Molarity of Unknown and sodium hydroxide.

[imaciel]

This is the question:

Your friend gives you an unlabeled bottle that contains either hydrochloric, sulfuric or phosphoric acid. The concentration of the unknown acid is 0.2128 M. A titration of 21.00 mL of the acid with a 0.2723 M sodium hydroxide solution required 32.83 mL of sodium hydroxide. Which of the three acids is in the bottle?

A. sulfuric acid
B. hydrochloric acid
C. phosphoric acid

Steps:
I solved for the molar mass of 3 choices, but I don't know how to get the molar mass from the problem. I can get # of moles in the solution but what about gram?

molar mass= gram/moles...

tnx

 

[chemisttree]

Your titration will tell you how many moles of H+ are present. The result should be an integer multiple of 0.2128.

Enough of a hint?

 

[Blueshift5]

I would approach this problem by first understanding the concept of molarity and titration. Molarity is a measure of concentration, defined as the number of moles of a solute per liter of solution. Titration is a technique used to determine the concentration of an unknown solution by reacting it with a known solution of known concentration.

In this scenario, we are given the molarity of the unknown acid (0.2128 M) and the volume of the titrant (sodium hydroxide) used in the titration (32.83 mL). From this information, we can calculate the number of moles of sodium hydroxide used in the titration:

moles of sodium hydroxide = molarity x volume (in liters)
= 0.2723 M x 0.03283 L
= 0.00894 moles

Since the titration is a neutralization reaction, we can assume that the number of moles of sodium hydroxide used is equal to the number of moles of the unknown acid present in the solution. Therefore, we can use this information to determine the number of moles of the unknown acid:

moles of unknown acid = moles of sodium hydroxide
= 0.00894 moles

Now, we need to use the given volume of the unknown acid (21.00 mL) to calculate its molarity:

molarity = moles of unknown acid / volume (in liters)
= 0.00894 moles / 0.02100 L
= 0.4257 M

Comparing this molarity to the given options of sulfuric acid (0.2128 M), hydrochloric acid (0.2128 M), and phosphoric acid (0.2128 M), we can see that the molarity of the unknown acid (0.4257 M) is twice the molarity of sulfuric and hydrochloric acid, but the same as the molarity of phosphoric acid. This suggests that the unknown acid is most likely phosphoric acid.

To confirm this, we can also calculate the molar mass of each acid and compare it to the given information. The molar mass of phosphoric acid is 98.0 g/mol, while the molar mass of sulfuric acid is 98.1 g/mol and the molar mass of hydrochloric acid is 36.5 g/mol. From