The Ka and Molar Mass of a Monoprotic Weak Acid Essay

The purpose of this semester long experiment was to determine an unknown organic acid. An organic acid is an organic compound with acidic properties. A base reacts with acids to form salts. Titrations are used to determine the concentration of unknown substances. The purpose of the KHP experiment was to determine the molarity of NaOH. HCl titrations are mainly to check technique and used to verify the molarity of NaOH solution. The hypothesis is that this acid is C4H3OCOOH.

To start out this study the difference between acids and bases has to be identified. Acids have very low pHs and have a high concentration of hydronium ions, while bases have a high pH and have a high concentration of hydroxide ions. The difference between strong bases and acids, and weak bases and acids is the amount of dissociation. Strong bases and acids dissociate a large amount and let go of their ions in solution, while weak bases and acids may only let go of some of their ions. This is important because if the unknown solutions aren’t strong acids or bases then using their ions to calculate the pH of the solutions will give false results (Diffen 2012).

Acids are substances that donate hydrogen ions and bases are substances that accept hydrogen ions. Acids and bases react with each other by transferring hydrogen ions. One way to distinguish an acid is by its equivalent mass, which is the number of grams of the acid needed to transfer one mole of hydrogen ion to a base. For a monoprotic acid, which only transfers one hydrogen ion, its equivalent mass equals its molar mass. For a diprotic acid, which transfers two hydrogen ions, its equivalent mass equals half its molar mass. The equivalent mass of a base is simply the number of grams required to accept one mole of hydrogen

Partially weak acids don’t fully react to completion to release all their protons, and so do not react fully, and do not change the pH dramatically. This depends on buffering capacity and concentrations.

Ka is the acid dissociation constant and [HA] is the concentration of the weak acid . Strong acids usually completely dissociate and has a Ka value greater than 1. Weak acids don’t dissociate completely and have a Ka value much smaller than 1. pKa values are often used for weak acids due to being able to work with whole numbers

Identifying this organic acid was an extensive task that involved several different experiments. Firstly, the melting point had to be determined. Since melting point can be determined to an almost exact degree, finding a close melting point of the specific unknown can accurately point to the identification of the acid. In this case the best melting point

One milliliter of 6.00-M phosphoric acid was placed into a 125-mL Erlenmeyer flask using a volumetric pipette. Using a slightly larger pipette, six milliliters of 3.00-M sodium hydroxide was transferred into a 50-mL beaker. Then a disposable pipette was used to slowly mix the sodium hydroxide into the phosphoric acid while the solution was swirled around. Then both the beaker and flask were rinsed with 2-mL of deionized water and set aside. A clean and dry evaporating dish was weighed with watch glass on a scale. Then the solution was poured into the dish and the watch glass was placed on top. The solution was then heated with a Bunsen burner to allow for the water to boil off to reveal a dry white solid. After the dish cooled to room temperature it was once again weighed and the new mass was recorded.

The purpose of this lab was to become familiar with the three different balances and two different methods used to find the weight and mass of chemicals and compounds in the ChemLab program. The lab was performed by using three different types of balances, and the direct weighing and weighing by difference methods.

For lab eight, the molarity of the NaOH solution is 0.07823 M. For lab nine, the molarity of the NaOH solution is 0.4224 M. The molarity of the NaOH solution for both lab eight and nine was not accurate because the solution did not turn the color to pink. Some source of error in this lab is oxalic acid is not completely moved from the plastic lab tray to the beaker. There is a small amount of substance left in the plastic lab tray that cause the mass of the beaker with NaOH solution to have less mass than I measured previously. Another source of error is not all the base was delivered from the burette to the beaker with oxalic acid. Some base remained on the side of burette instead of fully going into the beaker. This leftover base would change

“The pH of the solution formed from the reaction of a weak acid with a weak base depends on the relative strengths of the reactants. For example, if the acid HClO has a Ka of 3.4 x 10-8 and the base NH3 has a Kb = 1.6 x 10-5, then the aqueous solution of HClO and NH3will be basic because the Ka of HClO is less than the Ka of NH3.” (Helmenstine, 2004)

Weak electrolytes only partially break into ions in water. Weak electrolytes include weak acids, weak bases, and a variety of other compounds. Most compounds that contain nitrogen are weak electrolytes.

pH means potential hydrogen. pH is a measure of H3O+. Hydrogen ions are responsible for determining acid and base since an acid is identified if it gives off a hydrogen, while a base is identified if it receives a hydrogen ion from an acid. The pH scale measures the acidity or alkalinity of water soluble substances. A pH value is can range from 1 to 14, since 7 is in the middle it is known as the (neutral) point. Values below 7 are acidic which increases as the number decreases, 1 would be the most acidic. One theory is the Arrhenius which demonstrates that the acid produces hydrogen ions in a water solution, and that the base hydroxide ions in a water solution. The second theory is The Bronsted theory which shows that the acid is the proton

To keep this a fair test I have made sure that the acid used is the

An acid is a substance that produces hydrogen ions, H+ or hydrodium ionsH3O+ in solution. There are three “kinds of acids”: Arrhenius, BrØnsted-Lowry, and Lewis Acid. An Arrhenius acid is a substance the increases the concentration of hydrogen ion, H+ or hydronium ions H3O+when dissolved in water. You must have water. A BrØnsted-Lowry acid is any substance that donates a hydrogen ion, H+ to another substance. A

50 mL of an unknown amino acid was given and its initial pH was measured. Next, the amino acid was titrated with .1 N NaOH in increments of .5 mL. With every .5 mL of NaOH added to the amino acid solution pH of the mixture was taken and a titration curve was created. Henderson-Hasselbalch equation was used to determine the pKa’s of the unknown amino acids. pKa1 was determined to be 2.39. Equivalence also known as the pI point occured at a pI of 7.94.