Question

When \(3.06 \mathrm{g}\) hydrogen was allowed to react with an excess of oxygen, \(27.35 \mathrm{g}\) water was obtained. In a second experiment, a sample of water was decomposed by electrolysis, resulting in \(1.45 \mathrm{g}\) hydrogen and 11.51 g oxygen. Are these results consistent with the law of constant composition? Demonstrate why or why not.

Short answer

Yes, the results are consistent with the law of constant composition. This is proven by the fact that the percentage composition of hydrogen and oxygen in water from both experiments is the same: approximately \(11.2\%\) of hydrogen and \(88.8\%\) of oxygen. This consistency in percentage composition regardless of the source or preparation of the compound is precisely what the law of constant composition states.

Step-by-step solution

Calculate the mass of oxygen in the first experiment

Firstly, calculate the mass of oxygen in the first experiment. Since hydrogen reacts with oxygen to produce water and the total mass of water is given, the mass of oxygen can be calculated as the difference between the mass of water and the mass of hydrogen. Substract \(3.06 \mathrm{g}\) (mass of hydrogen) from \(27.35 \mathrm{g}\) (mass of water) to get \(24.29 \mathrm{g}\) of oxygen.

Calculate the percentage of hydrogen and oxygen in the first experiment

Next, calculate the percentage composition of hydrogen and oxygen. This is done by dividing the mass of each element by the total mass of the substance, and then multiplying by 100. Here the total mass is \(27.35 \mathrm{g}\). Dividing \(3.06 \mathrm{g}\) (mass of hydrogen) by \(27.35 \mathrm{g}\), and then multiplying by 100 gives approximately \(11.2\%\). Similarly, calculating for oxygen gives approximately \(88.8\%\).

Calculate the percentage of hydrogen and oxygen in the second experiment

Now calculate the percentage composition of hydrogen and oxygen in the second experiment, same as in step 2. The total mass in this case is \(1.45 \mathrm{g}\) (mass of hydrogen) + \(11.51 \mathrm{g}\) (mass of oxygen) = \(12.96 \mathrm{g}\). Calculating the percentages gives approximately \(11.2\%\) for hydrogen and \(88.8\%\) for oxygen.

Compare the outcomes

Lastly, compare the percentage compositions from the two experiments. If they're the same for both hydrogen and oxygen (which they are in this case), this is consistent with the law of constant composition, confirming there's no violation of this law.

Key concepts

Chemical Reactions

During a chemical reaction, substances interact to form new substances with different properties. Chemical reactions involve the breaking and forming of chemical bonds. In the exercise, hydrogen and oxygen react to form water. This is described by the balanced chemical equation: \[ 2 ext{H}_2 + ext{O}_2 ightarrow 2 ext{H}_2 ext{O} \]Here, two molecules of hydrogen gas react with one molecule of oxygen gas to yield two molecules of water. This reaction showcases the transformation from reactants (hydrogen and oxygen) to a product (water). It's a foundational principle that helps us understand how different elements can combine in accordance with specific ratios dictated by the balanced equation. The adherence to these quantities ensures consistency across different experiments.

Mass Percentage Composition

Mass percentage composition helps us identify the proportion of each element present in a compound. It provides insight into the specific makeup of a substance. Calculating mass percentage composition involves dividing the mass of a component by the total mass of the compound and multiplying by 100. For instance, in the exercise, the mass percentage of hydrogen in water from the first experiment is calculated as: \[ \left( \frac{3.06 ext{ g}}{27.35 ext{ g}} \right) \times 100 \approx 11.2\% \]For oxygen, it's: \[ \left( \frac{24.29 ext{ g}}{27.35 ext{ g}} \right) \times 100 \approx 88.8\% \]Understanding mass percentage composition is crucial as it allows chemists to determine the empirical formula of compounds and confirm the consistency of compound formation under different conditions.

Chemical Laws

The law of constant composition, also known as the law of definite proportions, states that a given chemical compound will always contain the same elements in the same proportions by mass, regardless of the sample size or source. This principle is fundamental in chemistry because it illustrates the predictable nature of chemical compounds. In the exercise, by comparing the percentage compositions of hydrogen and oxygen in different experiments resulting in water formation, we find the values consistent (11.2% hydrogen, 88.8% oxygen). This confirms the application's fidelity to the law of constant composition. Such regularities underpin the predictability and reliability of chemical formulations, enabling chemists to anticipate the outcomes of chemical reactions with precision.

Water Formation

Water formation is a classic example of a chemical reaction that demonstrates the law of constant composition. Water is composed of hydrogen and oxygen in a standard 2:1 ratio by molecule. During the reaction, each molecule of water contains two atoms of hydrogen and one atom of oxygen. In the problems presented, both experiments confirm water's consistent composition. In both trials, water's percentage composition by mass remains static, reinforcing the predictability and uniformity mandated by the law of constant composition. This stability in chemical makeup in different scenarios shows why water formation serves as a reliable illustration of fundamental chemical laws. Understanding water formation through these experiments highlights how profound and consistent chemical relationships drive natural and industrial processes alike.