Problem 22 - Chemistry Matter and Change

Question

Two unknown compounds 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. Are the compounds the same? Explain your answer

Step-by-Step Solution

Answer

The two compounds are not the same because the mass ratio of oxygen to hydrogen for Compound I is 8, and for Compound II, it is 16. The difference in mass ratios indicates that the combination of hydrogen and oxygen in the compounds is not the same, and they must be different compounds.

Step 1: Calculate the mass ratios for both compounds

To begin, we will calculate the mass ratio of oxygen to hydrogen for both Compounds I and II. This is done by dividing the mass of oxygen by the mass of hydrogen in each compound. For Compound I: Mass ratio of O to H = \( \frac{mass \, of \, oxygen}{mass \, of \, hydrogen} \) For Compound II: Mass ratio of O to H = \( \frac{mass \, of \, oxygen}{mass \, of \, hydrogen} \)

Step 2: Determine the mass ratios for both compounds

Next, we will plug in the given masses of hydrogen and oxygen in the compounds and determine the mass ratios. For Compound I: Mass ratio of O to H = \( \frac{120.0 \, g}{15.0 \, g} = 8 \) For Compound II: Mass ratio of O to H = \( \frac{32.0 \, g}{2.0 \, g} = 16\)

Step 3: Compare the mass ratios

Now, we need to compare the mass ratios of oxygen to hydrogen for both compounds. For Compound I: Mass ratio of O to H = 8 For Compound II: Mass ratio of O to H = 16 The mass ratio of oxygen to hydrogen for Compound I is 8, whereas the mass ratio for Compound II is 16. These values are not equal.

Step 4: Drawing conclusion

Since the mass ratio of oxygen to hydrogen in Compound I and Compound II are different, we can conclude that the two compounds are not the same. The difference in mass ratios indicates that the combination of hydrogen and oxygen in the compounds is not the same and they must be different compounds.

Key Concepts

Mass Ratio Calculation

Understanding the concept of mass ratio calculation is vital when it comes to distinguishing between different chemical compounds. Mass ratio, essentially, is the comparison of the mass of one element to the mass of another within a compound. In the given problem, two compounds are analyzed to determine if they are the same based on the mass ratio of oxygen to hydrogen.

How do you perform a mass ratio calculation? Let's start with the basics:

• Identify the masses of the individual elements in a compound from the problem or by experiment.
• Choose the element for which you want to calculate the mass ratio with respect to the other.
• Divide the mass of the first element by the mass of the second to obtain your mass ratio: \( mass \, ratio = \frac{mass \, of \, element \, A}{mass \, of \, element \, B} \).

To improve comprehension, remember the mass ratio is simply a way to express how much of one element is present compared to another in a substance, and it's often a useful step in identifying a compound or comparing different compounds.

For the problem in the exercise, by calculating the mass ratios for each compound separately and then comparing them, we can determine that the ratios are not equal, hence the compounds are distinct. This comparison uses a basic understanding of proportionality within chemical substances and is a fundamental aspect of chemical analysis.

Empirical Formula Determination

Empirical formula determination is a step up from the basic mass ratio calculation. It allows us to find the simplest whole number ratio of atoms in a compound. This is a cornerstone concept in chemistry because it provides a foundational representation of a chemical substance.

Here's a brief guide to determining an empirical formula:

• Measure the mass of each element present in the compound.
• Convert these masses to moles using the atomic mass units (amu) of each element.
• Find the simplest ratio of the moles of elements to each other by dividing by the smallest number of moles calculated.
• Round the resulting ratios to the nearest whole numbers to achieve the empirical formula.

While the exercise provided doesn't require finding the empirical formula, it's an important concept to understand as it is closely related to mass ratios. If the exercise were extended to require the empirical formula, the mass ratio calculation would be a stepping stone to finding the ratio of moles of hydrogen to oxygen. The resulting whole number ratio defines the empirical formula which represents the fundamental composition of the compound.

Stoichiometry

Stoichiometry is a broad term that relates to the quantitative relationships between the substances as they participate in chemical reactions. This takes both mass ratio calculations and empirical formulas into account to predict the amounts of products and reactants.

To apply stoichiometry, you should:

• Know the balanced equation for the chemical reaction involved.
• Use the mole concept to understand the relationship between reactants and products.
• Use the molecular or empirical formulas of substances to convert between grams and moles.
• Understand that stoichiometry is how we translate the language of chemical equations into tangible amounts of substances.

For instance, after calculating mass ratios and determining empirical formulas, you can then relate these to the amount of substance produced or required in reactions. Even though our original exercise doesn't directly involve a stoichiometric calculation, understanding this concept facilitates a more profound grasp of how elements and compounds interact during chemical reactions, ultimately shaping the world on a molecular level.