In the laboratory a student named Georgia weighed 4.75 g ofan unknown solid mixt

Question

In the laboratory a student named Georgia weighed 4.75 g ofan unknown solid mixture containing benzoic acid, copper (II)sulfate, and sand. She added 15 mL of acetone to her sample anddissolved one of the components of the mixture.

She then filters this component to seperate ifout from the others (still dissolved insolution). She weighs thecomponent and finds it to weigh 2.65 g.

What is the percent composition of this component in themixture?

She then weighs this water-soluble component and finds ithas a mass of 2.20 g.

What is the percent composition of this component in themixture?

The third component was insoluble in both acetone andwater. Drying and weighing this component she it finds it has amass of 0.46 g.

What is the percent composition of this insuluble component of themixture?

Explanation / Answer

You know that the mixture consists of benzoic acid, coppersulfate, and sand, and you know that the overall sample of themixture weighs 4.75 g. Percent composition equals (mass ofcomponent/total sample mass) * 100%. So, Georgia first added acetone to dissolve one of thecomponents, probably benzoic acid. After filtering, she findsthat the dissolved component weighs 2.65 g. So, the percentcomposition of this component in the mixture is (2.65 g/4.75 g) *100% = 55.8%. Next, Georgia extracts the mixture with water and dissolvesone of the other components, probably copper sulfate. Afterfiltering, she finds that the water-soluble component weighs 2.20g. So, the percent composition of the water-soluble componentis (2.20 g/4.75 g) * 100% = 46.3%. Finally, Georgia takes the last component that was not solublein acetone or water. This component is certainly sand. She weighs it and finds that it weighs 0.46 g. So, thepercent composition of this insoluble component is (0.46 g/4.75 g)* 100% = 9.7% Now, the problem is that when you add these percentagestogether, you get 111.8%. This is impossible. Georgiashould not get more than 100%. What has most likely happenedis that Georgia did not dry the components completely before sheweighed them. The extra mass is probably caused by water andacetone that was not completely dried off. The only otherexplanation as to why Georgia would get more than 100% is that shemay have weighed the mixture or the components incorrectly. Hope this helps.

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