草酸钙结晶沉淀条件对白云石中钙含量测定的影响

doi:10.3866/PKU.DXHX202208028

Abstract

Abstract:

"Determination of calcium content in dolomite by potassium permanganate method" is a classical analytical chemistry experiment to train students' comprehensive experimental ability, including dissolution of dolomite ore sample, preparation and washing of calcium oxalate precipitate, concentration calibration of potassium permanganate solution and titration of calcium oxalate precipitate. Because of the complexity of the experiment process and the many influence factors, it is very difficult that students control the measurement error within 3‰ in the experiment. Therefore, we guide students to precipitate calcium oxalate from acid-dissolved dolomite solution under different experimental conditions, investigate the relationship between the particle size and surface morphology of calcium oxalate precipitate and the determined calcium contents, and thus revealing the control factors affecting the accuracy of calcium content determination. It not only deepens the students' understanding to the experimental process, but also stimulates their interest in learning chemical experiments, improving their experimental ability and strengthening their confidence in scientific research.

Key words: Potassium permanganate method, Redox titration, Calcium oxalate, Morphology, Titration error

Tianqi Liu, Yijie Liu, Tianwei Song, Dongsheng Liang, Qizhi Yao. Influence of Calcium Oxalate Precipitation on Determination of Calcium Content in Dolomite[J].University Chemistry, 2023, 38(8): 170-176.

组别	W_{Na₂C₂O₄}/g	V_KMnO₄/mL	c_KMnO₄/(mol∙L⁻¹)	相对偏差/‰	${\bar c}$_KMnO₄/(mol∙L⁻¹)
1	0.1863	25.95	0.02143	1.06	0.02141
2	0.1602	22.35	0.02140	−0.53
3	0.1597	22.28	0.02140	−0.52

组别	沉淀条件	W_白云石/g	V_KMnO₄/mL	w% (CaO)	相对误差/‰^*
样品1	90 ℃、滴加速率2 mL∙min⁻¹、陈化1 h	0.2646	30.90	35.05	0.86
	90 ℃、滴加速率2 mL∙min⁻¹、陈化1 h	0.2303	26.92	35.08	1.71
样品2	90 ℃、滴加速率2 mL∙min⁻¹、直接过滤	0.2143	25.15	35.22	5.71
	90 ℃、滴加速率2 mL∙min⁻¹、直接过滤	0.2154	25.32	35.28	7.42
样品3	25 ℃、一次添加、陈化1 h	0.2286	26.90	35.32	8.57
	25 ℃、一次添加、陈化1 h	0.2253	26.52	35.33	8.85

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Influence of Calcium Oxalate Precipitation on Determination of Calcium Content in Dolomite

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