# Write an equation to illustrate that a reaction is acidic.

• student34
In summary, P4O10 is a non-metallic oxide that reacts with water to produce H3O+ and a negative ion, making it an Arrhenius acid. The balanced equation for this reaction is P4O10(s) + 6H2O → 4H3PO4(aq). Phosphoric acid, which is produced in this reaction, is known for containing P and producing H3O+, making it a clear example of an acid.
student34

## Homework Statement

Write equations to illustrate whether P4O10(s) is an Arrhenius acid or a base.

## Homework Equations

P4O10(s) + H2O(l) will eventually have the H3O+ and a negative ion because it is a non-metallic oxide in water.

## The Attempt at a Solution

I can think of at least 10 different ways to come up with a H3O+ in the equation, but the answer has a specific answer which is,

P4O10(s) + 6H2O → 4H3PO4(aq)

I don't know why they have 6 H2O's.

I also don't know why they only use one of the 4 H3PO4(aq) for this equation,

H3PO4(aq) + H2O(l) → H3O+(aq) + H2PO4-(aq) .

I can't find anywhere in the chapter that explains how I would know this.

student34 said:
P4O10(s) + 6H2O → 4H3PO4(aq)
I don't know why they have 6 H2O's.
Try balancing the equation.
student34 said:
I also don't know why they only use one of the 4 H3PO4(aq) for this equation,
H3PO4(aq) + H2O(l) → H3O+(aq) + H2PO4-(aq) .
Did you wish to count individual molecules, or the stoichiometry?

student34
For the first question you might find it easier to write it as P2O5, write an obvious covalent structure for it with pentavalent P. See how H2O can be added to that in two stages.

For your second question, the means to answer it may be in another chapter - on buffers, pH calculations etc. All three protons of H3PO4 can diissociate. But only the first one is strongly acid. Actually what they write seems to me slightly arbitrary. From the first Ka of around 0.01 M it follows (easily ) that if you dissolved the pentoxide to around 0.01 M [P] about half of it would be in form H2PO4-; the greater the dilution the greater this fraction, while at higher concentrations the majority would be undissociated H3PO4 - e.g. at 1M about 90% is, and only 10% is H2PO4-, and very little other ionised forms.

Rereading maybe that was not your question. The scheme is not meant to represent 'only one' ot the four molecules - it represents any of them equally. That reaction is extremely fast and goes back and forth something like 108 times per second.

Last edited:
student34
Bystander said:
Try balancing the equation.

I understand that the equation is balanced. I just have no idea why they decided to end up with 4H3PO4(aq) instead of anything else. Of all of the possible molecules, how would I know to try using that molecule?

Did you wish to count individual molecules, or the stoichiometry?

This is half way through grade 11 chemistry (old student who is upgrading). I think stoichiometry is in the next chapter. So I think individual molecules would be expected for this question.

student34 said:
I just have no idea why they decided to end up with 4H3PO4(aq)

First - P4O10 is an acid anhydride and is known to react with water producing phosphoric acid. My bet is you were told that earlier.

Second - phosphoric acid is an obvious example of an acid containing P, and being able of producing H3O+.

student34

## What is an acidic reaction?

An acidic reaction is a chemical reaction that involves the production of hydrogen ions (H+) in a solution. This can be measured by a decrease in pH, which indicates an increase in the concentration of hydrogen ions.

## How do you write an equation to illustrate an acidic reaction?

An acidic reaction can be illustrated by writing a chemical equation that includes a substance that donates hydrogen ions in the reaction. This can be represented by a proton (H+) or hydronium ion (H3O+).

## What are the characteristics of an acidic reaction?

An acidic reaction typically involves the release of heat, production of hydrogen gas, or the formation of a salt and water. It also has a low pH (less than 7) and can be corrosive.

## What is an example of an acidic reaction?

An example of an acidic reaction is the reaction between hydrochloric acid (HCl) and sodium hydroxide (NaOH) to produce sodium chloride (NaCl) and water (H2O). The equation for this reaction is HCl + NaOH → NaCl + H2O.

## How do you know if a reaction is acidic?

A reaction is considered acidic if it produces a higher concentration of hydrogen ions (H+) in a solution. This can be measured by a decrease in pH, which indicates an increase in the acidity of the solution. Additionally, the presence of certain ions or molecules, such as hydrogen ions or hydronium ions, can also indicate an acidic reaction.

• Biology and Chemistry Homework Help
Replies
5
Views
1K
• Biology and Chemistry Homework Help
Replies
1
Views
2K
• Biology and Chemistry Homework Help
Replies
3
Views
3K
• Biology and Chemistry Homework Help
Replies
6
Views
3K
• Biology and Chemistry Homework Help
Replies
1
Views
1K
• Biology and Chemistry Homework Help
Replies
5
Views
7K
• Biology and Chemistry Homework Help
Replies
5
Views
3K
• Biology and Chemistry Homework Help
Replies
1
Views
2K
• Biology and Chemistry Homework Help
Replies
3
Views
2K
• Biology and Chemistry Homework Help
Replies
4
Views
1K