Practical No. 1

[AnnabelleBuda]

Testing Practical No. 1 (Bath Bombs)

https://www.scientificamerican.com/article/sudsy-science-creating-homemade-bath-bombs/ https://www.scientificamerican.com/article/build-a-balloon-powered-car/

1. Make bath bombs/ fizzy bombs.
2. Capture carbon dioxide gas from bath bombs in balloons.
3. Measure difference in weight due to loss of carbon dioxide in the reaction.

Making the bath bombs:

The bath bombs were made by mixing together cornstarch (11 g), citric acid (11 g) and sodium bicarbonate (22 g). The wet ingredients vegetable oil (1 tsp), water (1 tsp) and red food colouring (2-3 drops) were mixed together separately. The wet ingredients were then added to the dry ingredients, dropwise with mixing to prevent the citric acid and sodium bicarbonate from reacting during this step. The resulting mixture was a soft, doughy consistency which was then packed tightly together and left to dry for 1-2 hours. This was repeated with cornstarch (12.5 g), citric acid (12.5 g) and sodium bicarbonate (25 g). If the mixture of wet and dry ingredients is too dry, the mixture will crumble and not pack together.

Figure 1: Completed bath bomb after drying for 1 hour.

Capturing the carbon dioxide gas:

Figure 2: Apparatus for carbon dioxide capture from the bath bomb reaction.

One of the dry bath bombs was placed into a beaker with a plastic funnel sealed over the top using parafilm. A balloon was placed over the top of the funnel and held in place with a rubber band and parafilm (Figure 2). Water was added prior to sealing the vessel with the parafilm.

There was some inflation of the balloon, however it is likely that the parafilm did not adequately seal the beaker. Also, the beaker was likely too large to create the pressure needed for the balloon to expand. A smaller balloon might also help this issue.

In order to proceed to the next part of the practical (using the carbon dioxide to propel a mini vehicle):

• A larger bath bomb will have to be used (or multiple bath bombs combined)
• A smaller container should be used for the reaction
• A more airtight container is necessary
• A smaller balloon may help

Weighing the solution before and after the reaction:

The other dry bath bomb was weighed. A beaker of water was weighed separately and the mass of each recorded and added together. The bath bomb was then placed in the beaker of water and allowed to fully react. The final mixture was then weighed again and the difference between this weight and the added weight of the bath bomb and beaker of water was calculated.

The bath bomb initially weighed 50.54 g while the beaker of water weighed 282.95 g, giving a total of 334.49 g. However, after the reaction the combined bath bomb and beaker of water weighed only 331.66 g, giving a difference of 2.83 g. This should be a great enough difference to be measured on kitchen scales which would be accessible in a primary school, though it should be repeated to ensure the difference is from escaped carbon dioxide and not just from loss of water due to bubbling out of the beaker or crumbling of the bath bomb placing it into the water.

Apart from some minor changes, this practical looks feasible for a primary school experiment. The making of the bath bombs should not take more than 20-30 min. The drying of the bath bombs is not completely necessary for the experiment, so it can either be split over two days or performed with still wet bath bombs in under one hour.

[AnnabelleBuda]

Retesting carbon dioxide capture with balloons

Previously, the beaker used for holding the reaction was too large. The reaction was repeated in two other vessels; a test tube with a side arm and a vacuum flask. Smaller balloons (water balloons) were also tested, in case the amount of pressure produced was not enough to fill a regular balloon.

Figure 3: Carbon dioxide capturing using a test tube and balloon.

The a 50 mL test tube was used, and a water balloon was attached to the side arm and secured with parafilm (Figure 3). Because of the size of the test tube, a large bath bomb would not fit, so citric acid (6 g), sodium bicarbonate (12 g) and cornflour (~5 g) were mixed in the test tube. Water was then added and the test tube quickly sealed with a cork. The balloon expanded, however there was some overflowing of the test tube. The regular balloon was too large to secure to the test tube side arm with an adequate seal.

Figure 4: Carbon dioxide capture using a vacuum flask and a balloon.

