Balloon powered car

Students send a message nobody can see, using only baking soda solution, turmeric and paper. They predict what could make a hidden message appear, plan what to hide, then write with a cotton bud dipped in baking soda solution and let it dry until it disappears. When they brush turmeric solution over the paper, the message appears in reddish-brown. Along the way, they discover that turmeric is a natural pH indicator that changes color when it meets a base, a hands-on lesson in indicators and acids and bases.