What is the concentration of of Cr (MM=51.9962 g/mol) in ppm in the 250.0 mL flask?

[匿名]

2017-09-24 7:57 pm

A dried sample of K2Cr2O7 (MM=294.1850 g/mol) weighing 1.0000 g was dissolved in 1.100 L in 1.0 M H2SO4. A 25.00 mL aliquot of this sample was diluted to 200.0 mL. From the 200.0 mL flask a 25.00 mL aliquot was removed and diluted to 250.0 mL.

回答 (1)

wanszeto

2017-09-24 10:15 pm

✔ 最佳答案

Mass of Cr in the 1.0000-g sample
= (1.0000 g) × (2 × 51.9962 / 294.1850)
= 0.35349 g

As the final 250-mL solution is very dilute, density of the final 250-mL solution
= Density of water
= 1.000 g/mL

Concentration of Cr in the final 250.0 mL solution
= (0.35349 g/ 1.100 L) × (25.00/200.0) × (25.00/250)
= (0.35349 g/ 1100 mL) × (25.00/200.0) × (25.00/250) / (1.000 g/mL)
= 4.017 × 10⁻⁶
= 4.017 ppm

====
OR: Concentration of Cr in the final 250.0 mL solution
= [(1.0000 g K₂Cr₂O₇) × (2 × 51.9962 g Cr / 294.1850 g K₂Cr₂O₇) / 1100 g solution)] × (25.00/200.0) × (25.00/250)
= 4.017 × 10⁻⁶
= 4.017 ppm

👍 3 👎 0