The difference between a chemical and physical change is that in a chemical change the substances undergo a change and become a new substance. Signs such as color change, bubbling and fizzing, light production, smoke, and presence of heat are signs of a chemical change.
In a chemical change, there’s a reactant and a product. For example, if we take sodium and chloride together (they are the reactants) we will end with sodium chloride (the product). Three common indications of a chemical change is evolution of heat and light, production of a gas, and formation of a precipitate.
Purpose
The purpose of this lab is to: observe chemical and physical changes, identify a chemical and physical change, and compare and contrast chemical and physical changes in matter.
Materials and Methods
The materials needed for this lab are the following: 3 test tubes (18 × 150 mm), 3 test tubes (13 × 100 mm), a laboratory burner, a ring stand and a ring, a clay triangle, a glass slide, a wood splint, a magnifying glass, a crucible, a test tube rack, a test tube holder, forceps, a graduated pipette, a spatula, and micro scale beakers.
The lab consists of six different experiments. For the first experiment; heating a wood splint, obtain the wood splint and break it into little pieces and place them in the test tube. With the test tube holder, place the test tube on the clamp. Heat the test tube strongly over the Bunsen burner for several minutes. After the experiment is done allow the test to cool off so it can be washed up. The second experiment; NaCl and water, place a spatula of sodium chloride in 2 to 3 mL of distilled water. Mix and place the two drops of the resulting solutions on a glass slide. Pass the slide back and forth over a low flame. Examine the residue after the liquid has evaporated. Then, compare the residue to a fresh sample of NaCl. The third experiment; Heating copper, obtain a clean, dry crucible. Make sure to dry the crucible to avoid having any other substances that will affect the experiment. Heat it strongly for 2 to 3 minutes and then allow the crucible to cool. Caution: Handle the hot crucible with tongs. While the crucible cools, obtain a small amount of copper turnings. Roll the copper into a ball about 2 cm. in diameter and place the ball in the crucible. Measure the mass of the crucible and copper to the nearest 0.01 g. Then, heat the metal in the crucible over a hot flame for five minutes, allow it to cool, and then remeasure. For the fourth experiment; heating Cu(NO3)2. Caution: Make sure not to inhale the fumes and avoid skin contact. With the use of the spatula, obtain a few crystals of copper(II) nitrate, and place them in a large test tube. Heat the test tube slowly over a low flame until a change is observed and then heat strongly to complete the reaction. Let the mixture cool, and add 10 drops of dilute nitric acid and heat gently. The fifth experiment, Combining solutions, obtain the twelve-celled micro-beaker and mix the following solutions. To 5 drops of barium nitrate, Ba(NO3)2, solution add 2 to 3 drops of sodium chromate, Na2CrO4, solution. Observe and record your results. To 5 drops of iron chloride, FeCl3, solution add 2 drops of potassium thiocyanate, KSCN, solution. Observe and record your observations. To 5 drops of iron chloride solution add 2 drops of silver nitrate, AgNO3, solution. Observe and record your observations. Below is a picture of the 12 well miscroscale.
1. Sodium chromate
5. KSCN
9. Iron (III) chloride
2. Ba(NO3)2
6. AgNO3
For the sixth experiment, obtain a small piece of calcium carbide with forceps and make sure to have gloves on since it reacts with water (and your body is made up of 70% water). Place it in an evaporating dish containing 25 mL of water add AJAX laundry detergent around the licorice, and with a small wood splint ignite the bubbles.
Data
Table 1 Physical Constance
Results
For the first experiment, within a couple of seconds, a smell of burnt wood, a smoke appeared in the test tube, and the wood at the bottom of the test tube turned black. This reaction is classified as a physical change because even though the piece of wood splint turned black, it is still identifiable. In the second experiment, the sodium chloride and water dried up and turned to a type of white, dry glue. In comparison to the original sample sodium chloride the mixture was powderized instead of crystals. This reaction was a physical change, also because it went from the liquid phase to the solid phase after heated. In the third experiment, the measurement of the mass before heating the copper was 29.29 g. and after heating the copper the mass was 29.45g. This was a physical change because the mass increased but the matter was still recognizable (an extensive physical property). In the fourth experiment, when the copper was heated it turned into an emerald green liquid before the drops were added. After the drops were added the copper turned brown. This reaction was a chemical change because it involved two or more substances that made another different substance. The fifth experiment involving the combination of solutions was a chemical change because two substances were mixed together which made a new substance. The first product was a milky and cloudy yellow, the second product seemed like grape juice or a dark, thick purple, and the third product was a cloudy, clear yellow. In the sixth experiment, the calcium carbide reacted with the water in the dish and it bubbled. There was gas inside the bubbles; therefore, when the bubble put the lit wood splint it made a small explosion sound. This experiment was a chemical change because there was a production of gas in the bubbles.
