le chatelier's principle (1 Viewer)

[jnney]

Using LCP, account for the sharp acidic taste of soft drinks.

Soft drinks contain carbon dioxide dissolved in water.

To begin, CO2(g) is converted into CO2(aq) under pressure [as it is in a closed system]. CO2(g) <---> CO2(aq). By LCP, the equilibrium will favour the forwards reaction and shift right to the side with the fewer moles as to counteract the increased pressure. Hence, [CO2(aq)] increases.

In turn, the [CO2(aq)] also increases in the reaction between water. CO2(aq) + H2O(l) <---> H2CO3-(aq). By LCP, the equilibrium favours the forwards reaction and shifts to the right to decrease the increased [CO2(aq)]. This causes CO2(aq) to dissolve more readily, increasing the [H2CO2(aq)], producing the sharp acidic taste.

Is this correct? I'm kind of confused.

 

[Carrotsticks]

1. I think this question is poorly worded because there are other factors to take into account ie: temperature of the actual drink, is it still in the bottle? etc.

2. You should have some mention of Carbonic Acid , because it is this chemical which causes the sharp taste, and the funny tingly-feeling in your nose when you burp out after drinking soft drinks too quickly.

 

[rolpsy]

an increase in pressure will shift the equilibrium:
CO₂(g) ⇌ CO₂(aq)
to the right to reduce the gas pressure

this will push the equilibrium:
CO₂(aq) + H₂O(l) ⇌ H₂CO₃(aq)
to the right (i'm not entirely sure if this will drive the dissolution reaction to the right to minimise the change in concentration of CO₂(aq) – i'd assume it would)

the increase in carbonic acid shifts the equilibrium:
H₂CO₃(aq) ⇌ H⁺(aq) + HCO₃^-(aq)
to the right

also to some extent, the equilibrium:
HCO₃^-(aq) ⇌ H⁺(aq) + CO₃^2-(aq)
will occur

these acids (H₂CO₃(aq) and HCO₃^-(aq)) cause the sharp acidic taste.

 

[Carrotsticks]

these acids (H₂CO₃(aq) and HCO₃^-(aq)) cause the sharp acidic taste.

The Bicarbonate ion is amphoteric. Since it is involved in a reaction with , it acts as a base, not an acid.

 

[study-freak]

The Bicarbonate ion is amphoteric. Since it is involved in a reaction with , it acts as a base, not an acid.

If it reacts with a hydronium ion, it indeed then acts as a base, but that's not the only thing that's occurring. You thus cannot say that it's acting as a base only.


Plus, the most probable candidate for the cause of acidic taste is hydronium ions.
It's known that bicarbonate ions do not activate taste receptors.

 

[someth1ng]

I'm pretty sure HCO3-(aq) --> H+(aq) + CO3-(aq) as part of an equilibrium.
Then H2O(l) + H+ (aq) --> H3O+ (aq)

Since H3O+ is formed and is an acid, the sharp acidic taste is from the H3O+ ion.

 

[study-freak]

I'm pretty sure HCO3-(aq) --> H+(aq) + CO3-(aq) as part of an equilibrium.
Then H2O(l) + H+ (aq) --> H3O+ (aq)

Since H3O+ is formed and is an acid, the sharp acidic taste is from the H3O+ ion.

More like HCO3-(aq) +H2O(l) <-(eqilibrium)-> H3O+(aq) + CO3-(aq)
in one step.

The bolded part doesn't make any sense since if the reasoning is to make sense, H2CO3 is also an acid and so it should create the sharp acidic taste too.

The more correct reasoning would be that H3O+ is common to all aqueous acids.