Dr Anima Upadhyay viva voce questions on Estimation of CaO in Cement by rapid EDTA Method

Summary

Key Points

• The experiment involves estimating calcium oxide in cement using a rapid EDTA method, which is considered rapid because complex formation is instantaneous. 0:37
• EDTA stands for ethylene diamine tetra acetic acid, and a standard solution of its disodium salt is used because it is soluble in water, unlike EDTA itself. 1:05
• The titration procedure involves preparing a standard EDTA solution, taking a cement sample, adding reagents like KCN, diethylamine, and sodium hydroxide, followed by a few drops of Pattinson's indicator. 1:56
• Diethylamine is added to adjust the pH to around 12.5, and sodium hydroxide is used to mask magnesium ions by forming magnesium hydroxide, preventing them from interfering with the titration. 3:33
• Pattinson's indicator is used instead of Eriochrome Black T because it functions effectively at a pH of 12.5, whereas Eriochrome Black T is only successful up to pH 10 or 10.5. 4:15
• At the endpoint, the color changes to clear blue because EDTA displaces the indicator from the calcium complex, and the blue color is due to the free indicator. 5:05
• The initial color of the solution after adding the indicator is wine red due to the formation of a complex between calcium ions and the indicator. 5:08
• Cement is a binding material used in construction, produced by calcining limestone and clay, with major constituents being calcium oxide and silica. 5:53
• A good quality cement should contain approximately 70-75% calcium oxide, with silica and other constituents present in trace amounts. 6:22
• Gypsum is an additive, not a constituent, added during the grinding of cement clinkers to act as a retarder, controlling the setting time and ensuring final strength. 7:56