Fizzy bubbly science Brief description Students observe the chemical reaction between vinegar (an acid) and sodium bicarbonate (a base). In small groups, they observe how bubbles of carbon dioxide gas produced by this reaction cause popcorn kernels to float and sink in water. They blow soap bubbles, which float on an invisible layer of carbon dioxide inside a soft drink bottle. As an optional extension activity, they can make fizzy edible sherbet. Duration: 60 – 80 minutes Year Level: Lower to upper primary Topics: Chemical reactions, Acids and Bases, Liquids & Gases, Floating & sinking, Buoyancy, Density Preparation: 15 minutes Extensions: SCIENCE – Make sherbet (included in student worksheet) SCIENCE – Research carbon dioxide (eg composition of the Earth’s atmosphere, sources of CO2, pollution, greenhouse effect) ART/SCIENCE – Construct an erupting model volcano with play-dough or paper mache Overview Whole class Teacher demonstration (5 – 10 min) Discuss procedure and safety instructions Designate group work jobs Small groups Activity 1 – Make and investigate pop-corn lava lamp (30 – 45 min) Activity 2 – Floating bubbles Whole class Discuss activities (5 – 10 min) Plan next science lesson Materials and equipment NOTE: Two 500g packets of Sodium Bicarbonate (baking soda) and one 2 litre bottle of vinegar should be sufficient for all the activities and teacher demonstration combined. Teacher Demonstration Total Qty Description 1 390 or 600 ml soft drink bottle 1 Balloon 1 Funnel * 3 Tbsp sodium bicarbonate ½ Cup vinegar * cut the top off a soft drink bottle to make a funnel if necessary Lesson 4 – Fizzy Bubbly Science Page 1 abc.net.au/science © Ruben Meerman 2004 Materials and Equipment continued … Total Qty Description 30 student worksheets (1 per student) 3 pages – download separately and photocopy 18 Clear plastic cups and/or glasses (1 per group) 6 1 litre soft drink bottles (tops cut off)1 (1 per group) 6 Small bubble blowers and solution 2 (1 per group) 6 Tablespoons (1 per group) 6 Teaspoons (1 per group) 1 packet Un-cooked pop corn (1 tbsp / group) 2 × 500 g Sodium bicarbonate ( ¾ cup / group) 2 litre Vinegar (1 cup / group) Water (1 cup / group) Sherbet ingredients and materials 75g Citric Acid 3 2 packets Flavoured jelly crystals 4 1 packet Pure icing sugar 6 Small plastic bowls or plates 1 – 6 Sieve(s) 30 Small plastic bags or similar to store sherbet 1 cut tops off with a utility knife prior to the lesson 2 students may be able to bring this item from home or you can make them easily – alternatively, ‘wedding bubbles’ are readily available from most supermarkets including solution and blower 3 available in baking section at supermarkets 4 note: jelly crystals are not suitable for vegetarians Preparation Materials for teacher to collect: y Sufficient quantities of plastic cups, bubble mix and blowers, popping corn, vinegar and sodium bicarbonate (bi-carb soda), spoons y Download and photocopy 30 student worksheets y Making sherbet: citric acid, flavoured jelly crystals, icing sugar, bowls, sieve(s) Materials for students to collect: y Empty 1 litre soft-drink bottles (minimum of 6 required for lesson) y If available at home – small bubble blower and solution Lesson 4 – Fizzy Bubbly Science Page 2 abc.net.au/science © Ruben Meerman 2004 Objectives You should check the outcomes statement for the year level of your class before deciding which of the following objectives are appropriate. Accurately describing and explaining the observations in these activities requires the synthesis of several scientific concepts. This may take different amounts of time for individual students. Asking questions about each concept in isolation may help students arrive at the correct explanation for their observations. Students’ prior knowledge Students are familiar with their group work job responsibilities. No prior knowledge of scientific concepts is assumed for this lesson. Positive attitudes Students will: y work cooperatively in small groups y ensure each member has an opportunity to see and understand the activities y handle equipment and materials carefully and responsibly y use water sparingly and dispose of waste responsibly (eg pour onto school garden beds, not into sinks) Science skills Popcorn Lava Lamp Activity Students will: y follow the instructions accurately y measure the required amounts of sodium bicarbonate and vinegar y observe the formation of carbon dioxide bubbles in the solution y observe that these bubbles adhere to the popcorn pieces y observe that the popcorn pieces float when covered with bubbles y observe that the bubbles pop when the popcorn reaches the surface, causing the pop corn to rotate y observe that the popcorn sinks after the bubbles have popped y describe their observations in writing and with illustrations Catch-A-Bubble Activity Students will: y follow the instructions accurately y measure the