ShmoopTube

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And here's your Shmoop du jour, brought to you by baking soda.

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Its use in your bread is… on the rise. Okay, here's today’s question. [Bread expands out of microwave]

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In our bodies, we have a buffering system to keep our pH at a certain level. This buffering

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system uses carbonate and bicarbonate ions. What is the conjugate base of the bicarbonate

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ion, HCO3- in water?

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And here are your potential answers.

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Sodium bicarbonate is the active ingredient in baking soda, and it’s what causes bread [People scared of bread expanding from a microwave]

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to rise. Or to take over your oven and become some

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sort of crazy dough monster. Hypothetically… For this question, we need to consider the [Acid and Base appear at a table]

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acid-base chemistry of the bicarbonate ion.

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Specifically, we want to know the conjugate base of this species.

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Acids and bases react to form their conjugate partners. [Acid and base getting married]

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When an acidic species H A reacts with a base B by donating a proton, it becomes its conjugate

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base, A-.

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On the other hand, when a basic species B reacts with an acid H A by accepting a proton, [Base accepting proton]

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it becomes its conjugate acid, HB+.

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And then it goes to Starbucks for a pumpkin spice latte. [Base drinking a starbucks latte]

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Get it? Basic? Heh.

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Anyway, we need to know what happens when bicarbonate acts as an acid, and thus becomes [Bicarbonate jumping on a sofa]

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its conjugate base. To act as an acid, it must lose a proton.

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Don’t forget that when we split up this ionic species, we have to consider the resulting [Ionic species split in half]

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charges.

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Our entire bicarbonate species has a -1 charge. Our proton, H+, has a +1 charge.

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That means that the CO3 species must have a -2 charge, as the sum of the charge on this

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and the proton must equal the overall charge on the entire bicarbonate ion.

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So we can see that our conjugate base is CO32-.

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So C is the correct answer. And if you understood all that, then you definitely [Girl eating a cake]

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deserve some kind of baked good. We recommend cookies, but whatever floats

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your boat.

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