Question

A substance was analyzed in a laboratory. It was composed of three elements in a fixed ratio. The substance is an ?

Answer 1

Explanation:

A compound is defined as the substance which contains different type of elements that chemically combine together in a fixed ratio by mass.

For example, $CaCl_{2}$ is a compound as it contains calcium and chlorine which are different elements. And, both Ca and Cl are combining in 1:2 ratio.

And, for every molecule of calcium chloride these elements will always be present in 1:2 ratio.

Thus, we can conclude that when a substance was analyzed in a laboratory. It was composed of three elements in a fixed ratio. The substance is a compound.

Answer 2

The element strontium (atomic number = 38) has four naturally-occurring isotopes. They are: Isotope / Percent Abundance / Mass (amu) Sr-84 / 0.56% / 83.9134 Sr-86 / 9.86% / 85.9093 Sr-87 / 7.00% / 86.9089 Sr-88 / 82.58% / 87.9056 The first thing to do is to convert all of the percentages to decimal fractions. To do that just move the decimal point two places to the left. Be careful, though...if the decimal is already at the front of the number you STILL have to move it two places. Add leading zeroes as necessary. 0.56% becomes 0.0056 9.86% becomes 0.0986 7.00% becomes 0.0700 82.58% becomes 0.8258 Next multiply each of the decimal fractions by the mass of each isotope. 0.0056 x 83.9134 = 0.47 0.0986 x 85.9093 = 8.47 0.0700 x 86.9089 = 6.08 0.8258 x 87.9056 = 72.59 Finally add the results to find the average atomic mass. 0.47 + 8.47 + 6.08 + 72.59 = 87.61 amu This agrees closely with the listed atomic mass for strontium, so I know I probably did my work correctly. I hope that helps