Characteristics of Matter (chem 14.1)

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The third and final part of the experiment saw the changes of the components of the mixtures.

A pinch of Fe, food coloring, table salt, and two iodine crystals were placed separately in 20 mL test tubes, heated gently with a low flame and observed for any visible results. The test tubes were cooled and the walls of the upper portion of the test tubes were examined to identify the types of changes that had taken place and the experimental evidences for these types of changes. Procedures 2 and 3 for part B were recalled to identify the changes that took place and the experimental evidences for these types of changes.

A small piece of iron and magnesium were placed in two separate test tubes, added with 10 drops of 0.1 M hydrochloric acid. Observations were recorded, and the type of chemical change that took place was identified. All of the filtrate that was saved from experiment A was placed in an evaporating dish, added with a piece of red litmus paper and evaporated to dryness.

V. Results and Discussions

5.A1 Physical Properties

Physical properties of the substances were observed. The color of the iron filings were black and had dusty fragile texture, the mothballs were white, smooth and powdered, white and rough crystalline for table salt, grayish black and smooth for Mg ribbon and, orange and powdered for the food coloring.

5.A2 Physical Separation

Table 1: Results of experiment 1, part A, physical separation of substances by performing different separation techniques

1. Iron (Fe) filings

4. Mothballs

2. Charcoal / Food coloring

5. NaCl (Table Salt)

3. Mg Ribbon

6. Iodine( I2)

In the first part of the experiment, iron (Fe) fillings, ground mothballs, salt, magnesium (Mg) ribbons and food coloring were scattered on a piece of paper. With the use of a magnet, the Fe fillings were separated from the rest of the mixture. Although magnesium is also a metal element, iron was the only one attracted to the magnet since it has unpaired electrons which are attracted by a magnetic field due to the electrons' magnetic dipole moments.

The components that were not separated were placed in a beaker with 30mL water. The mixture was then filtered after stirring. This method called filtration separated the solid particles that were not able to permeate the filter paper. While the filtrate was saved, the residue was heated in an evaporating dish using a certain setup.

The residue for this part was the Mg ribbon which remained in the dish and the ground mothballs which were deposited on the walls of the inverted funnel that trapped the gas that would evaporate. The separation technique used was sublimation. Sublimation is used to separate solids which have high vapor pressure since they directly change into vapor upon heating, changes to solid upon cooling. (Amrita University, 2011). The mothballs is one of these solids, therefore it sublimes readily at 1 atm.

Once the residues were identified, the filtrate was then boiled and a pinch of activated charcoal was added. After boiling, the mixture was again filtered. The filtrate became clear and the orange color from the food coloring was gone; the charcoal was the residue. Adsorption, the process in which atoms, ions or molecules from a substance adhere to a surface of the adsorbent, occurred in this reaction. (“Absorption,” 2016). In this case, the food coloring served as the adsorbate that clung to the charcoal which is porous and acted as the adsorbent.

Iodine crystals (I2) and 1mL of hexane were then mixed with the filtrate. The mixture resulted to two layers: a purple hexane layer, and an aqueous layer. The two layers were separated through the solvent-extraction technique. This is a method for separating a substance from one or more others by using an organic solvent such as hexane (McMahon, 2003). The change in color of the hexane layer denoted presence of iodine. This layer is the immiscible non-polar layer, thus the aqueous layer is polar. The iodine from the water solution was extracted by hexane.

Both of the layers were evaporated in a hood. The solvents (water and hexane) evaporated. Salt was left in the evaporating dish that contained the aqueous layer while the iodine in the other dish also turned to gas when it was heated. This method is called distillation, where components of mixtures are separated according to their different volatilities.

5.B1 Analysis of Components: 0.1 M HCl

In part B, the components of the mixture were classified. The Fe fillings, Mg ribbons, I2 crystals and ground mothballs were put in separate test tubes. Ten drops of 0.1 M hydrochloric acid (HCl) were then added to each and covered with cork stoppers. While the others did not result to any reaction, evolution of gas occurred in the test tubes with Fe and Mg. The reactions of each element are shown below:

2Fe(s)+ 6HCl(aq)→2FeCl3(aq)+ 3H2(g)

Mg(s)+ 2HCl(aq) →MgCl2(aq)+ H2(g)

This showed that half of the pure substances (Fe and Mg) were metallic and had continuous evolution of gas when reacted with 0.1 M HCl. On the other hand, Naphthalene balls and iodine were non-metallic because there was no continuous evolution of gas.

5.B2 Analysis of Components: Oxygen

In most cases, metals react with an acid to form a salt and release hydrogen gas. Therefore, the gas that was produced in the test tube was hydrogen gas. This is confirmed through testing the gas with a splint. Hydrogen gas is flammable, producing a popping sound as it is burned in the test tube. Subsequently, Mg and S were burned to test the reaction of oxides with water:

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The oxides were placed in a test tube and then added with water:

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Magnesium Oxide (MgO) readily becomes Mg(OH)2 which is a base. A great amount of energy is needed to break the ionic bond of MgO. This reaction is exothermic since the energy released is in the form of heat. On the other hand, the second one