DAY 1 -17th May
Our experiment is designed to investigate the effect different enviroments have on the rate a bath bomb dissolves. These factors include changing the temperature of the water, changing the surface area of the bath bomb and changing the pH of the water. Therefore we are looking for the ideal bath conditions which ensures the bath bomb lasts longest.
1.Having already bought 3 bathbombs from 'Lush', we first decided to test the effect temperature has on the rate of reaction.
Apparatus1 large glass container
Kettle
Thermometer
Ice
Stopwatch
Scales
3 bath bombs
Measuring cylinder
Pestle and mortar
Knife and tile
Method
We took one bath bomb and divided it into four equal parts, each measuring an average of 16.5 g.
We set up a water bath in the large glass container at temperatures of 20ºc, 40 ºc, 60 ºc, 80 ºc and 90 ºc. We ensured the volume of water was kept constant, at 2100 ml.
Once the temperature was reached, we added the bath bomb to the water and started the stop watch, measuring the amount of time the bath bomb took to stop reacting with the water and we could no longer see effervescence, i.e. it had dissolved.
Conclusion
From our results we could see that as temperature increases the time taken for the bath bomb to dissolve decreases. Heat increases the rate of reaction because it provides the particles with more kinetic energy. This means that they move faster, thus increasing the chance of collision with the water particles, and so it is able to dissolve at a quicker rate.
2. We then decided to see the rate of rection depending on the surface area.
Method
We cut the bathbomb into 4 parts weighing equal amounts. With one quarter we left it whole, the second we divided it, the third we cut it into lots of chips + with the final part, using a pestle and mortar, we made it into powder. We made sure the volume of the water and the temperature was kept the same each time.
Conclusion
Our results show that the powdered bath bomb dissolved the quickest in only 20 seconds, wheres the bathbomb in one piece took 127 seconds to dissolve. Therefore, the greater the surface area of the bath bomb, the faster it will dissolve, as more particles are exposed to water particles and so more collisions occur, thus increasing the rate of reaction.
Evaluation
- calcium residue at the bottom of the kettle could have affected the pH of the water
- we weren't able to cut the bath bombs equally because they crumbled easily, and so their masses weren't exactly the same ; this could have affected the rate as a larger mass would take a longer time to dissolve
- when we added ice to control the temperature the volume of water would have been increased without us recording it
- when we time it is hard to start the stopwatch as soon as the bathbomb hits the surface and stop it the moment the dissolving is complete
