How does concentration affect rate? (Practical). Flashcards
What is the disapearing cross reaction?
- Sulfur makes the solution cloudy.
1) using a measuring cylinder pour 10cm^3 of sodium thiosulflate solution into a conical flask.
2) Place conical flask on top of a black cross.
3) Add 10cm^3 of hydrochloric acid into the flask.
4) Swirl the solution and start the timer. Look down from the top of the flask. After a certain time the solution will turn cloudy.
5) Stop the clock when we can no longer see the cross.
6) Repeat using lower concentrations of sodium thiosulflate.
7) Repeat the whole experiment. Calculate mean values for each concentration.
What is a reproducible measurement?
- A measurement is reproducible if it can be repeated by another person or using a different technique or equipment and get the same results.
What is the problem with the dissapearing cross experiment?
- Different people have different eye sights.
- Some people can see the cross longer than others so may not get the same results.
HOWEVER: - As the cross is the same size this problem may not be too great.
What is the second practicle we can use for concentration?
1) Use a measuring cylinder to place 50cm^3 of hydrochloric acid into the conical flask.
2) Attach the conical flask to a bung and delivery tube and place the delivery tube into a container filled with water.
3) Place an upturned measuring cylinder also filled with water over the delivery tube.
4) Add 3cm of magensium to the hydrochloric acid and start to stopwatc.
5) Reaction produces hydrogen gas. Every ten seconds measure the volume of hydrogen gas in the cylinder until no more is given off.
6) Repeat using different concentrations of hydrochloric acid.
What do these reactions show?
- Greater concentration of a chemical in the reaction the faster the reaction takes place.
- Because the results are shown using to different experiments and are the same this is reproducible.
