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Pre-Lab Questions Daniel Wang What are the key indicators of a chemical reaction? A chemical change happens when there is a reaction in a substance that changes its composition, essentially making it a new substance. Some key indicators of a chemical change include: bubbling, absorption of energy, change in color, and change in odor. What physical reactions can be misunderstood as chemical reactions? A physical change that can be misunderstood as a chemical change include the change of state. For example, some believe that when water changes from a liquid to a solid it is an example of a chemical reaction. However, this is not true because the chemical make up did not change, the substance is still H2O. What are two ways that physical properties can be presented? Provide examples. Two ways that physical properties can be presented are in quantitative and qualitative form. For instance, a quantitative form is presented numerically: the bottle has a length of 60cm. Qualitative forms, such as the boiling point of a substance are not measured numerically. What does the Iodine and Universal indicator test for? The universal indicator tests for the acidity or alkalinity of solutions. On the other hand, iodine tests for starch present within a substance. What substances in this lab could be harmful to you? The environment? In this lab, various powders can be harmful to me if I am not wearing the proper personal protective equipment. For example, without goggles, the powder can infect my eyes. In addition, some powders can be dangerous for the environment. If the powder is spilled on a surface and not cleaned, it could do harm to someone who is not aware of its presence (we must follow the proper clean up procedures) What is the purpose/benefits of scientific method? The purpose and benefit of the scientific method is that it makes sure that the insight gathered from the experiments are as valid as possible. How can physical and chemical properties help a scientist identify a substance? Physical and chemical properties can help a scientist identify a substance because the make up of every substance is different. Scientists will be able to identify with a sample of 1g or 100 tons. Post-Lab Questions *change in color happened when the Iodine solution was added Identify any evidence of chemical changes in each test. 1. 2. 3. 4. 5. 6. 7. Icing sugar - change in color (white powder + Iodine solution = black substance) Cornstarch - change in optical clarity Flour - change in color (green) Baking soda - bubbling Baking powder - bubbling Crushed antacid - bubbling Mystery powder - change in color (black) What do the testing substances tell you by their reaction or lack of reaction? The reaction or lack of reaction in a substance can tell us about its reactivity. Reactivity is the tendency of a substance to undergo chemical reaction, either by itself or with other materials. For example, I found the baking soda very reactive as it underwent a chemical change with three of the four substances. On the other hand, the icing sugar was not very reactive as it only underwent chemical change with one of the four substances. Use evidence provided by the tests to identify mystery powder. According to my tests, the mystery powder is baking powder. To begin, it poses the same physical properties as baking powder. For instance,the are both small and white. In addition, the mystery powder and baking powder reacted the same with every substance. For example, they both turned green when the universal indicator was added. Which properties, physical or chemical, were most useful in identifying the powder? Explain your answer. The chemical properties were clearly more useful in identifying the mystery powder. To begin, all of the powders were extremely similar, white, odorless etc. However, when the powder reacted, the results were different for many of the substances. By finding which results match all of the tests from the mystery powder, it was easy to identify the substance. What physical properties could have helped to identify the mystery powder? Why were these properties not tested in this activity? A couple of physical properties that could have helped identify the mystery powder include taste and the density. Firstly, we could not have tasted the mystery powder as it is unknown and therefore could be harmful when consumed. However, by tasting the powder, we could identify it through its bitter taste. Following, the crystals are extremely small and we do not possess the proper equipment to test its density, mass, or volume. This test could have helped as we know that the density of baking powder is 2.173g/cm3. You find a puddle of clear colorless liquid in your driveway. It is water, vinegar or spilled battery acid from the car. How can you safely test the liquid to determine its identity? Explain how you can interpret your observations. There are a couple simple way in which we can identify if the substance is either vinegar or battery acid. To begin, each liquid has its own unique smell. This can be tested by safely whiffing the substance. Next, the battery acid is acidic, therefore if we put a small piece of fabric in the liquid, it should erode if it is battery acid. If not, then we know that it is vinegar.