1. Chlorine has two isotopes, 35 Cl and 37 Cl. 37 Cl weighs 37.00 amu and 35 Cl

Question

1. Chlorine has two isotopes, 35Cl and 37Cl. 37Cl weighs 37.00 amu and 35Cl weighs 35.00 amu. What is the percent abundance of 35Cl? The average atomic mass of Cl is 35.45 amu.

2.

A student wants to identify a clear colorless liquid by determining the density. She first weighs an empty flask (60.1 g). She then adds 100.00 mL of the unknown liquid to it. The flask now weighs 138.1 g. Can the student identify the liquid from the 4 listed below? If so, which is it?
Butane: 0.601 g/mL
Gasoline: 0.780 g/mL
Water: 1.00 g/mL
Phosgene: 1.381 g/mL

Explanation / Answer

1. averageatomicmass = atomicmass*x + atomicmass*1-x

35.45 = 35*(1-x)+(37*x)

x = 0.225

so that,

percent abundance of 35Cl = 1-x = 1-0.225 = 0.775

= 0.775*100 = 77.5%

2.   mass of 100 ml sample   = 138.1 - 60.1 = 78 grans

    Volume of sample = 100 ml

Density of sample = 78/100 = 0.78 g/ml

so that, sample = gasoline : 0.78 g/ml

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