Lab: Properties of Elements

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Lab: Properties of Elements

Properties of Ionic and Covalent Bonds

Problem: How are the properties of Ionic and Covalent bonds similar and different?

Standards:

  1. 8th Grade Science Standards: Each of the more than 100 elements of matter has distinct properties and a distinct atomic structure. All forms of matter are composed of one or more of the elements. As a basis for understanding this concept. b. Students know that compounds are formed by combining two or more different elements and that compounds have properties that are different from their constituent elements. c. Students know atoms and molecules form solids by building up repeating patterns, such as the crystal structure of NaCl or long-chain polymers. 7. The organization of the periodic table is based on the properties of the elements and reflects the structure of atoms. As a basis for understanding this concept. c. Students know substances can be classified by their properties, including their melting temperature, density, hardness, and thermal and electrical conductivity.

Materials:

  • Stations with the following materials: distilled water, salt, vegetable oil, detergent, hydrogen peroxide, orange juice, vinegar, sugar, baking soda, 2 small beakers, small jar with a tight fitting lid, small plastic spoon, graduated cylinder 100mL, heavy pot, hot plate, wooden spoon, Conductivity apparatus: 5-volt battery, a light bulb mounted station, and three pieces of insulated copper wire to make an open circuit (the circuit will be closed with each of the unknown samples), two pieces of naked copper wire, Safety goggles, Gloves

Procedure:

Stations

1. Before beginning experiment, read problem, materials, procedures and safety handout at each station. Put on required safety gear, copy any charts or questions into a separate sheet of paper. Complete all questions for each station. Students will have 10 minutes at each station. Students need to bring a pencil or pen, paper, activity sheet, and science journal to each station. Students need to rotate to the next higher numbered station when the whistle is blown. Groups at station six will rotate to station 1.

Station 1: Can Water and Oil Mix? (Page 192, Standards Warm –up)

1.Pour water into a small jar. 2. Add an equal amount of vegetable oil to the jar. Cover the jar tightly. 3. Shake the jar up and down for 20 seconds. Observe the water and oil. 4. Allow the jar to sit for 1 minutes. Observe again. 5. Remove the top and add 3 drops of liquid detergent. Cover the jar and repeat steps 3 and 4. 6. Based on your observations, write an operational definition (Operational Definition identifies observable conditions or events) How does your observations relate to chemical bonds in the detergent, oil and water molecules?

Station 2: Comparing Molecular and Ionic Compounds (Page 195, Math Analyzing Data)

1. Study a bar graph of the melting points in the comparison table. Notice the bars are ordered by increasing melting point. (The y-axis begins at -200 degrees Celsius and goes to 900 degrees Celsius). 2. Interpreting Data: Describe what the graph tells us about the melting points of molecular versus ionic compounds. 3. Inferring: What causes these differences between molecular compounds and ionic compounds? Interpreting data: How do the boiling points of the molecular and ionic compounds compare? (List at least two similarities and two differences)

Station 3: Comparing and Contrasting Ionic compounds

1. Compare and contrast ionic compounds. Observe Table Salt (NaCl) and Baking Soda (NaHCO3). Observe color, hardness, malleability and texture. Draw a picture of each compound. What is different: (Make three observations. What is similar about the compounds? 2. Infer: What do you think is a property of ionic compounds in general?

Station 4: Melting points of Ionic Compounds

1. Place salt in a pot and heat on high. After 5 minutes observe if salt has melted. Record temperature of salt every minute and record in a table. Table has time in minutes and observation columns. 2. Answer questions: Why does salt have a high melting point?

Station 5: Polar Molecules

1.Fill a clean beaker with water and another with an unknown liquid. Float a small sewing needle horizontally on the surface of each beaker. 2. Answer the following questions: What is this property of liquids allows the needle to float? Why does one liquid support the needle while the other does not? What type of attraction between molecules does this represent?

Station 6: What kind of compounds produce Ions in solution?

1. Draw the data table in your science journals. The table has sample and observations columns. 2. Make a conductivity tester and connect conductivity probes. 3. Pour 50 mL of tap water into a small beaker. Put the bare copper wires with the conductivity apparatus attached into the water. Do not let them touch! Record your observations. (Does the bulb light?) Repeat the steps for Distilled water, Sodium Chloride, Sodium Chloride and water, vegetable oil, hydrogen peroxide, orange juice, sugar, and sugar and water. 4. Add another column to your table: Ions in solution. Does the sample produce ions in solution and conduct electricity? (Does the bulb light?) 5. Answer the questions: Why are there differences in conductivity between dry and dissolved sodium chloride? Based on your observations, is sucrose (table sugar) made up of ions? Explain?

Clean Up:

Each station must be cleaned and left in original condition. Make sure to put all materials back in their containers. Wipe down table if needed.

Conclusion: Complete the following Venn Diagram with your table group. Compare and contrast Ionic and Covalent bonds. If you need more room, copy the diagram onto a separate sheet of paper. Also, fill in all blanks at the bottom of the worksheet.

Fill in the Blanks:

Ionic compounds and molecular compounds are similar because ______.

In Ionic compounds, atoms are joined by ______that are made when ______.

In molecular compounds, atoms are joined by ______which are made when ______

______.

These types of compounds have different properties. Ionic compounds______

______. Molecular compounds ______

______.