Changes in States of Matter Involving Carbon Dioxide

8th Grade

Vanderbilt Student Volunteers for Science

Training Presentation

Fall 2013

Important!!!

• Please use this resource to reinforce your understanding of the lesson! Make sure you have read and understand the entire lesson prior to picking up the kit!

• We recommend that you work through the kit with your team prior to going into the classroom.

• This presentation does not contain the entire lesson—only selected experiments that may be difficult to visualize and/or understand.

Before you begin…

• Give each group two instruction sheets (contains thermometer diagram back to back with instruction sheet). You will still need to guide them through the procedures, and making sure they are completing the observation sheet.

• SAFETY NOTE: Students should not hold pieces of dry ice. The temperature of dry ice is -78° C, and students could get frostbite burns if their skin is in contact with dry ice for more than a few seconds.

• Students should use tongs to put dry ice into cups etc.

I. Introduction• Please refer to manual for detailed

explanations and descriptions.

A. Discuss the states of matter – solids, liquids and gases.

• There are 5 processes involved in changes of state (freezing, melting, vaporization, condensation and sublimation.

• Have students name the physical changes that lead to changes of state.

B. What is CO2? • Discussion of cold temperature of

dry ice

I. Introduction (Cont.)Demonstration: Freezing water with dry ice

•Pour some dry ice into the insulated container (wear gloves).

•Pour water to about 1 cm depth.

•Place cup in insulated container with dry ice and wait until the end of the lesson to show students the cup of water, which has now been changed into ice

II. Comparing Dry Ice to Water Ice• Give a plate, bags, tongs, ice and dry ice to

PAIRS. Remind students that they should not touch the dry ice.

• Tell students to use their tongs to put a piece of dry ice into a ziploc bag and regular (water) ice into the other bag and close the ziploc fastener.

• Ask the students to describe the appearance of the two types of ice and to observe both pieces of ice in the for a few minutes.

• Have students describe what happens and record their observations on the observation chart. What changes in states occurred?The dry ice ziploc bag will inflate because of the CO2 gas being given off by the solid.

II. Comparing Dry Ice to Water Ice

• Tell students to open the ziploc bags and carefully empty the pieces of dry ice and ice onto the aluminum pan.

• Tell students to leave the two pieces of ice on the aluminum pan, do not move them, but observe them periodically to see what happens over time.

• Compare the dry ice with the H2O ice and record observations .

– Water ice leaves a puddle, dry ice sublimes to a gas.

– “Smoke” comes off dry ice (water vapor in the air condenses around dry ice).

III. Observing Changes of State Using Dry Ice

• Give each pair a clear plastic cup that is about one-third full of “ocean” water.

• Show the students the universal indicator and tell them that it is used to measure the acidity of liquids. Have them look at the Universal Indicator chart.

• Tell students to:– add a squirt of universal indicator to the water and

observe the color. – add regular ice to the cup and ask them whether it

sinks or floats. – use their tongs and place a piece of dry ice into

the water. Does it sink? Start observing and record the color changes as soon as the dry ice is added to the cup.

– Record everything they observe and to record all the phase changes.

• Ask the students to share something they observed. Draw a picture of the cup (shown below) on the board and record the different observations from the students.

• Have the students identify the changes in the states.

III. Observing Changes of State Using Dry Ice (cont’d)

• Observations (see manual for explanations)

• Dry ice gives off bubbles when it is added to water.

• A white fog appears over the water in the top of the glass.

• The white fog stays in the top of the glass and any white fog that leaves the glass goes down along the side of the glass rather than up into the air.

• Fog that goes down along the glass disappears near the bottom of the glass.

• Universal Indicator turns red.• Dry ice sinks, regular ice floats.

IV. Discussion on the Effect of CO2 in Oceans

• Write on the board: carbon dioxide sink, acidification• Ask the students what they know about the effect of carbon dioxide on the

atmosphere? See manual.• Ask the students what they know about the effect of carbon dioxide on the oceans?

See manual.• Write the following equation on the board:

CO2 + H2O → H2CO3

Carbon dioxide water carbonic acid

• Water in the oceans can remove CO2 directly from the air.

– Oceans are called sinks for CO2.

• Ask students if they can think of consequences of dissolving increasing amount of carbon dioxide in ocean waters? (Ocean becomes more acidic).

– Acidification could adversely affect marine life. Corals and shells are composed of calcium carbonates which can dissolve in acidic water.

– CaCO3(s) + CO2(g) + H2O → Ca(HCO3)2 (aq)

V.CO2 as a Fire Extinguisher

• Make sure there are still a few pieces of dry ice into each group’s cup. Demonstrate the procedure.

• VSVS team members should light the candles and stay with the students while they do the next step. Do NOT leave a lit candle unattended.

• Tell the students to pick up the cup and pour out the gas (CO2) into the cup over the candle flame. This should extinguish the candle. VSVS members should then move to the next group.

• Ask students: Why does CO2 extinguish the candle? Why could we pour the CO2 into the cup? CO2 is heavier than air so it will stay in the cup?

VI. Finish Demonstration of Freezing Water with Dry Ice

• Remove the cup of water from the container of dry ice to illustrate how the dry ice can freeze water.

• Have the students note the phase changes. Liquid water freezes to solid ice water.

• Tell the students to look at their thermometer diagram to see that the temperature of dry ice is much colder that regular ice.

VII. Review

• Review the changes of state and ask the students to give examples from today’s experiments.

• What does sublime mean? A solid goes directly to a gas without becoming a liquid.

• What is dry ice? Solid carbon dioxide.• How cold is dry ice? -78°C. Refer to the thermometer

diagram.• What happens when dry ice is dropped into water?

Bubble of carbon dioxide are given off, a cloud forms above the water, the cloud stays in the container instead of floating in the air, if any of the cloud falls out of the container it floats down and disappears.