The reaction was repeated in a 250 mL vacuum flask (Figure 4). The balloon was secured to the sidearm with parafilm and the bath bomb and water placed through the top of the flask. The flask was then quickly stoppered with a rubber stopper to prevent the escape of carbon dioxide. This procedure expanded both the regular balloon and the water balloon with no spillage.

[AnnabelleBuda]

Teachers Information Sheet

This practical seeks to address aspects of the Working Scientifically and Material World sections of the syllabus. In this experiment, students will cover the following syllabus dot points:

• observe and compare the differences in the properties and behaviour of solids and liquids, eg shape and ability to flow.
• demonstrate that air has mass and takes up space, eg in an inflated basketball, bubbles, balloons and beaten egg white.
• observe some irreversible changes that common materials undergo to identify that the changes may result in new materials or products, eg rusting iron, burning paper, cooking a cake and making toffee.
• classify some observable changes that materials undergo as reversible or irreversible.
• research the reasons for and the benefits of using solid, liquid and gaseous fuels for heating.

NSW K-10 Science Syllabus

Equipment List:

Bath-bomb Ingredients

• Cornstarch
• Citric acid
• Sodium bicarbonate
• Water
• Vegetable oil
• Food colouring
• Baking molds/ plastic cups
• X2 bowls for mixing

Capturing/ measuring carbon dioxide

• Balloons
• Vacuum flask
• Kitchen scale

Mini vehicle

• Plastic bottle
• Straws
• Bottle caps
• Tape
• Scissors
• Wooden Skewers

Worksheets

• Teacher information sheet
• Student activity questions and instructions

Method:

For one bath bomb:

1. Combine 1 heaped tablespoon cornstarch, 1 1/3 third tablespoons citric acid and 2 2/3 tablespoons sodium bicarbonate in a bowl and mix well.
2. Combine the 1 teaspoon of water, 1 teaspoon vegetable oil and 1-2 drops food colouring in a separate bowl/cup and mix well.
3. Add the wet ingredients to the dry ingredients slowly and dropwise. Stir the mixture when it fizzes and don’t add too fast. You may not need to add all the wet ingredients! The final mixture should not be powdery anymore.
4. Spoon the mixture into the baking mold, pressing down as you go. Make sure it is pressed down very firmly.
5. Leave the bath bomb to dry overnight/ for a few hours.

Part A (Propelling a mini vehicle with gas):

1. Make your plastic bottle car.
2. When the bath bomb is dry put it in a vacuum flask.
3. Attach a balloon to the side arm of the flask.
4. Add water to the bath bomb through the flask opening and quickly seal the flask with a rubber stopper.
5. Watch the balloon fill up as the bath bomb dissolves.
6. When the balloon is fully inflated, or when the solution in the flask stops bubbling, pinch the balloon shut before removing it.
7. Keeping the end pinched shut, attach the balloon to the straw on the plastic bottle car.
8. Release the balloon to start the car.

Part B (Does gas have mass):

1. On a kitchen scale, weigh a jar of water. Record the weight.
2. Weigh a bath bomb and record the weight.
3. Add together the two weights you have recorded.
4. Put the bath bomb you weighed into the jar of water and wait for the solution to stop fizzing.
5. Weigh the jar of water that now contains the dissolved bath bomb.
6. Calculate the difference between the weight you calculated of the bath bomb and the jar of water and the measured weight of the two combined.

Background Information:

In the making of the bath bombs, the students will be working with solids in the form of powders. These will then be combined together to form a compact ball. The students may be asked if the materials are undergoing a change of state at this point. Though there is no change of state occurring, the changes in the properties of the solid bath bomb as it goes from mallerable to brittle are interesting to note. This is a good demonstration of how solids may have different properties and yet still be considered solids.

The reaction of the bathbomb in water is an acid-base reaction in which the citric acid reacts with the sodium bicarbonate to form sodium citrate, water and carbon dioxide. This is an irreversible change that takes place as molecules are rearranged to form new molecules. Students should take care to observe and record the changes as the bathbomb is dissolved in the water and to note any features that they see (e.g. bubbles, the water taking on the colour of the bathbomb, the balloon expanding etc.).

