Question

general chemistry i
aleks - session closed
aleks - cristabel cortez - learn
measurement and matter
distinguishing mixtures from pure substances through physical properties
0/5
cristabel
read the descriptions below of two substances and an experiment on each. decide whether the result of the experiment tells you the substance is a pure substance or a mixture, if you can.
sample a is 100. ml of a clear liquid. the density of the liquid is measured, and turns out to be 0.77 g/ml. the liquid is then heated in a flask until it boils. the vapor that rises off the boiling liquid is collected for 10 minutes and cooled until it condenses into a separate beaker. the density of the liquid that remains in the flask is then measured, and turns out to be 1.04 g/ml.
sample b is a solid yellow cube with a total mass of 50.0 g. the cube is put into a beaker filled with 250. ml of water. the cube collapses into a small pile of orange powder at the bottom of the beaker. when this powder is filtered out, dried and weighed, it has a total mass of 29.9 g. if the experiment is repeated with 500. ml of water, the powder that’s left over has a mass of 30.0 g.
is sample a made from a pure substance or a mixture?
if the description of the substance and the outcome of the experiment isn’t enough to decide, choose \cant decide.\
pure substance
mixture
(cant decide)
is sample b made from a pure substance or a mixture?
if the description of the substance and the outcome of the experiment isn’t enough to decide, choose \cant decide.\
pure substance
mixture
(cant decide)

Explanation:

Step1: Analyze Sample A

A pure substance has a constant density throughout a phase - change process. In Sample A, the initial density of the liquid is 0.77 g/mL and the density of the liquid remaining in the flask after boiling is 1.04 g/mL. Since the density changes during the boiling process, it indicates that the composition of the substances in the liquid has changed. This is characteristic of a mixture.

Step2: Analyze Sample B

A pure substance would dissolve or react in a consistent way in a given solvent. For Sample B, when the solid yellow cube is put into water, it collapses and a non - consistent amount of powder is left over initially (29.9 g in 250 mL of water and 30.0 g in 500 mL of water). This non - uniform behavior suggests that the solid is a mixture.

Answer:

Is sample A made from a pure substance or a mixture? - mixture
Is sample B made from a pure substance or a mixture? - mixture