Question

A chemist decomposes several samples of water into hydrogen and oxygen gas and determines the mass of the hydrogen and oxygen obtained.

Sample Number    Grams of Hydrogen        Grams of Oxygen

1                                 1.5                                      12.0

2                                  2.0                                      16.0

3                                  2.5                                      20.0

Summarize these observations in a short statement.

Next the chemist decomposes several samples of carbon dioxide into carbon and oxygen. Again, she determines the mass of each gas produced.

Sample Number    Grams of Carbon    Grams of Oxygen    Ratio (C to O)

1                                 0.5                              1.3                               0.385

2                                 1.0                              2.7                               0.37

3                               1.5                              4.0                               0.375

b.      Summarize these observations in a short statement.

c.       Formulate a law from the observations in (a) and (b).

d.    Formulate a theory that might explain your law in (c).

d.    Formulate a theory that might explain your law in (c).

Answer 1

a) The observation is that even though there are twice as many hydrogens than there are oxygens in a molecule of water (H2O), that the oxygen has much more mass than the hydrogen , so in each measurement, the oxygen collection weighs much more than the hydrogen even though there are half as many of them. In fact one molecule of oxygen gas (O2) weighs 32g a mole, compared to hydrogen gas (H2) , which has a weight of 2 grams a mole.

b) When the chemist separates carbon and oxygen from CO2, the carbon remains a single atom, so that one mole of carbon has a mass of 12g a mole. The oxygen on the other hand,never stays a single atom but instead turns into a oxygen gas molecule, two oxygens bonded together, so that decomposing the CO2 gives you one mole of carbon at 12 grams a mole, and at the same time you get 32 grams of oxygen gas.

c) A law from the observations is that when you decompose water or CO2, that the mass of the collected constituents is based on the mass of the formed gases or solids. Such that oxygen is always found in the O2 state, not a single oxygen, and hydrogen is also H2, not single hydrogens. But the carbon will be found as a single atom solid.

In summary, the law is oxygen and hydrogen always form double atomed gas molecules, H2 or O2, when you decompose either water or carbon dioxide

d) Oxygen gas and hydrogen gas are much more stable as a gas than remaining as a single atom of H+ or O- -. In nature all chemicals try to go to the lowest energy level possible. In this case, oxygen and hydrogen gas has a lower energy level than the individual atoms would have. The individual atoms are highly reactive and won't stay that way in nature. They immediately bond with each other to form the respective gases.