One step in the purification of zinc from ZnS ore is the following reaction with

Question

One step in the purification of zinc from ZnS ore is the following reaction with oxygen. 2 ZnS(s) + 3 O2(g) ? 2 ZnO(s) + 2 SO2(g)

A 20.0-L flask initially contains O2 at a pressure of 694 torr and a temperature of 35.0C. Then 20.18 g of solid ZnS is added, and the reaction above goes to completion. If the temperature at the end of the reaction is 57.0C, what will be the final total pressure in the flask? (Assume that the volume(s) of any solids present are small enough to neglect, so that the gas volume is 20.0 L throughout the reaction.)

Explanation / Answer

mass of ZnS=20.18 g

moles of ZnS=mass/molar mass=20.18g/97.47 g/mol=0.21 moles

from the reaction 2 ZnS(s) + 3 O2(g) ? 2 ZnO(s) + 2 SO2(g)

2 moles of SO2=2 moles of ZnS

so ,moles of SO2 present on completion of reaction=moles of ZnS=0.21 moles

The flask has gas,n=0.21 moles

                      T=57C=273+57=330K'

                        R=Universal gas constant=0.0821 L atm/K mol

                       V=20 ml

using ideal gas equation=PV=nRT

                                       P=nRT/V=0.21 moles* 0.0821 L atm/K mol *330K * (760 torr/atm)/20L=216.202 torr

                           pressure=216.202 torr

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