Agar Lab

Topics: PH, Molecular diffusion, Measurement Pages: 10 (3272 words) Published: November 29, 2008
What effect does the different concentration of hydrochloric acid have to the rate of diffusion of agar that is dissolved with sodium carbonate and phenolphthalein?

Diffusion is a process where the molecules intermingle as a result of their kinetic energy of random motion and is the net movement of like molecules down their concentration gradient, which is the energy inherent in their constant molecular motion makes them collide and careen outward from the region of higher to lower concentration.

In our daily lives, many tasks are accomplished with the help of diffusion. For example, farting is considered to be diffusion, releasing a very high concentrated intestinal gas through the anus and out to the environment where there is a low concentration. By releasing that harmful gas, it can keep your body healthy. Agar is a phycocolloid and is extracted from several species of red-purple marine algae’s cell walls that are usually harvested in eastern Asia and California. Laboratory agar looks gelatinous because it is dissolved in boiling water and cooled. Agar can be easily distinguished from the other materials commonly found in a laboratory due to its distinctive smell. At room temperature, agar is a gel and it stays firm at 65ºC and melts at 85ºC. It solidifies when the temperature reaches 32 – 40ºC. It is used as various microoragnisms’ culture medium, especially for bacteria and it is also served as a thickening for soups and sauces, in jellies and ice cream, in cosmetics, for clarifying beverages, and for sizing fabrics. Agar is also used in medicines to promote peristalsis and relieve constipation and is resistant to a breakdown by bacterial enzymes. Sodium carbonate, Na2CO3, also known as washing soda or soda ash, is a sodium salt of carbonic acid. It can be extracted from the ashes of many plants and has a cooling alkaline taste. It is one of the most basic industrial chemicals. The acid’s Ph scale is always lower than 7. Phenolphthalein, C20H14O4, also written as “Hln” or “phph” in shorthand notation, turns into white or yellow colour in acidic solutions, for instance hydrochloric acid, and pink in basic solutions. It can also turn purple when the concentration of indicator is particularly strong. Usually, phenolphthalein is used to perform Kastle-Meyer test (a presumptive blood test) and used as an acid or base indicator by changing colours when contact with acid and base. It is also a solution in universal indicator, consisting of a mixture of pH indicators. The base’s Ph scale is always greater than 7. Hydrochloric acid is a gaseous inorganic compound and a strong acid. The acid’s Ph scale is always lower than 7. It must be handled with appropriate safety precautions because it is a highly corrosive liquid. Therefore, during the lab, the class had to wear goggles and aprons. If the concentration of hydrochloric acid is high, then the rate of diffusion will increase. The high the concentration of hydrochloric acid which results of a more dense acid and therefore the gravitational pull would act strong on the acid and causes the acid and the agar to diffusion faster.

In this lab, different concentrations of hydrochloric acid samples will be added to the agars with sodium carbonate and phenolphthalein. Each sample will have two millilitres of different concentrations of hydrochloric acid added to the agars with sodium carbonate and phenolphthalein for 20 minutes and this process will be repeated five times. When the hydrochloric acid and the agar with sodium carbonate and phenolphthalein react, the phenolphthalein neutralizes the hydrochloric acid, which equals 7 in the Ph scale, and the product will be a foggy layer in between the pink agar and the hydrochloric acid. By measuring the length of the white or yellow layer indicates the rate of diffusion. The rate of diffusion formula will be

The length of the white or yellow layer = Rate of diffusion...
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