Question

a sample of an unknown pure substance x is analyzed and found to contain 9.34 g of element e1, 10.7 g of element e2, and no other elements. a similar analysis is made of three other substances that also only contain elements e1 and e2. the results are shown in the table below. decide whether each of the other substances is also a pure substance. if you dont have enough information to decide, choose cant decide.

substance	mass of e1	mass of e2	pure substance?
b	14.7 g	19.3 g	pure substance (cant decide) mixture (cant decide)
c	31.3 g	22.7 g	pure substance (cant decide) mixture (cant decide)

Explanation:

Step1: Recall the law of definite proportions

In a pure substance, the ratio of the masses of the elements is constant. For substance A: The ratio of mass of \(E_1\) to mass of \(E_2\) is \(\frac{21.1}{20.9}\approx1.01\). For substance B: The ratio of mass of \(E_1\) to mass of \(E_2\) is \(\frac{14.7}{19.3}\approx0.76\). For substance C: The ratio of mass of \(E_1\) to mass of \(E_2\) is \(\frac{31.3}{22.7}\approx1.38\).

Step2: Analyze the results

Since the ratios of the masses of \(E_1\) and \(E_2\) are different for substances A, B and C, they cannot be the same pure - substance. A pure substance has a fixed composition by mass of its elements. So these are mixtures.

Answer:

A. mixture
B. mixture
C. mixture