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Hadi Khan
Hadi Khan
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It's well known that if you put carbonic acid $\ce{H2CO3}$ into water it will dehydrate into carbon dioxide $\ce{CO2}$ and water $\ce{H2O}$. Indeed this is how modern fizzy drinks generate their fizz. Taking this as a given what I don't understand is why doesn't sodium bicarbonate dissolved in water not slowly give off $\ce{CO2}$ via the following pathway:

$$ \ce{HCO3- +H+ <=> H2CO3} $$ $$ \ce{H2CO3 -> H2O + CO2} $$

This would lead to the solution of sodium bicarbonate slowly converting itself into a solution of sodium hydroxide. The first part of the reaction is reversible and is something that at equilibrium will have a non-zero amount of $\ce{H2CO3}$ and. In fact given that carbonic acid is a weak acid there will be a lot of $\ce{H2CO3}$ present at equilibrium. I also can't see how the presence of sodium ions in solution would inhibit the second reaction (since that is the only difference between this solution and a solution of pure carbonic acid which does effervesce) so according to my understanding we should be seeing a fizz .

However very clearly this bubbling does not happen in real life, as anyone can easily verify for themselves. So what inhibits it then?

It's well known that if you put carbonic acid $\ce{H2CO3}$ into water it will dehydrate into carbon dioxide $\ce{CO2}$ and water $\ce{H2O}$. Indeed this is how modern fizzy drinks generate their fizz. Taking this as a given what I don't understand is why doesn't sodium bicarbonate dissolved in water not slowly give off $\ce{CO2}$ via the following pathway:

$$ \ce{HCO3- +H+ <=> H2CO3} $$ $$ \ce{H2CO3 -> H2O + CO2} $$

This would lead to the solution of sodium bicarbonate slowly converting itself into a solution of sodium hydroxide. The first part of the reaction is reversible and is something that at equilibrium will have a non-zero amount of $\ce{H2CO3}$ and I can't see how the presence of sodium ions in solution would inhibit the second reaction (since that is the only difference between this solution and a solution of pure carbonic acid which does effervesce).

However very clearly this bubbling does not happen in real life, as anyone can easily verify for themselves. So what inhibits it then?

It's well known that if you put carbonic acid $\ce{H2CO3}$ into water it will dehydrate into carbon dioxide $\ce{CO2}$ and water $\ce{H2O}$. Indeed this is how modern fizzy drinks generate their fizz. Taking this as a given what I don't understand is why doesn't sodium bicarbonate dissolved in water not slowly give off $\ce{CO2}$ via the following pathway:

$$ \ce{HCO3- +H+ <=> H2CO3} $$ $$ \ce{H2CO3 -> H2O + CO2} $$

This would lead to the solution of sodium bicarbonate slowly converting itself into a solution of sodium hydroxide. The first part of the reaction is reversible and is something that at equilibrium will have a non-zero amount of $\ce{H2CO3}$. In fact given that carbonic acid is a weak acid there will be a lot of $\ce{H2CO3}$ present at equilibrium. I also can't see how the presence of sodium ions in solution would inhibit the second reaction (since that is the only difference between this solution and a solution of pure carbonic acid which does effervesce) so according to my understanding we should be seeing a fizz .

However very clearly this bubbling does not happen in real life, as anyone can easily verify for themselves. So what inhibits it then?

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Hadi Khan
Hadi Khan
  • 307
  • 1
  • 6

Why doesn't sodium bicarbonate dissolved in water spontaneously effervesce when carbonic acid does?

It's well known that if you put carbonic acid $\ce{H2CO3}$ into water it will dehydrate into carbon dioxide $\ce{CO2}$ and water $\ce{H2O}$. Indeed this is how modern fizzy drinks generate their fizz. Taking this as a given what I don't understand is why doesn't sodium bicarbonate dissolved in water not slowly give off $\ce{CO2}$ via the following pathway:

$$ \ce{HCO3- +H+ <=> H2CO3} $$ $$ \ce{H2CO3 -> H2O + CO2} $$

This would lead to the solution of sodium bicarbonate slowly converting itself into a solution of sodium hydroxide. The first part of the reaction is reversible and is something that at equilibrium will have a non-zero amount of $\ce{H2CO3}$ and I can't see how the presence of sodium ions in solution would inhibit the second reaction (since that is the only difference between this solution and a solution of pure carbonic acid which does effervesce).

However very clearly this bubbling does not happen in real life, as anyone can easily verify for themselves. So what inhibits it then?