Differentiation Modifications Have students figure out that BTB is an indicator for CO2 by having them compare what happens to blue BTB when they blow bubbles in BTB through a straw, compared to making bubbles with a turkey baster. Ask students what the difference is between the air they exhale and the air in the bubbles from the turkey baster. Tips Collect results from the different groups and compare their measurements. Discuss threats to accuracy of measurement. Make sure that each student in every group has a chance to find the mass of something on the digital scales. Extending the Learning If students have questions about how or why the BTB changes color, show the first 6.5 minutes of the Colorful Indicators: MIT Chemistry Behind the Magic video (https://www.youtube.com/watch?v=nAhIrh9vM4A&t=2sO). This video provides an accessible explanation as to why CO2 causes the BTB to change color. Have students see how long it takes the BTB to change colors for a resting student and for that same student after exercising. Have students weigh other objects and use BTB to look for evidence of CO2 (or other acidic materials) in other liquids.