Identifying Unknown Substances

After each of the solids were completely dry, each was placed into a MelTemp device. The temperature at which each solid began to melt and completed melting was recorded.

The melting point of a compound is used by organic chemists not only to identify the compound, but also to establish its purity. To determine the melting point two temperatures were noted. The first was the point at which the first drop of liquid formed among the crystals; the second was the point at which the whole mass of crystals turned to a clear liquid. And the melting point was recorded from this

8. Crush crystals into powder with a stirring rod and use a melting point device to determine the melting point of your active ingredient.

In the first part of the experiment trans-cinnamic acid began to melt rapidly at 133 °C and had completely liquefied at 135.9 °C. Urea began to melt rapidly at 133 °C, just as the trans-cinnamic acid, but had completely liquefied at 134.7 °C. Both urea and trans-cinnamic acid had true melting points of 132 °C generating a .75 percent error. The 50:50 mixture of urea and trans-cinnamic acid started to melt quickly at 98.5 °C, slowed down at 102 °C, at which point most of the compound had seemed to have melted with the exception of a few crystals, which did not melt completely until 125°C . In the second part of the experiment, the melting point of an unknown compound was measured at a fast rate, 10 °C/min, in order to obtain an estimate of the melting point of that compound, which was about 130 °C – 139 °C. At this point the suspected organic compound was benzoin, and the melting points of the two compounds, benzoin and the unknown, as well as the 50:50 mixture of each, were obtained. The unknown compound, along with the benzoin, had identical melting points of 133.7°C – 134.9°C, while the 50:50 mixture had a melting point of 133 °C – 134.3 °C. The true melting point for benzoin is 132°C, generating a .75 percent error.

Toulene, I was not familiar with but was surprised that it was not soluble in water. What I did enjoy doing was trying to determine the unknown substances by applying physical properties to them. To be able to find the density, find a melting point or a boiling point, and use the refractive index to first record the observed results and then be able to compare them to Table 1, the Physical Properties of Pure Substances Chart and actually be able to determine what the unknown substance is based on a comparison of the observed data compared to the chart. One problem we encountered was trying to decide the melting point of our unknown solid, we waited to long to record the initial melting state I believe. I also believe that we did not let the liquid unknown reach it’s full potential on boiling point.

Experiment 3: Identification of an Unknown Mixture by Extraction, Recrystallization and Melting Point Determination Alex Presello 103402448 Lab Completed: October 10th, 2014 University of Windsor  Experiment 3: Identification of an Unknown Mixture Abstract The purpose of this experiment was to first, extract two of three possible organic compounds from an unknown organic mixture (#2) and second, to identify them. The two main methods of separation used in this experiment were liquid-liquid extraction and recrystallization. In order to determine the identity of the unknown compounds, their respective experimental melting points were found and compared to the known melting points of compounds based on previous literature.

Have you ever wondered that if you put ice into a drink, the substances in the drink will make it melt faster. This is exactly the case, I will be seeing how the substances that we use in our everyday life affect the melting point of ice. I will be looking at what causes the freezing point depression, how substances affect the freezing point of ice, and the purposes of changing the freezing point of ice. The melting point of ice is the given temperature that a substance will melt, and by lowering this it makes the ice melt quicker. By learning this you can understand which substance to use to melt the ice off of your sidewalk, or even when making homemade ice cream.

The theory for the melting point is that it helps with the indication of how pure a substance is, also it helps in figuring out the melting point of the purer substances, sharper melting points belong to more pure substances (Online Labs). Also melting points can be affected by the size of the molecule and intermolecular forces (Online Labs). Melting point was measured using the melting point apparatus. That being said it is very important to ensure that there is minimal impurities or the apparatus is not overly heated, this will lead to inaccurate data as it will give the wrong readings (Landrie, 193). The best way to ensure that the most accurate measurement is gotten to cool the apparatus to 10 -15 degree Celsius then taking the measured when it is heated to 1-2 degrees Celsius (Landrie,

A compound can be identified by its physical properties like melting point, boiling point, and density. The melting point can show how pure a compound is. The purer the compound, the higher the melting point and the narrower it’s melting point range. Adding continuous amounts of impurity to a pure compound will cause the melting point to decrease. In this experiment the melting point of crystalline substances are observed to see how pure the compound is. This was done by putting the compounds into a capillary tube. The capillary tube is then inserted into a melting point apparatus and heated. The temperature at which the compound begins to liquefy and when the compound becomes completely liquefied will show how pure the substance is. The melting

A physical property is a quality of a substance that can be observed or measured without changing the substance’s composition. An example of a physical property is color and hardness. A chemical property is when a substance undergoes a chemical change or reaction which change the identity of the substance. An example of a chemical property would be heat of combustion.

The objectives of this lab are, as follows; to understand what occurs at the molecular level when a substance melts; to understand the primary purpose of melting point data; to demonstrate the technique for obtaining the melting point of an organic substance; and to explain the effect of impurities on the melting point of a substance. Through the experimentation of three substances, tetracosane, 1-tetradecanol and a mixture of the two, observations can be made in reference to melting point concerning polarity, molecular weight and purity of the substance. When comparing the two substances, it is evident that heavy molecule weight of tetracosane allowed

The melting point of a product is an index of its purity. The closer the observed melting point is to the literature value, the more pure the product. Additionally, the range of the observed product

Our senses are limited in that they strictly give us information about things but they do not interpret that information for us. We have to appeal to the mind every time we experience sensible objects. We constantly go to the mind to determine what the inherent quality of the thing is that makes it that thing. It is something that we cannot sense. There are two types of substances in our world; extended substances and thinking substances. Thinking substances are things in the mind and they do not physically exist. Extended substances are known to be what is called as material substances, meaning they are physical in their existence.

Physical changes can be seen through an altering of the substances physical property. A substances physical property is observed and measured without changing the composition of the subject. Descriptive words that would help to identify a substance’s physical property include hard, soft, brittle, flexible, heavy, and light just to name a few.

Brittain, C. G. (2009). Using Melting Point to Determine Purity of Crystalline Solids. Retrieved from http://www.chm.uri.edu/mmcgregor/chm228/use_of_melting_point_apparatus.pdf