Two separate cylinders contain isotopically pure molecular chlorine

CHEMISTRY · Multi-part · A Level · Chemistry · Atomic structure · Atomic structure

Problem

Two separate cylinders contain isotopically pure molecular chlorine. Cylinder A holds

15.00\,\text{g}

^{35}

_2

(70.90\,\text{g\,mol}^{-1})

, and Cylinder B holds

20.00\,\text{g}

^{37}

_2

(74.97\,\text{g\,mol}^{-1})

. The gases are fully transferred into an evacuated vessel and allowed to mix. A chemist then withdraws

50.0\,\text{mmol}

of the molecular chlorine mixture, which is assumed to have a uniform isotopic composition identical to that of the bulk mixture. (a) Determine the amount of substance (in moles) of

^{35}

_2

and of

^{37}

_2

present in the vessel immediately after mixing but before any withdrawal. (b) Calculate the total number of chlorine atoms (not molecules) present in the vessel at this stage. Present the value in scientific notation and include units. (c) Compute the amount (in moles) of each isotopic molecule removed and the amount of each remaining in the vessel after the

50.0\,\text{mmol}

sample is withdrawn. (d) Using your results from part (c), evaluate the mass percent of

^{37}

Cl in the remaining gas. Explain the steps taken to arrive at this value.

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