From the experiment, the manipulated variable is the different contents with 5cm³ hydrogen peroxide while the responding variable is the effect on the glowing wooden splinter. The equation of the reaction that has been observed can be written as 2H?O? (aq) ————> 2H?O (l) + O? (g). In this experiment, enzyme catalase is responsible for the decomposition of hydrogen peroxide.
Catalase can be found in the peroxisomes of both plant and animal cell. In boiling tube 3, the liver that added into the boiling tube is pulped by using a glass rod. The reason to do so is to increase the surface area of liver so that there are more liver particles being exposed to hydrogen peroxide in order to speed up the decomposition of hydrogen peroxide. Therefore, the larger the surface area of liver, the higher the rate of decomposition of hydrogen peroxide.
While in boiling tube 2, the liver that added into the boiling tube is boiled in a water bath of 95ºC. When the liver is getting boiled, the enzyme catalase molecules in the liver move more violently as the water temperature increases. This causes the weaker bond in catalase such as hydrogen bond to break down followed by the breakdown of stronger bond such as ionic bond.
Next, the structures and surface configurations including the active site of catalase are altered. As a result, catalase loses its catalytic function and is completely denatured. Therefore, enzyme catalase will be denatured as the temperature increases, causing the hydrogen peroxide will not decompose. There are differences between the reactions of hydrogen peroxide and fresh liver or with fresh potato.
In boiling tube 1, the reaction between fresh liver and hydrogen peroxide shows a greater effervescence in which bubbles can be seen obviously and also in a large quantity. Besides, foams are formed above the mixture of hydrogen peroxide and liver. In boiling tube 4, the reaction between fresh potato and hydrogen peroxide shows effervescence too but the bubbles formed is in a lesser quantity and cannot be obviously seen. Meanwhile, when a glowing wooden splinter in inserted into both boiling tube 1 and 4, both glowing wooden splinter relights up with the glowing wooden splinter in boiling tube 1 burns with a bigger flame while the one in boiling tube 4 burns with a dimmer flame.
These differences are present because liver contains more enzyme catalase than potato. Liver contains more enzyme catalase because it is a site of many metabolic reactions and it detoxifies substances in the human body. A greater amount of catalase acts as an enzyme to overcome the activation energy in a biochemical reaction, causing the decomposition of hydrogen peroxide, a type of toxic waste from metabolic reactions to speed up.
But on the other hand, potato contains lesser enzyme catalase, thus it needs to overcome a higher activation energy in order to decompose hydrogen peroxide. As a result, decomposition of hydrogen peroxide slows down. When hydrogen peroxide reacts with boiled liver in boiling tube 2, the mixture does not show any effervescences and the glowing wooden splinter does not ignite when being inserted into the boiling tube. But when hydrogen peroxide reacts with heated manganese dioxide in boiling tube 6, the mixture reacts vigorously to form a lot of black foams and also the glowing wooden splinter ignites and burns with a bigger and vigorous flame when being inserted into the boiling tube. Besides, the reaction between hydrogen peroxide and heated manganese dioxide also releases heat as the boiling tube turns to be warmer.
Thus, it can be considered as an exothermic reaction. The reaction between hydrogen peroxide and boiled liver in boiling tube 1 does not have any observations because the enzyme catalase in the liver is denatured when being exposed to high temperature during boiling process. The enzyme catalase molecules in liver move violently as the temperature increases. As a result, weaker bond in catalase such as hydrogen bond will begin to break down followed by the breakdown of stronger bond such as ionic bond. This causes the structures and surface configurations including the active site of enzyme catalase to be altered.
Therefore, enzyme catalase loses its catalytic function and is completely denatured. On the other hand, the reaction between hydrogen peroxide and heated manganese dioxide shows obvious observations. This is because the particles of manganese hydroxide collide with each other more often during heating.
The particles will gain a lot of kinetic energy during the collision of one another. Therefore, manganese dioxide particles act as a catalyst and are able to overcome the activation energy during the decomposition of hydrogen peroxide. This is why the reaction between hydrogen peroxide and heated manganese dioxide has the greatest changes. Manganese dioxide is a type of catalyst but not a type enzyme so it will not decompose upon heating.