required amounts of sodium bicarbonate and vinegar y carefully blow bubbles and gently move the bottle to catch them y observe that the bubbles float on the invisible layer of carbon dioxide y infer that carbon dioxide is a heavier (more dense) gas than air Lesson 4 – Fizzy Bubbly Science Page 3 abc.net.au/science © Ruben Meerman 2004 Objectives continued … Science concepts y vinegar is a type of acid y sodium bicarbonate is a type of base y acids and bases undergo a chemical reaction when mixed together y one of the products of the vinegar and sodium bicarbonate reaction is a gas called carbon dioxide y carbon dioxide gas is less dense than water (it floats in water) y popcorn kernels are more dense than water (they sink in water) y air is less dense than carbon dioxide gas – air floats on carbon dioxide / carbon dioxide sinks in air Procedure Introduction (Whole class / 5 – 10 min) y Perform the teacher demonstration (see teacher notes on page 5) y Discuss the activities and give instructions for how you expect students to collect materials from the science store to prevent spills, you may wish to distribute the vinegar and sodium bicarbonate to each work station once the groups have collected all the other materials and are ready to begin y Allocate group work jobs and badges Hands-on activities (Small groups / 30 – 45 min) Small group activities y All group members cooperate to prepare a work station y All group members read the worksheet instructions y Equipment Managers collect materials required from Science Store f y Group Communication Officer asks teacher to deliver vinegar and sodium bicarbonate to work station (if not collected by Equipment Managers) y Group Supervisors ensure group adheres to instructions and completes activities y Records Officers keep careful notes of results where necessary y Equipment Managers clean and return equipment to the Science Store y Remainder of group cleans Work Station and returns desks to normal locations Early finishers y These activities are fun and visually stimulating so early finishers are likely to enjoy extra time to repeat the activities Lesson 4 – Fizzy Bubbly Science Page 4 abc.net.au/science © Ruben Meerman 2004 Conclusion (Whole class / 10 – 15 min) Class discussion y Conduct a discussion about the activities Plan next science lesson y Ask students to collect and bring in any household items you might require for the next lesson you have planned Teacher notes Teacher demonstration This demonstration will engage and motivate students. It provides clear visual evidence that gas is produced when vinegar and sodium bicarbonate react. Because students enjoy watching experiments, you can perform the entire set up (i.e. filling the balloon and bottle) as part of the demonstration. 1. Pour ½ a cup of vinegar into the empty soft-drink bottle using a funnel 2. Pour 1½ tablespoons of sodium bicarbonate into the uninflated balloon 3. Carefully stretch the mouth of the balloon over the mouth of the bottle making sure the sodium bicarbonate stays in the balloon 4. Lift and shake the balloon so that all the sodium bicarbonate pours into the bottle and let go of the balloon – the balloon will quickly inflate with carbon dioxide gas produced by the reaction Before ingredients are mixed After ingredients are mixed Description of the chemical reaction When an acid and a base react, they typically form a “salt” and water. In this reaction, vinegar is the acid (acetic acid) and sodium bicarbonate is the base. The products of the reaction are sodium acetate (the “salt”), water and carbonic dioxide. In chemical notation, the reaction is stated as: HC2H3O2 + NaHCO3 Æ NaC2H3O2 + H2O + CO2 Acetic + Sodium Æ Sodium + Water + Carbon Acid Bicarbonate Acetate Dioxide Lesson 4 – Fizzy Bubbly Science Page 5 abc.net.au/science © Ruben Meerman 2004 Description of the popcorn motion Popcorn kernels are only slightly more dense than water. The combination of a corn kernel and gas bubbles is less dense than water and therefore buoyant. When the reaction begins producing carbon dioxide bubbles, the kernels start to float. Once the corn reaches the surface, the bubbles at the top of the kernel burst. The bubbles attached to the bottom of the kernel now cause it to rotate. Once these remaining bubbles have burst, the kernel sinks again and the process is repeated. The diagram below illustrates the motion of a corn kernel. 3. Bubbles on top of kernel 4. Kernel spins, remaining pop bubbles pop ` 2. Bubbles make the kernel 5. After bubbles have float popped, kernel sinks 1. Bubbles form on kernel 6. Process starts again Motion of a popcorn kernel Catch-A-Bubble: why do the bubbles grow as they sink? You may notice that the bubbles in this activity grow as they slowly sink further into the layer of carbon dioxide. This happens because the concentration of carbon dioxide is much greater outside than inside the bubble.