Question

a sample of an unknown pure substance x is analyzed and found to contain 7.94 g of element e1, 9.06 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 a pure substance. if you dont have enough information to decide, choose cant decide.

substance	mass of e1	mass of e2	pure substance?
b	19.1 g	18.9 g	o pure substance o mixture o (cant decide)
c	12.5 g	16.5 g	o pure substance o mixture o (cant decide)

Explanation:

Step1: Recall the law of constant composition

A pure substance has a fixed - ratio of elements by mass. For a sample to be a pure substance, the ratio of the masses of the elements in different samples should be the same.

Step2: Calculate the ratio of $E_1$ to $E_2$ for each substance

For substance A: $\frac{\text{mass of }E_1}{\text{mass of }E_2}=\frac{14.6}{8.36}\approx1.75$
For substance B: $\frac{\text{mass of }E_1}{\text{mass of }E_2}=\frac{19.1}{18.9}\approx1.01$
For substance C: $\frac{\text{mass of }E_1}{\text{mass of }E_2}=\frac{12.5}{16.5}\approx0.76$

Step3: Analyze the results

Since the ratios of the masses of $E_1$ to $E_2$ are different for substances A, B and C, they cannot be the same pure substance. Each sample has a different ratio of the two elements, so they are mixtures.

Answer:

A. mixture
B. mixture
C. mixture