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Total Surface Area and Rate of Reaction

By ReneAllard May 19, 2013 1020 Words
Antacid tablets are used to relieve heartburn and neutralise stomach acid. Planning
Aim
To determine how the surface area of the tablets affects the rate of the reaction. To determine which form of tablets gives the biggest surface area resulting in the fastest reaction rate.

Investigation question:
What is the relationship between the total surface area of the tablets and the rate of the reaction?

Hypothesis:
The rate of reaction will be the fastest when the tablets crushed into powder as there is a bigger total surface area resulting in more effective collisions between particles.

Variables:
Independent variable: Different forms of tablets.
Dependant variable: Time the syringe took to stop moving as the tablets dissolve. Fixed variables:
*External temperature
*volume of HCl
*Temperature –all 3 final runs were done on the same day so whether was not an issue and did not affect the results *Use of catalyst – a catalyst was not used in any of the experiments * Use the same person to observe the reaction because different people have different eyesight Background information relating to the experiment

In this experiment we are looking at one effect that influences the rate of reaction , namely total surface area. The reaction rate (rate of reaction) or speed of reaction for a reactant or product in a particular reaction is defined as how fast or slow a reaction takes place. As the surface area of the reactants increases, the reaction rate increases. This is because increasing the surface area of the reactants results in a higher number of reaction sites. Increasing the number of reaction sites increases the number of total collisions. The greater the frequency of total collisions, the greater the frequency of effective collisions. If the frequency of effective collisions increases, so does the reaction rate. Surface area is one of the factors that increases the rate of reaction. Other factors include: 1. Concentration. As the concentration of the reactants increases, the reaction rate increases. According to the collision theory, the rate of a reaction is directly proportional to the number of effective collisions per second between the reactant molecules. If the concentration of the reactants increases (i.e. particles per given volume) the greater the number of total collisions. The greater the frequency of total collisions, the greater the frequency of effective collisions. If the frequency of effective collisions increases, so does the reaction rate.

2. Temperature .As the temperature of a system increases, the reaction rate increases. Temperature (T) - A measure of the average kinetic energy (KEavg) of the particles of a substance. Increasing T increases KEavg. At higher T, the fraction of molecules with energies greater than the activation energy (Ea) increases.

3. Catalysts. The presence of a catalyst increases the reaction rate. It does so by lowering the activation energy of a reaction. Possible ways of lowering the Ea of a reaction: a. Increases the frequency of collisions between the reactant molecules. b. Changes the relative orientation of the reactant molecules. c. Donates electron density to the reactant molecules. d. Reduces the intramolecular bonding within the reactant molecules. e. Provides an alternate pathway or mechanism for the reaction. Surface area in everyday life and in the body:

IN BIOLOGY: The surface area of an organism is important in several considerations, such as regulation of body temperature and digestion. Animals use their teeth to grind food down into smaller particles, increasing the surface area available for digestion. The epithelial tissue lining the digestive tract contains microvilli, greatly increasing the area available for absorption. Elephants have large ears, allowing them to regulate their own body temperature. In other instances, animals will need to minimize surface area; for example, people will fold their arms over their chest when cold to minimize heat loss. Different experiments dealing with rate of reaction:

The experiments I could do are:
• Measuring volume of gas produced
• Measuring precipitation (because sulphur is produced) e.g. look for ‘X’ to disappear • Measure mass lost
1. How concentration of sodium thiosulphate affects rate In this experiment we did a trial run to familiarise ourselves with the experiment and the equipment. It also helps us what kind of patterns we expect to get. The concentration of sodium thiosulphate was changed by adding water. The solution was tested to see if it goes cloudy by observing an ‘XMethod: In trial run 1 we used a solution called sodium thiosulphate to measure how long it takes to turn cloudy when you mix a certain amount of water and acid to it. The way we measured how the solution has turned cloudy is by: • Draw an ‘X’ on a piece of paper and place under a conical flask. • Measure volumes of sodium thiosulphate and water using results table • Add 3ml of HCL into the flask.

• Immediately time how long it took until the ‘X’ was no longer visible, how long it took for the solution to turn cloudy The person observing when the ‘X’ disappeared then recorded the time.’.

Design
Apparatus
* Beaker
* Hydrochloric acid (HCl)
* A measuring cylinder
* A funnel
* A syringe
* A stopper connected to a tube
* A stopwatch
* A bowl
* A crusher
* One box of antacid tablets
* A notebook

Setup of the apparatus

Method
1. Make sure all apparatus are clean
2. Connect the rubber stopper and tube to the syringe.
3. Make sure more air can escapes.
4. Use a funnel to pour 30 ml of Hydrochloric acid into measuring cylinder. 5. Pour HCl into a beaker.
6. Make sure the stopwatch is reset.
7. Place 2 whole antacid tablets into the HCl solution.
8. Close the beaker immediately with the rubber stopper.
9. Record the movement of the syringe every 15 seconds.
10. One the syringe stops record the experiment 3 times with 2 whole tablets. 11. Record results and take averages.
12. Thereafter do the experiment again but with 2 tablets broken into quarters and repeat 3 times. 13. Do experiment with 2 crushed tablets (powder) and repeat 3 times. Crush the tablets in the bowl using a crusher.

Make sure the apparatus is cleaned before each new trial and that the syringe is dried out.

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