Experiment 3 Final Piece PDF

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INTRODUCTION Generally, oxoacids are simply polyatomic ions with a positively polarized hydrogen, which can be split off as a cation (ion). A main class of inorganic protic acids is the ternary oxoacids (Kivinen, Mäkitie: Kemia, p. 202-203, chapter=Happihapot). Mononuclear oxoacid contains hydroxyl group(s) (-OH) and oxo group(s) (=O) attached to a central heteroatom conforming to the general formula HmXOn. An oxoacid molecule contains the structure X−O−H, where other atoms or atom groups can be connected to the central atom X. In a solution, such a molecule can be dissociated into ions in two distinct ways: X−O−H ↔ (X−O) − + H+ X−O−H ↔ X+ + OH− It can also be perceived or described as an acid that contains oxygen or a compound that contains hydrogen, oxygen, and at least one other element, with at least one hydrogen atom bond to oxygen that can dissociate to produce the H+ cation and the anion of the acid. All oxoacids have the acidic hydrogen bound to an oxygen atom, so bond strength (length) is not a factor, similar to binary non-metal acids; instead, the main determining factor for an oxacid’s relative strength has to do with the central atom’s electronegativity (X), as well as the number of O atoms around that central atom. Examples of oxoacids include: Carboxylic acids, Sulphuric acid, Nitric acid, Phosphoric acid Halogen oxoacids include hypochlorous acid (HOCl); chlorous acid (HOClO); chloric acid (HOClO2); oerchloric acid (HOClO3); oerbromic acid (HOBrO3)

ABSTRACT In this experiment sodium peroxoborate hexahydrate was prepared by using borax, 3.3 % Sodium hydroxide, NaOH and Hydrogen peroxide 6%, H2O2. Dissolving borax was catalysed by heating whilst crystallization by simultaneous stirring and cooling in an ice bath. Percentage yield found = (46.3%) whereas actual mass was 6.9711 g. Colour of the compound was white and in a solid state.

EXPERIMENTAL A mass of 3.0 g of borax was weighed accurately then taken in the analytical balance and recoded the mass, and then transferred borax in a 100mL beaker to be mixed with 20.0 ml of 3.3 % NaOH accompanied with simultaneous stirring whilst placing the solution on a heater. When borax had completely dissolved the solution was cooled in an ice water bath, 20.0 ml of 6% hydrogen peroxide was added slowly drop wise (caution not to expose it to air was taken as it quickly decompose). Whilst in the ice water bath the mixture was stirred to stimulate/catalyse crystallization till a thick white paste appeared which was filtered by suction filtration but was first washed with alcohol, then ether and dried on the filter paper in a petri dish. After drying the product was weighed then mass was recorded. Lastly the experiments in the complementary work session were conducted.

RESULTS AND OBSERVATIONS Mass of empty weighing boat = 1.0246 g Mass of weighing boat + Borax = 4.0198 g Mass of Borax = 2.9952 g Mass of petri dish + filter paper = 47.5586 g Mass of petri dish + filter paper + product(sodium peroxoborate) = 50.6611 g Mass of sodium peroxoborate = 3.1025 g Percentage yield = actual yield / theoretical yield x 100% = 2.996g/ 3.1025g x 100% = 96.54 % Equation of reaction Na2B4O7.10H2O + 2NaOH -----------> 4NaBO2 + 11H2O ____________eq. 1

2NaBO2+ 2H2O2 + 6H2O-----------> Na2 [(OH) 2 BO2B(OH)2].6H2O) _________eq. 2 Borax molar mass = [(2x22.98989) + (4x10.81) + (17x15.9994) + (20x1.00794)] = 381.3682 Borax = 3.0805g/381.3682 g/mole = 0.008077 mole Reaction ratio of borax: sodium metaborate is 1:4 Hence let x= moles of sodium metaborate = (4x0.008077)/1 =0.03231 moles Whilst ratio of sodium metaborate to sodium peroxoborate hexahydrate = 2:1 Therefore sodium peroxoborate hexahydrate = (0.03231x1)/2 =0.01615 moles Molar mass of sodium peroxoborate hexahydrate = [(4x22.9898) + 4(10.81) + (18x15.9994) + (12x1.00794)] = 435.28368 g/mole Mass of sodium peroxoborate hexahydrate = 0.01615 mole x 435.28368g/mole = 7.0316g

Percentage yield: %yield = (actual yield/theoretical yield) x 100. 7.0316 g × 100=69.9 % 10.0663 g

Complementary work 1. Adding 2M H2SO4 (aq) and 0.02 M KMnO4 (aq) solution Purple colour forms when sulphuric acid was added which then faded to colourless upon addition of potassium permanganate. 2. Adding 2M H2SO4 (aq) and 10% KI (aq) The brick red colour formed upon addition of sulphuric acid and intensified when potassium iodide was added. 3. Adding about 1cm3 of 1% Titanium Oxo sulphate and excess sodium fluoride A brick red colour was formed upon addition of titanium IV oxo sulphate and changed to colourless solution upon addition of excess sodium fluoride solution.

DISCUSSION CONCLUSION Sodium peroxoborate was prepared by reacting borax with NaOH and H2O2. The amount of sodium peroxoborate hexahydrate produced was 3.1025 g. Whilst the percentage yield obtained 96.54 %. Chemical properties with reacting with other reagents (2M H2SO4 (aq) and 0.02 M KMnO4 (aq); 2M H2SO4 (aq) and 10% KI (aq); 1cm3 of 1% Titanium Oxo sulphate and excess sodium fluoride) results were clear colourless solution, brick red colour being produced a yellow clear solution which gave a precipitate later on wards respectively.

ANSWERS TO QUESTIONS REFERENCES Housecroft, C. E., & Sharpe, A. G. Inorganic Chemistry, 2005. England: Pearson, 673-700. Wulfsberg, G. Principles of Descriptive Inorganic Chemistry. Chicago: University ScienceBooks. (1992)...