Superior Essay Writers | Acid-Base Titration Curves

Acid-Base Titration Curves

In this experiment you will use a volumetric titration to determine the titration curve for a weak acid. You will determine the equivalence point for the acid and calculate the molar concentration of the acid solution.

Materials
Chemicals
Ammonia solution- NH3 (1M) (SDS)
Vinegar

Equipment from Home
Distilled water
Cell phone camera
Clear tape to secure syringe
Microsoft Excel or another spreadsheet program

      Equipment from Kit
Goggles & gloves
50 mL & 10 mL graduated cylinders
250 mL & 150 mL beakers
pH meter & buffer solutions
syringe and stopcock
funnel
pipettes

Introduction

Acid-Base titration curves are graphs that show the successive pH values that occur during the titration of a base with an acid or an acid with a base. The general purpose of a titration is to determine the amount of a particular substance in a sample. An acid-base titration curve can be used to find the equivalence point, which is the point where equal stoichiometric moles of been added. The volume of base added (titrant) at the equivalence point can be used to find the moles of acid in an unknown solution.

An Acid-Base titration curve will vary depending on the strength of the acids and bases. When a strong acid is titrated with a strong base, the curve will rise sharply and have an equivalence point at pH = 7. If a weak acid is titrated with a strong base or a weak base is titrated with a strong acid the titration curve is unique because one of the ions in the salt formed will often hydrolyze in water. For a weak acid, the equivalence point will be at a pH higher than 7. For a weak base it will be lower than 7.

Volumetric Titration

A titration is a process used to determine the volume of a standard solution that is needed to react with a given amount of another substance. In this experiment, your goal is to determine the molar concentration of an acid solution by conducting titrations with a base of known concentration. You will be testing a weak acid found in vinegar, acetic acid (HC2H3O2). You will use ammonia (NH3) solution as your base of known concentration. The reaction equation is shown below in net ionic form.
HC2H3O2(aq) + NH3 (aq) ↔ NH4+ (aq) + C2H3O2– (aq)

Notice that a double arrow is used since this is a reversible reaction, or equilibrium, since it is a weak acid. A weak acid is one that doesn’t completely dissociate in solution.
In this experiment, you will use a pH meter to monitor pH as you titrate. The region of most rapid pH change will then be used to determine the equivalence point. The volume of NH3 titrant used at the equivalence point will be used to determine the molarity of the acid solution.

Calculating acid concentration

Molarity is defined as the moles of solute divided by the liters of solution. Therefore, if you know the molarity of NH3 and the volume used, you can determine the total moles.

First, convert the volume of NH3 added to liters (L). Next calculate the moles of NH3 using the volume and the molarity of the NH3, found on the bottle.

moles NH3 at equiv. = vol. (in L) NH3 at equiv. x [molarity of NH3]

OR moles NH3 = V x M

Next, determine the moles of acid in the vinegar at equivalence by using the balanced chemical reaction and the mole ratio:

           1 mole HC2H3O2 = 1 mole NH3

Finally, calculate the molarity (M) of the acetic acid in the vinegar sample

      Molarity of 〖HC〗_2 H_3 O_2 = (moles 〖HC〗_2 H_3 O_2)/(volume(in L)  of〖HC〗_2 H_3 O_2  )

Procedure

Wear goggles and gloves for this experiment.
Obtain the buret (looks like a plastic syringe) from your kit. Remove the plunger from the syringe; it is not needed here.
Screw the stopcock onto the threaded tip of the syringe. You can rotate the valve on the stopcock to a position that is either closed (perpendicular to the syringe), open (parallel to the syringe), or anywhere in between. 
Rinse the syringe with distilled water. Check that the stopcock at the bottom is working properly and is not leaking.

Using a very long (> 6 inches) piece of clear tape, secure the syringe to the wall or another sturdy support. Your set

Sample Solution

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