Some questions to consider at this point are:

• Is the dissolving of the bath bomb a reversible or irreversible change? If the students consider it a reversible change, ask them how they would go about getting the bath bomb back out.

The bath bomb reacting in the water is an irreversible (chemical) change. The water dissolves the solids into very tiny particles (molecules), so they can react together, rearranging to form new particles. One of these new particles is a gas which takes up more space and so fills up the balloon.
If you were to evaporate the water to retrieve the solid from the water, it would not be the same solids (sodium bicarbonate and citric acid) that you started with. Instead you would have sodium citrate.

• If you put a solid into the water, where is the gas coming from that is filling the balloon?

The gas is a product of the chemical reaction of sodium bicarbonate and citric acid. It is important for the students to understand that even in an irreversible change nothing is being “created” in the reaction vessel that was not already there. The new gas is simply from matter being rearranged, not created.

• Does gas/air have mass?

Put it to a class vote, hands up for gas has mass, hands up for gas doesn’t have mass. If it doesn’t have mass, then how can it take up space and fill up the balloon? Do gases have volume? Use the balloon expansion to explain that gases do have volume and take up space. By calculating the difference between the total weight of a glass of water plus a bath bomb and the weight of the glass of water after the bath bomb has reacted in it, the students can discover that the gas released has mass. Ask the students why one is heavier than the other when they should contain the same materials.

• Why does the car move forward when the gas is released?

The pressure of the gas is forcing the balloon to expand. When the balloon is opened the potential energy from this pressure has an outlet and the gas is pushed out of the high pressure environment of the balloon to the low pressure environment of the outside air. This is a similar process to how wind is created as in the high and low pressure systems in weather; air moves from areas of high pressure to areas of low pressure.

• Is the propulsion of the mini-car the same way a real car moves?

Ask the students to list examples of ways that real-life vehicles move and compare them to the balloon propelled mini-car.

• How do we know the air inside the balloon is not oxygen/ breathable air?

Ask the students to list ways to test whether or not the gas inside the balloon is oxygen/ breathable air. You may choose to demonstrate that the gas in the balloon is carbon dioxide by pouring a container with the gas over a lit candle to extinguish it. This would also be a prelude for the discussion that gases, like liquids and solids, can have different densities and carbon dioxide is more dense that the air we breath, so it “pours” (or sinks) below the air.

Troubleshooting:

• If the balloon does not expand, it is likely that the container is not properly sealed. Seal any unsealed areas with blu-tack. If this does not work, add additional citric acid and sodium bicarbonate to the container (1 teaspoon of each). You may ask the students why they think the balloon is not expanding.
• To prevent fizzing while the liquid ingredients are added to the dry ingredients in making the bath bombs, add the wet ingredients slowly and stir the mixture thoroughly each time.
• If the bath bombs are too brittle, add more of the wet ingredients for next time.
• Make the bath bombs over a piece of paper so that even if they crumble, you can still use the ingredients and react them with water.

[AnnabelleBuda]

Student Reflection Sheet

After experiment and collecting results:

1. In this experiment, you have observed solids, liquids and gases. What do your observations lead you to conclude about their properties?
2. Which changes that you observed are irreversible and which (if any) are reversible? How do you know?
3. In this experiment, you observed a gas inflating a balloon. Where did this gas come from?
4. You weighed the water and the bath bomb separately and then again after they had been mixed together. What did you notice about the weight?
5. Give a possible reason for your observations.
6. Combine your class results to find the mean difference in weight for the reaction.

[AnnabelleBuda]

Student Inquiry Sheet

Before experiment, after reading method:

1. Before you begin, do you think the reaction when the bath bomb enters the water will be a reversible or irreversible change? Give a reason for your answer.
2. You will be taking some measurements and comparing them. What needs to be the same across the whole class for it to be a fair test?
3. What do you think will happen to the balloon when the bath bomb is submerged in water?
4. How would you be able to measure whether or not gas has mass?
5. Suggest a way to tell whether or not the gas in the balloon is breathable air (contains oxygen) WITHOUT breathing it in.
6. What are some things you could change to test other ideas?

[AnnabelleBuda]

HIRAC.docx