# Find the molecular mass of acid in acid base neutralization

• Chemistry
• jessica.so
In summary: I was given a 100.00 mL volumetric flask with 1.5000 g of H2A inside. From this, I took a 25.00 mL aliquot and titrated it with 40.00 mL of NaOH to find the molarity of the H2A. However, I am not sure if my calculations are correct or if I missed something in the process. In summary, a 100.00 mL volumetric flask contained 1.5000 g of diprotic weak acid H2A. From this, a 25.00 mL aliquot was titrated with 40.00 mL of monoprotic strong base NaOH (0.08000
jessica.so

## Homework Statement

1.5000 g of diprotic weak acid H2A was dissolved in 100.00 mL volumetric flask.
25.00 mL aliqouts of this solution was titrated with a monoprotic strong base NaOH (0.08000 M). The titre volume of NaOH was 40.00 mL. Calculate the molecular weight of H2A.

N/A

## The Attempt at a Solution

1 mole of H2A contains 2 moles of H+
1 mole of NaOH contains 1 mole of OH-

2CaVa = CbVb
2 (Ca)(0.02500 L) = (0.0800 M)(0.04000L)
Ca = 0.0640 M

#moles of H2A = CaVa
= (0.0640 M)(0.10000 L)
= 0.00640 mol

molecular mass of H2A = mass/# moles
= 1.5000 g / 0.00640 mol
= 234.375 g/mol

My answer is 234.375 but something seems odd about it. Can anyone tell me if I missed something or did something wrong? Thanks!

Last edited:
jessica.so said:
2CaVa = CbVb

Question is - is that 2 in the correct place?

Last edited by a moderator:
I've always been taught that the exponent in CaVa = CbVb equations is the number of moles of H+ ions or OH- ions which is why I put the 2 infront of the CaVa.

Another time I attempted this question but I balanced the neutralization first.
H2A + 2 NaOH --> 2 H2O + Na2A

CaVa = 2 CbVb
(Ca)(0.02500 L) = 2(0.0800 M)(0.04000L)
Ca = 0.256 M

#moles of H2A = CaVa
= (0.256 M)(0.10000 L)
= 0.0256 mol

molecular mass of H2A = mass/# moles
= 1.5000 g / 0.0256 mol
= 58.59 g/mol

This answer seemed wrong too somehow. One of the questions that came up was that the acid we are neutralizing is a weak acid. 25mL of this weak acid was neutralized by 40mL of strong base. Shouldn't a weak acid take less base to neutralize?

Last edited:
Exponent? I guess you mean stoichiometric coefficient. But you were right the first time, somehow I got it reversed.

Now, the problem is - 0.00640 moles - is it whole 1.5 g sample?

Strength of the acid has nothing to do with amount of base that it needs to be neutralized. It is all in stoichiometry.

So sorry! Yes, I did mean the coefficient.

So...I'm using the first attempt...

2CaVa = CbVb
2(Ca)(0.02500 L) = (0.0800 M)(0.04000L)
Ca = 0.0640 M

#moles of H2A = CaVa
= (0.0640 M)(0.10000 L)
= 0.00640 mol

molecular mass of H2A = mass/# moles
= 1.5000 g / 0.00640 mol
= 234.375 g/mol

So I found the molarity of the H2A that was neutralized. Because a 25.00 mL sample was taken from the 100.00 mL solution, the molarity stays the same. 1.5000 g made the 100.00 mL solution of H2A so I think the 0.00640 mol is the whole 1.5 g sample.

have you titrated 100 mL aliquot?

No, I have not titrated 100mL

## 1. What is acid base neutralization?

Acid base neutralization is a chemical reaction between an acid and a base that results in the formation of a salt and water. It is a common reaction used in many industries and also occurs naturally in the human body.

## 2. What is the molecular mass of acid in acid base neutralization?

The molecular mass of acid in acid base neutralization depends on the specific acid being used. It is calculated by adding the atomic masses of all the elements present in the molecule. For example, the molecular mass of hydrochloric acid (HCl) is 36.5 g/mol, while the molecular mass of sulfuric acid (H2SO4) is 98 g/mol.

## 3. How is the molecular mass of acid determined in acid base neutralization?

The molecular mass of acid can be determined by using a mass spectrometer, which measures the mass-to-charge ratio of ions in a sample. The molecular mass can also be calculated using the chemical formula of the acid and the atomic masses of its elements.

## 4. What is the significance of finding the molecular mass of acid in acid base neutralization?

Knowing the molecular mass of acid is important for accurately measuring and predicting the amount of acid needed in a neutralization reaction. It also helps in understanding the properties and behavior of the acid in the reaction.

## 5. Can the molecular mass of acid affect the outcome of acid base neutralization?

Yes, the molecular mass of acid can affect the outcome of acid base neutralization. The amount of acid needed to neutralize a base is dependent on its molecular mass, as well as the concentration and volume of the acid. Therefore, a higher molecular mass acid may require more moles to neutralize a base compared to a lower molecular mass acid.

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