Procedure A makes a soda drink with orange juice and baking soda. The students find out where the bubbles come from. Good for all ages.
Procedure B compares the amount of bubbles made when baking soda is added to different juices. Students learn about acidity. Best for intermediates.
Procedure A. Make soda drink:
Fill a dixie cup with juice. Drink a little of it to see what it tastes like before the experiment.
Scoop up about 1/8 teaspoon of baking soda, using the coffee stir stick. Tip it into to the cup of juice and stir it in. Look carefully for tiny bubbles rising to the top of the liquid. Listen for bubbles popping on the surface (quiet is needed to hear them). Taste the juice again - the juice should be fizzy.
Discuss the state changes during this chemical reaction: a liquid and a solid produced a gas. The gas bubbles stayed in the liquid, to make the drink taste fizzy.
The specifics of the reaction can be discussed: the bubbles are carbon dioxide, formed by the chemical reaction between an acid (the juice) and a base (the baking soda).
Optional for younger students: students can use molecule models to show the reaction:
Give students molecule models of the molecules in baking soda and orange juice. Ask them to figure out the new molecules that are made when the baking soda and orange juice mix, by taking apart these molecules and rearranging the atoms to make new molecules. Give them a hint that one of the new molecules is water (show a model), and ask them to use up all the rest of the atoms and bonds to make the other molecule.
HCO3 (baking soda) + H (orange juice) —> H2O (water) + CO2 (carbon dioxide gas)
See the molecule photo above. Note that the CO2 molecule has two double bonds - students may need prompting to fill up all the holes in the atoms to complete this molecule.
Once all students have made their water and CO2 molecules, name the carbon dioxide molecule and ask if students have heard of it. Tell them that it is a gas, and this is what makes their soda drink fizzy.
The chemical reaction they just modelled, is the same as what is happening when they make orange juice and baking soda to make their soda drink.
Further discussion on soda drinks and acidity:
Canned sodas are fizzy because they have carbon dioxide gas in them. Soda fountains inject carbon dioxide gas into drinks.
Anything that has free H atoms (ions) is acidic and tastes sour. The more sour it tastes the more H ions it has e.g. lemon juice has more H ions than orange juice. We add sugar to drinks to mask the sour taste.
Procedure B. Make soda drink, then compare different juices:
Start by making a soda drink with orange juice, as in Procedure A.
Students use molecule models to figure out the chemical reaction that made the bubbles of gas:
Give them the starting molecules, and ask them to rearrange the atoms and bonds to figure out what molecules are made (given them a hint that one of the end molecules is water).
HCO3 (in the baking soda, or base) + H (in the juices) —> H2O (water) + CO2 (carbon dioxide gas)
See the molecule photo.
Then compare different juices for how many bubbles they make with baking soda:
Give student group squeezy bottles of the juices, 15ml tubes in a rack (one tube for each juice type), baking soda in a pot and several stir sticks.
Students label each tube with each juice type, then add the same amount of each juice to each labelled tube (try 5ml; 7ml overflows on lemon juice).
Add the same amount of baking soda to each juice (make best guess at scooping the same amount onto the stir stick each time), and quickly stir the baking soda in before removing the stick. Use the numbers on the tube to record where the bubbles rise to for each juice type (worksheet attached for recording results).
Tabulate/graph the class results, and rank the juices by how many bubbles they make. There will be variation between the groups, but that is expected with real data collection.
Take the most common ranking of juices among the groups for class discussion:
Why does each juice make more or less bubbles?
Refer to the chemical reaction again: some juices have fewer H atoms in them, so when baking soda is added, they make fewer CO2 molecules. Therefore fewer gas bubbles are made. Juices with more H atoms in them can make more CO2 molecules, so make more bubbles of gas.
The number of H atoms in a juice determines how acidic it is, which is the same as how sour it is.
So fewer H atoms means less acidic and less sour. And more H atoms mean more acidic and more sour.
Which juice would you predict is the most sour? (The one with the most bubbles, as it would have more H atoms.)
Students can taste each juice to test if the juice with the most bubbles is also the most sour. Lemon juice will certainly be very sour, and apple juice not sour. A complication is that sugar is added to juices to offset the sourness, so cranberry juice, which is very acidic, and will make lots of bubbles, may not obviously taste the most sour. Students may be able to detect the sourness of cranberry juice behind the sweetness.
Students are free to make one more soda drink from the juice of their choice.