Question

100. ml of 0.200M HCl is titrated with 0.250M NaOH.
1. What is the pH of the solution after 50.0ml of base has been added?
2.What is the pH of the solution at the equivalence point?

Answer 1

Concepts and reason

The concept used to solve this problem stoichiometry of balance reaction, which indicates the relationship between reactant and products of any chemical reaction.

Fundamentals

Acid-base neutralization reaction:

When an acid is reacted with base creating water or solvent and an ionic salt, the reaction is known as Acid-base neutralization reaction.

For example:

Molarity:

The number of moles of solute per liter of solution is known as molarity of the solution. It symbolized by . Molarity of any solution is a ratio of moles of solutes per liter of solution. It expressed by the following formula:

The titration of an acid with base:

The method of determine the quantity of an acid or a base by adding a calculated quantity of a base or an acid is called the titration of an acid with base.

Equivalent point:

Equivalent point is a point of acid-base titration where acid and base present in the stoichiometrically equivalent amount.

Indicator:

Indicator of acid-base titration is a compound that changes color according to changes of solution. In general the color of indicator of acid-base titration changes when the acidic solution becomes basic or basic solution becomes acidic.

End point:

End point of acid –base titration is a point at which the acidic solution becomes basic or basic solution becomes acidic means at this point the indicator changes its color. In general to determinate the end point we use an indicator in acid-base titration.

To calculate the number of moles uses the following expression:

[Part a]

The balance chemical reaction of strong acid and strong base is as follows:

Calculate the moles of acid and base as follows:

According to the balance reaction 1 mole reacts with 1 mole . Therefore

mole will recats with .

Moles of present in excess, which calculated as follows:

And Total volume of reaction = volume of + volume of

Now calculate the new molarity of as follows:

is an example of strong acid therefore the molarity of is equal to hydrogen ion concentration in the solution.

The is determined the nature of solution, which is defined as:

[Part a]

Part a

Ans: Part a

Thus, the the pH of the solution after 50.0ml of base has been added is 1.30.