44. Solving a chemistry problem

10. A standard solution of cerium was prepared by dissolving 0.0500 g of CeO2 in 25.00 ml of a mixture of perchloric and hydrochloric acids. In a flask with a capacity of 25.00 ml were placed: 2.50; 3.00; 3.50; 4.00; 4.50; 5.00 ml of standard solution, added ammonia, hydrogen peroxide, nitrilotriacetic acid and diluted to the mark with water. When photometry relative to the first solution received:
Vst, ml …………………. 3.00 3.50 4.00 4.50 5.0
Aotn ………………….. 0.135 0.270 0.405 0.545 0.680
A portion of lanthanide oxides weighing 0.0500 g was dissolved, the necessary reagents were added, and diluted, as in the construction of a calibration graph. Calculate the mass fraction (%) of CeO2 in the sample of lanthanide oxides according to the following data: 1) Arel..,x = 0.345; 2) Arel..,x = 0.440; 3) Arel..,x= 0.510; Answer: 1) 1.51%; 2) 1.65%; 3) 1.75%.