Question

1. two compounds of hydrogen and oxygen are tested. compound i contains 15.0 g of hydrogen and 120.0 g of oxygen. compound ii contains 2.0 g of hydrogen and 32.0 g of oxygen.

a. determine the ratio of the mass of oxygen to the mass of hydrogen in each of the compounds.
b. why are the compounds not the same?
c. what is significant about these mass ratios?
d. if compound i is water, what could be the formula of compound ii?

Explanation:

Part (a)

Step1: Calculate ratio for Compound I

For Compound I, mass of oxygen ($m_{O1}$) = 120.0 g, mass of hydrogen ($m_{H1}$) = 15.0 g.
Ratio $r_1 = \frac{m_{O1}}{m_{H1}} = \frac{120.0}{15.0} = 8$.

Step2: Calculate ratio for Compound II

For Compound II, mass of oxygen ($m_{O2}$) = 32.0 g, mass of hydrogen ($m_{H2}$) = 2.0 g.
Ratio $r_2 = \frac{m_{O2}}{m_{H2}} = \frac{32.0}{2.0} = 16$.

Compounds have different chemical formulas (different ratios of H to O), so they are different substances (e.g., water $H_2O$ vs. hydrogen peroxide $H_2O_2$ have different H:O ratios).

Mass ratios reflect the law of multiple proportions: when two elements form multiple compounds, masses of one element (O) combining with a fixed mass of the other (H) are in simple whole - number ratios. Here, for a fixed H mass, O masses (or ratios) are in whole - number ratio (8:16 = 1:2), supporting this law.

Answer:

Ratio for Compound I: $\boldsymbol{8}$, Ratio for Compound II: $\boldsymbol{16}$

Part (b)