Preparation and Properties of Boric Acid
Preparation and properties of boric acid
Result
The mass of borax, g | 10.0734 | The mass of watch glass, g | 36.2842 | The mass of watch glass with product, g | 39.9803 | The mass of product, borix acid, g | 3.6961 |
Test | Result | Boric acid is dissolved in water and methyl red indicator is added. | Pink solution is observed | Mannitol is dissolved in water and methyl red indicator is added. | Pink solution is observed | Both solution is added together | The colour of solution remain unchanged | A little methanol and concentrated sulphuric acid is added to boric acid, the solution is heated and the vapour evolved is ignited | The vapour evolved gave green flame when tested with ignited wooden splinter. |
Calculation
Relative molecular mass of borax = 381.24 gmol-1
Number of moles of borax = massRMM = 10.0734381.24 = 0.02642 mol
Na2B4O7.10H2O +2HCl → 2NaCl + 4H3BO3 + 5H2O
1moles of borax reacts with hydrochloric acid to produce 4 mole of boric acid with some side products.
Number of moles of boric acid = number of moles of borax X 4 = 0.02642 X 4 = 0.1057 mol
Theoretical mass = number of moles X relative molecular mass = 0.1057 X 61.81 = 6.533g
Experimental yield = 3.6961g
Percentage yield = 3.69616.533 X 100% = 56.56%
Discussion
Methyl red is a pH indicator that detected the pH changes. The pH changing range is around 4 to 6. Methyl red shows red at pH 4 whereas it shows yellow at pH 6.
Methyl red is added to aqueous solution of mannitol showing pink colour solution. This indicated that mannitol is acidic in aqueous solution. Boric acid is the Lewis acid that interacts with water molecules to produce hydrogen ions and tetrahydroxyborate ion in the solution. Therefore, a pink solution is shown after adding methyl red.
After adding boric acid to the mannitol, the solution remain pink. Boric acid react with mannitol give complex which is acidic.
Little methanol and concentrated sulphuric
Result
The mass of borax, g | 10.0734 | The mass of watch glass, g | 36.2842 | The mass of watch glass with product, g | 39.9803 | The mass of product, borix acid, g | 3.6961 |
Test | Result | Boric acid is dissolved in water and methyl red indicator is added. | Pink solution is observed | Mannitol is dissolved in water and methyl red indicator is added. | Pink solution is observed | Both solution is added together | The colour of solution remain unchanged | A little methanol and concentrated sulphuric acid is added to boric acid, the solution is heated and the vapour evolved is ignited | The vapour evolved gave green flame when tested with ignited wooden splinter. |
Calculation
Relative molecular mass of borax = 381.24 gmol-1
Number of moles of borax = massRMM = 10.0734381.24 = 0.02642 mol
Na2B4O7.10H2O +2HCl → 2NaCl + 4H3BO3 + 5H2O
1moles of borax reacts with hydrochloric acid to produce 4 mole of boric acid with some side products.
Number of moles of boric acid = number of moles of borax X 4 = 0.02642 X 4 = 0.1057 mol
Theoretical mass = number of moles X relative molecular mass = 0.1057 X 61.81 = 6.533g
Experimental yield = 3.6961g
Percentage yield = 3.69616.533 X 100% = 56.56%
Discussion
Methyl red is a pH indicator that detected the pH changes. The pH changing range is around 4 to 6. Methyl red shows red at pH 4 whereas it shows yellow at pH 6.
Methyl red is added to aqueous solution of mannitol showing pink colour solution. This indicated that mannitol is acidic in aqueous solution. Boric acid is the Lewis acid that interacts with water molecules to produce hydrogen ions and tetrahydroxyborate ion in the solution. Therefore, a pink solution is shown after adding methyl red.
After adding boric acid to the mannitol, the solution remain pink. Boric acid react with mannitol give complex which is acidic.
Little methanol and concentrated sulphuric