Assay of Borax

Molecular Formula: Na₂B₄O₇⋅10H₂O 

Molecular Weight: 381.4 

Assay: Weigh accurately about 3 g of borax dissolved in 75 mL of water and titrate with 0.5N hydrochloric acid using methyl red as an indicator. The endpoint will be yellow to red. 

Reaction: 

Na₂B₄O₇ ⟷ 2Na⁺ + B₄O₇^-2 

B₄O₇^-2 + 7H₂O ⟷ 4H₃BO₃  

2HCl + 2OH⁻ ⟷ 2H₂O + 2Cl⁻ 

Na₂B₄O₇⋅10H₂O ⟷ 2NaCl + 4H₃BO₃ + 5H₂O 

Factor Calculation: 

2 Moles of HCl ≅ 1 Mole of Borax 

2000 mL of 1M HCl ≅ 381.4 g of Na₂B₄O₇⋅10H₂O

1 mL of 0.5 M HCl ≅ 0.09535 g of Na₂B₄O₇⋅10H₂O

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