How Does Double Acting Baking Powder… Doubly Act?

OK so I’ve got a clear liquid here… and
a different clear liquid here… and I’m going to add a white powder to this one — ooh,
bubbles — and then a different white powder to this one… Also bubbles, but different this time… Now while these are sitting around I’m going
to hop over here and get a water bath up to 75 degrees Celsius  
And now I’m going to take both of these — which have stopped bubbling — and put
them… in this water bath, and wait a few minutes for these to come up to temperature,
and… what….? Where are these bubbles  coming from? [splash]
Alright, so you’ve probably guessed that the liquid in this bowl was vinegar and that
the white powder was baking soda, so you also know the bubbles are carbon dioxide. In this bowl, the clear liquid was just plain
old water, and the powder was a mixture of baking soda, monocalcium phosphate, and cornstarch. You know this mixture as double acting baking
powder, and it’s quite different than that other white powder — baking soda. Here’s how. Baking powder contains at least one solid
acid. In this case, monocalcium phosphate. It also contains a solid base, almost always
baking soda. The acid and base react with each other when
water is added to produce carbon dioxide gas. But… we waited for this reaction to finish,
in other words we waited for all the acid and the base to react with each other… so… Where are these extra bubbles coming from? Well it turns out that the acid doesn’t
dissolve very much in water. So, while the baking powder is just sitting
here at room temperature, most of the acid doesn’t actually react with the base. Heat helps the acid dissolve more in water,
which means more of it will react with the baking soda, which means more CO2 is produced,
which means… more bubbles. There may also be other reasons heating makes
more CO2, depending on which baking powder you use, but that’s a long and convoluted
story involving Henry’s law and Le Chatelier’s principle… so we’ll cover that in another
video. With cookies next time. Mmm. Cookies. Anyway, this is where the “double acting”
thing comes from — it “acts” once out here in the batter, and then it “acts”
again in the oven. By the way, almost all baking powder sold
today is double acting. Thanks for watching, and if a chemistry question… bubbles up in your brain, let us know in the
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8 thoughts on “How Does Double Acting Baking Powder… Doubly Act?

  1. I miss Alton Brown's old show where he'd explain stuff like this… It's super interesting even though my cooking ability doesn't extend much further than ramen noodles

  2. How long does your survey go on for? I feel like I just did one a few months ago (2-4 months?). Is it the same survey, or is this a new one?

  3. So I enjoy pretty much all of your videos, but this one really stands out to me as a personal favorite! This has to be the most relaxing science video I have ever watched. I love the chill narration and smooth jazzy music in the background. Jazzy background music is hard to do right because sometimes it will draw too much attention to itself, but this selection was perfect. But most importantly, I learned something interesting. Please keep making these awesome videos!


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