If your seal isn't tight around the top of the bottle, your balloon may fly off like a rocket into the air, so watch out!May 12, 18 · Vinegar is the acid and baking soda is the base This reaction between the two causes a gas called carbon dioxide to bubble and foam This gas having nowhere else to go, expands the balloon making the selfinflating balloon happen Want More Baking Soda andMay , · Using a funnel to add the baking soda to your balloon balloon Pour the vinegar into the bottle Carefully fit the balloon over the bottle opening, but do not drop the baking soda into the vinegar yet Once the balloon is completely over the cap, hold up the balloon and allow the baking soda to fall into the vinegar Baking Soda And Vinegar Balloon Experiment Balloon white vinegar bicarbonate of soda