Determine Unknown Element in Monoprotic Acid

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To determine unknown element of acid, just titrate it against a solution of bases of known concentration. Chemical characteristic of dragon fruit and red cabbage would be explored in the experiment and colour range of dragon fruit juice and red cabbage juice at different pH would be determined. The objective of the experiments also was to know the characteristic of acidic gas and alkaline gas.

Acids are compounds which donate H+. Meanwhile, bases are simply defined as compounds that produce OH- ions. Neutralization of acids occur when they react with bases to form salt and water molecule at pH 7. Strong acids and bases dissociate completely in water but weak acids and bases dissociate slightly. When the color of an indicator is used to test for neutralization, the final pH may differ from pH 7 depending on the indicator used. It will also differ from pH 7 in reaction between strong acids and weak bases, weak acid and strong bases. This is because the salt formed will have acidic or basic properties respectively.

Titration was used to study acid-base neutralization reaction quantitatively. It is a volumetric technique used to determine the concentrations of solutions. A titration involves the addition of a titrant to solution of unknown concentration until it reaches an equivalence point. The equivalence point was the point at which the acid was completely reacted with or neutralized by the base. The point was signaled by a changing of color of an acid-base indicator that had been added to the acid solution.

An acid-base indicator is often a complex organic dye that undergoes the color change when the pHchanges over specific values. They can be used in the titration of a wide range of weak acids and bases. Many plant pigments and other natural products are good indicator

Determine Unknown Element in Monoprotic Acid



0.100M NaOH solution

0.26g of an unknown acid with the formula, HA

Few drops of phenolphthalein

10mL of water


Conical Flask


Weighing bottle


Weigh accurately about 0.26g of unknown acid and add 10mL of water to dissolve it completely along with a few drops of phenolphthalein indicator. Then, transfer it to conical flask.

Place the 0.100M NaOH solution in the burette and record the first reading.

Titrate unknown acid solution against the NaOH solution until the first permanent pink colour is obtained.

Record your reading in the table.


_Table 1: Burette readings_

Final reading (cm3)


Initial reading (cm3)


Volume of NaOH (cm3)



HA(s) + OH- (aq)→ A- (aq) + H2O(l)

Mole of NaOH = (0.0565 L x0.100M) = 0.00565 mol Number of moles of NaOH equal to number of moles of HA. Thus, initial of HA is 0.00565mol.

Molar Mass of HA= 0.26 / 0.00565 = 46.02 g.

The element which has molar mass of 46.02 g/mol is HCOOH. So, HA is HCOOH, formic acid is monoprotic acid that contains one ionizable hydrogen atom per formula unit.


NaOH (aq) + HCOOH (s) → H2O(l) + NaCOOH(aq)

The reaction between sodium hydroxide and formic is known as neutralization.

Acid + Base/Alkaline → Salt + Water

The products of the reaction are salt (sour salt) and water. During the process, hydrogen ions (H+) from formic and hydroxide ions (OH-) from sodium hydroxide react together to form water.

Formic acid has 1.22 g/mL desity which appear to be colourless normally. The actual molar mass of formic acid is 46.03 g mol-1. It has the lowest molecular weight and is the simplest of the carboxylic acids. Functionally, it is both an acid and an aldehyde. Like other acids, it reacts with most alcohols to form esters and decomposes when heated. However, it also has the same properties as other aldehydes, it is easily oxidized. Formic acid can be made by the oxidation of formaldehyde. It is prepared commercially by heating carbon monoxide and...
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