This is a causal relationship: if there are more particles in the same volume then there will be more collisions every second

  10. Random Errors • The measuring cylinders were sensitive to the nearest 0.5 or 1 cm3. • So readings of volume are only reliable to plus or minus 0.5 cm3 • The system for timing (stopwatch + reaction time) was only sensitive to about 1 or 2 seconds.

  11. If I repeated the readings, I could • Identify any anomalous readings • Improve the reliability of my results • If I used better measuring equipment my results would be more precise • If I took a lot more care I might obtain results which are more accurate.

  12. There were some systematic errors in my experiment • It is impossible to add all the acid instantaneously • so I started the stopwatch when half of it had been added • I couldn’t judge exactly when the black cross had disappeared • I could only mix the chemicals after I had started the stopwatch and some reactions may have been mixed better than others • The temperature may have gone up during the lesson, making the reactions get faster • But these errors are small so my results are still valid.

More Related