PUTANGINA

Posted at 02:50 PM on October 21, 2009.

Curse. Curse. Curse. Curse.

I wish my dad is still alive. I wish he's here.

Curse. Curse. Curse. Curse.

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Organic Chemistry

Posted at 07:14 PM on August 23, 2009.

Paranoid

Abstract

This experiment was performed to determine the sublimation and melting point of benzoic acid. The sublimation set-up was used to purify the benzoic acid and collect its sublimate, which was required in determining its melting point and compare it with a standard. Only .1g of the sublimate was obtained, thus making its percentage recovery 2%. This just shows that the original 5g of impure benzoic acid will only yield a small amount of sublimate. As for its melting point, the sublimate had a 10°C range in temperature as compared to the benzoic acid with an 8°C range. Hence, it can be said that the sublimate is impure because there is a wide melting point range.  

Sublimation is a technique used by chemists to purify solid mixtures as long as the impurities are non-volatile or have a lower vapor pressure compared to a pure compound. Melting point on the other hand is the change in state of the compound from solid to liquid. In this experiment, impure benzoic acid undergoes sublimation to be purified, and the sublimate obtained is used for the melting point determination.

The objectives of this experiment are: to be able to purify the benzoic acid by sublimation, to determine the melting point of the product so as to compare it with a standard, and to calculate the percentage recovery of the sublimate.

Experimental

5 grams of impure benzoic acid was placed in an evaporating dish covered with a perforated bond paper and a pre-weighed watch glass. A moist tissue was also placed on top of the set-up to cool the center. The contents were then heated for 10-15 minutes using a hot plate and were left to cool after heating. The group then collected the sublimate and placed it on the pre-weighted watch glass and was weighed again for determining the percentage recovery.

For melting point determination, the sublimate was grinded into fine powder and was placed in a capillary tube. The latter and the standard were then attached to a thermometer using a rubber band and were immersed in an oil bath for heating. The group recorded the temperature in which the sublimate and the benzoic acid started to melt and when it has completely melted. Lastly, after both data were obtained, both melting points were compared.

Results and Discussion

After performing sublimation, only .1g of the solid benzoic acid volatilized and was condensed as a purified compound (sublimate) while the non-volatile residue impurities were left behind. Because of this, the group was able to obtain a percentage recovery of only 2%.

As for the melting point of benzoic acid, the temperature at which it started to melt was 126°C and it completely melted at a temperature of 134°C. On the other hand, the temperature at which the sublimate started to melt was 122°C and it completely melted at 132°C. The range of the melting point of benzoic acid is 8°C as compared to the sublimate’s 10°C. Hence, the sublimate is considered impure because it has a bigger range as compared to the benzoic acid.

The range is a basis for determining if a substance is either pure or impure because if the range is broad, more impurity is present in the substance. In contrast to if the range is small, it can be said that the substance is pure. Furthermore, the melting point of a pure substance is always higher than the melting point of an impure substance.

References

Xavier University of Louisiana, Department of Chemistry. (2006). Determination of Melting Points. Retrieved August 14, 2009 from the Xavier University of Louisiana website:

http://www.xula.edu/chemistry/department/organic/Notes/06MP.pdf

Melting point. (2009, August 7). In Wikipedia, the free encyclopedia. Retrieved August 14, 2009, from http://en.wikipedia.org/wiki/Melting_point

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Paranoid

Posted at 07:11 PM on August 23, 2009.

Introduction

Chromatography is defined as any of various techniques for the qualitative or quantitative separation of the components of mixtures of compounds; all characterised by the use of a mobile phase (gas or liquid) moving relative to a stationary phase (liquid or solid). It is also a separation technique used for identifying compounds.  Two types of chromatography were used in this experiment; column chromatography and thin layer chromatography.  Such chromatographic methods were used because the experiment dealt with two phases, solid and liquid.  The objectives of the experiment are:  to be able to separate the colored pigments of siling labuyo and malunggay leaves using column chromatography, to determine the purity of the components using the thin layer chromatography, and to measure the Rf values of the colored components.

Experimental

Column Chromatography

Red siling labuyo and malunggay leaves were grinded separetly to extract the colored pigments. Upon grinding, it was eluted by adding DCM-hexane (1:1) to siling labuyo and hexane:acetone (7:3) to malunggay leaves. While waiting for the extractions, the other members of the group already prepared the set-up for column chromatography. To create the set-up, they get a Pasteur pipette, plugged small piece cotton at the narrow end of it, filled it with silica gel up to the indented part of the Pasteur pipette, and suspend it in an iron stand.  They made two set-ups, one for each extract. After getting the extractions,  0.5 ml of each crude extract was dropped on top of the column and 3 ml of each eluents was added to separate the colored components; hexane: acetone (7:3), DCM-he

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Seesh

Posted at 09:40 PM on August 20, 2009.

It wouldn't kill you if you try to hush for a sec. Geez.

Keep Mum.

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