Dissolved Oxygen By: Lorinda Rogers

Transcription

1 Dissolved Oxygen By: Lorinda Rogers

2 Grade: 8 th Introduction to Chemistry and Physics Learner Goals and Academic Expectations: *Goal 2- Students develop their abilities to apply core concepts and principles from science to what they encounter throughout their lives. 2.1 Students understand scientific ways of thinking and working and use those methods to solve real-life problems 2.2 Students identify, analyze, and use patterns such as cycles and trends to understand past and present events and predict possible future events. 2.3 Students identify and analyze systems and the ways their components work together to affect each other. *Goal 6 Students develop their abilities to connect and integrate experiences and new knowledge from what they have previously learned and build on past learning experiences to acquire new information. 6.3 Students expand their understanding of existing knowledge, by making connections with new knowledge, skills and experiences. Program of Studies: Scientific Inquiry and Scientific ways of Thinking and Working: *conduct different kinds of scientific investigations for a wide variety of reasons. *Use equipment, tools, techniques, technology and mathematics to improve scientific investigations and communications. Chemical Reactions: *Investigate chemical reactions.

3 *Investigate factors affecting reaction rates. Objectives: Students will. *Learn the meaning of dissolved oxygen *Learn that solubility of gases increases with increasing pressure and decreases with increasing temperature. *Understand the relationship between dissolved oxygen and aquatic life in a waterway. *Learn what factors may deplete the amount of dissolved oxygen in a waterway. *Determine the amount of dissolved oxygen of a river and use dissolved oxygen data to determine water quality. What is Dissolved Oxygen? ACTIVITY ONE: Have students research the meaning of dissolved oxygen by reading: ML And completing the vocabulary. Discuss. Vocabulary: atmosphere, percent saturation, dissolved oxygen, pressure ACTIVITY TWO: Students complete investigating the Solubility of Gases activity. Materials: Safety goggles 500ml beaker 100ml graduated cylinder heat source triple beam carbonated beverage, precooled paper toweling stop watch Celsius thermometer

4 Purpose: To observe the effect of pressure and temperature on dissolved carbon dioxide. Background: In this activity, students will investigate the effect of pressure and temperature on the carbon dioxide dissolved in a can of carbonated soda. Carbonated beverages are canned or bottled under several atmospheres of pressure of carbon dioxide gas, so the liquid in each can will dissolve more carbon dioxide gas than it would at just one atmosphere. When you remove the tab or cap from a carbonated beverage, you can see and hear the excess carbon dioxide gas escaping. Carbon dioxide gas escapes from the beverage until it reaches its normal solubility level at one atmosphere of pressure. Procedure: A. Pressure and Solubility 1. Using a graduated cylinder, measure 100ml of water. Pour the water into a 500ml beaker, and place the beaker on a heat source until its temperature reaches 50 degrees Celsius. 2. While the water is heating, dry the outside of a cooled, unopened can of soda. 3. Find the mass of the can of soda and record in Data Table Carefully open the can and allow the excess carbon dioxide gas to escape. (This will take about 3 minutes) 5. Weigh the can and record its mass. Repeat this step every three minutes until 15 minutes have elapsed. Check the beaker of water periodically to make sure it has not overheated. B. Temperature and Solubility 1. Measure the temperature of the opened soda can and record the temperature in Data Table2. Measure the temperature of the heated water to make sure that it is 50 degrees Celsius. 2. Place the opened can in the 500ml beaker that contains the heated water. Allow the can to warm for 10 minutes. Turn off your heat source. 3. Record the temperature of the liquid inside the can 4. Remove the can from the hot water. Dry the outside of the can. 5. Find the mass of the can, and record its mass in Data Table 2. Calculations: 1. Calculate the grams of carbon dioxide lost from the heated, opened can and record in Data Table 1. (Initial mass of opened can mass of can heated for 10 minutes= mass of carbon dioxide lost)

5 2. Calculate the number of grams of carbon dioxide lost after 15 minutes as the internal pressure of the can was reduced to atmospheric pressure. Record in Data Table 2. (Mass of unopened can mass of opened can after 15 minutes = mass of carbon dioxide lost) Analyses and Conclusions: 1. Explain why the opened can of carbonated beverage weighed less after 15 minutes. 2. What do you think would happen if you let the opened can stand overnight? 3. What effect did a rise in temperature have on the mass of the carbonated beverage in the opened can? Explain this result. Critical Thinking Questions: 1. One summer morning, some teenagers bought several cartons of soda to take to the beach. They put the soda in the trunk of their car but then forgot to take it out until late afternoon. When they opened the trunk, they found that the cans had burst and soda was everywhere. Propose a hypothesis for why this happened. 2. Marita and Joe went fishing one hot summer day. Marita let her fishing line hang several meters deeper in the river than Joe. Marita caught her limit of fish. Joe caught only one catfish. Offer a hypothesis as to why Marita caught more fish than Joe.

6 Time (minutes) Mass (grams) Amount of Carbon Dioxide Lost= grams Time Temperature(Celsius) Mass (grams) Initial time: After 10minutes Amount of Carbon Dioxide Lost = grams

7 ACTIVITY THREE: Students take a field trip to a river to collect water samples and measure the amount of dissolved oxygen. Students will then analyze results and determine if the river is safe for aquatic life based on the chart on the webpage. Materials: Dissolved oxygen test kit