Lab 4: Physical and Chemical Properties and Reactions

Transcription

1 Lab Materials: Tide TM powder detergent Cream of Tartar Lemon Juice Baking Powder Baking Soda Cornstarch Q-tips Rubbing alcohol Wax paper Sharpies (to label wax paper) Plastic spoons Medicine droppers Small or large plastic cups Water Lab 4: Physical and Chemical Properties and Reactions

2 Physical and Chemical Properties and Reactions Name: Date: Introduction Physical properties are characteristics a sample displays without changing its composition. For instance, how something looks, tastes, smells, and even its density are all examples of physical properties. A chemical property is a characteristic a substance displays only when it changes its composition. For instance, the gasoline you burn in your car is an example of a chemical property, in this case the gasoline s flammability. When matter changes form as it frequently does, two changes could take place. If a physical change takes place, the matter does not change its composition. Phase changes are examples of physical changes. If you think about leaving an ice cube on the kitchen counter, after a while the ice will begin to melt to leave a nice puddle. Even though the ice cube and the puddle of water look very different, they are still composed of water molecules. If a chemical change (or chemical reaction) were to take place, then the matter does change its composition. For this, think of a campfire. Before you started the fire, you had pieces of wood, but after the fire went out, all you are left with are ashes. In this case, we have a chemical change. In today s lab, you will complete exercises that help you gain a better understanding of physical and chemical properties and changes. Directions: 1. For part A, identify each as a chemical (C) or physical (P) property. For part B, classify each as either a physical (P) or chemical (C) change. Part A: 1. The smell of spearmint gum 2. Iron s ability to react with oxygen to form rust 3. Mercury being a liquid at room temperature 4. Baking flour s texture 5. An emerald s green color 6. Chlorine gas liquefies at 35 o C under normal pressure 7. Hydrogen burns in chlorine gas Part B: 1. Fingernail polish remover evaporating from a cotton swab 2. Salt dissolving in a cup of water 3. A car rusting 4. A mirror shattering 5. A granite statue being eaten by acid rain over several years 6. A strong acid reacting with a strong base to form water and a salt 7. Burning of sulfur

3 2. Complete the following table. Sample Laundry detergent Cream of tartar Air Lemon juice Baking powder Baking soda Cornstarch Physical State (s, l, g) Appearance (color, odor, texture ) 3. Soak a Q-tip in rubbing alcohol (wet, but not dripping). Drag it across a countertop to make a foot long streak. 1 You might have to wait several minutes to answer the following questions it depends on how wet your Q-tip was. a. What happens to the streak? b. Does this occur instantly, continuously or in stages? c. How long does it take? d. Are you observing a chemical or physical change?

4 4. When completing the table in problem #2, you probably realized that some forms of matter would be difficult to distinguish if they had not been properly labeled, i.e. your description of the substances appearance was very similar. In the next part of this lab, you will learn how you can distinguish between some of these substances through chemical reactions. To do this, you will need to mix three liquids with 5 powders. Use a piece of wax paper and medicine dropper(s) to conduct your experiments. Make sure you watch the pre-lab video for guidance on this part. If you only have one medicine dropper, make sure to clean it before dispensing another liquid. Use the table below to record the results of your experiments. 2 Water Baking Soda Baking Powder Cornstarch Detergent Cream of Tartar 5. Using baking soda, vinegar and a small plastic cup, determine if the amount of reagents you use affect the outcome of your observations. Please explain thoroughly your procedure and your conclusions.

5 6. Baking soda is also known as sodium bicarbonate while vinegar is a solution containing acetic acid, HC 2 H 3 O 2. Knowing this information, complete the following. a. Write the chemical formula for sodium bicarbonate. Note: bicarbonate is a polyatomic ion, HCO 3-1. b. Write a balanced chemical equation for the reaction of baking soda and acetic acid. The products of this reaction are carbon dioxide gas, water, and NaC 2 H 3 O 2. References: 1 From Dr. George Whitwell, Associate Professor of Chemistry at NCWC 2 Kessler, James, & Galvan, Patricia. (2004). Inquiry in Action: Investigating Matter Through Inquiry 2 nd ed., American Chemical Society.