# What would be the proper way to solve a titration problem?

• Eclair_de_XII
In summary, a 4.36-g sample of an unknown alkali metal hydroxide was titrated with 2.50 M HCl solution, reaching the equivalence point after 17.0 mL of HCl was added. Using the equation for molarity, the number of moles of HCl was found to be 0.0425 mol. By assuming that the moles of HCl equal the moles of hydroxide, the molar mass of the unknown hydroxide was calculated to be 103 g/mol. Based on this, it was determined that the unknown alkali metal was most likely rubidium (Rb).
Eclair_de_XII

## Homework Statement

"A 4.36-g sample of an unknown alkali metal hydroxide is dissolved in 100.0 mL of water. An acid-base indicator is added and the resulting solution is titrated with 2.50 M HCl (aq) solution. The indicator changes colour signaling that the equivalence point has been reached after 17.0 mL of the hydrochloric acid solution has been added."

a) What is the molar mass of the metal hydroxide?
b) What is the identity of the alkali metal cation: Li+, Na+, K+, Rb+, or Cs+?

## Homework Equations

Molarity = moles solute / volume of solution in liters

## The Attempt at a Solution

First, I found the moles for HCl:
moles solute / volume of solution in liters = molarity
moles solute = molarity (volume of solution in liters)
0.0425 mol HCl = 2.5(0.017)
Now I guessed that 0.0425 mol of HCl is supposed to react with 0.425 (?)OH to produce H2O and (?)Cl. Then I tried to find the moles of all the possible alkali metal hydroxides by adding the molar mass of hydrogen and oxygen, then adding them to the different alkali metals. Then I took my given mass of 4.36 g and divided it by each of those molar masses. If the result was not 0.0425, then I eliminated it as a solution. This is my final result:
4.36/102.47514 = 0.0425 mol RbOH, where 102.47514 = 1.00794 + 15.9994 + 85.4678. I then concluded that the alkali metal was rubidium, seeing how the numbers matched up.
However, I am completely sure this is not the correct way to do this problem. Could someone tell me how they would do this titration problem?

Eclair_de_XII said:

## Homework Statement

"A 4.36-g sample of an unknown alkali metal hydroxide is dissolved in 100.0 mL of water. An acid-base indicator is added and the resulting solution is titrated with 2.50 M HCl (aq) solution. The indicator changes colour signaling that the equivalence point has been reached after 17.0 mL of the hydrochloric acid solution has been added."

a) What is the molar mass of the metal hydroxide?
b) What is the identity of the alkali metal cation: Li+, Na+, K+, Rb+, or Cs+?

## Homework Equations

Molarity = moles solute / volume of solution in liters

## The Attempt at a Solution

First, I found the moles for HCl:
moles solute / volume of solution in liters = molarity
moles solute = molarity (volume of solution in liters)
0.0425 mol HCl = 2.5(0.017)
Now I guessed that 0.0425 mol of HCl is supposed to react with 0.425 (?)OH to produce H2O and (?)Cl. Then I tried to find the moles of all the possible alkali metal hydroxides by adding the molar mass of hydrogen and oxygen, then adding them to the different alkali metals. Then I took my given mass of 4.36 g and divided it by each of those molar masses. If the result was not 0.0425, then I eliminated it as a solution. This is my final result:
4.36/102.47514 = 0.0425 mol RbOH, where 102.47514 = 1.00794 + 15.9994 + 85.4678. I then concluded that the alkali metal was rubidium, seeing how the numbers matched up.
However, I am completely sure this is not the correct way to do this problem. Could someone tell me how they would do this titration problem?

I think your reasoning looks fine. What I would say is that you know that the moles of hydroxide equals moles of acid. (All alkali metals have +1 charge as ions). You also know grams of alkali hydroxide. Molecular weight is grams divided by moles. So the molecular weight is 4.36 g/ 0.0425 mol = 103 g/mol. Since RbOH is closest to this, the sample is most likely RbOH.

## 1. What is a titration problem?

A titration problem is a type of analytical chemistry problem where the concentration of an unknown substance is determined by reacting it with a known substance. This is typically done by gradually adding the known substance (called the titrant) to the unknown substance until a chemical reaction reaches a specific endpoint.

## 2. What is the proper equipment needed for a titration problem?

The proper equipment for a titration problem includes a burette, a pipette, a flask, and a pH indicator. The burette is used to measure and dispense the titrant, while the pipette is used to measure the volume of the unknown substance. The flask is used to hold the unknown substance, and the pH indicator is used to determine the endpoint of the titration reaction.

## 3. What is the first step in solving a titration problem?

The first step in solving a titration problem is to accurately measure the volume of the unknown substance using a pipette. This volume will be used to calculate the concentration of the unknown substance.

## 4. How do you determine the endpoint of a titration reaction?

The endpoint of a titration reaction is determined by using a pH indicator. This indicator changes color when the reaction reaches a specific pH, indicating that the reaction is complete. Common indicators used in titrations include phenolphthalein, bromothymol blue, and methyl orange.

## 5. What calculations are involved in solving a titration problem?

In order to solve a titration problem, you will need to use the volume of the unknown substance, the concentration of the titrant, and the volume of the titrant used at the endpoint to calculate the concentration of the unknown substance. This can be done using the formula M1V1 = M2V2, where M1 is the concentration of the unknown substance, V1 is the volume of the unknown substance, M2 is the concentration of the titrant, and V2 is the volume of the titrant used at the endpoint.

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