Question

If we consider that \(\frac{1}{6}\), in place of \(\frac{1}{12}\), mass of carbon atom is taken to be the relative atomic mass unit, the mass of one mole of a substance will: (a) Decrease twice (b) Increase two fold (c) Remain unchanged (d) Be a function of the molecular mass of the substance

Short answer

The mass of one mole would decrease twice, choice (a).

Step-by-step solution

Understanding the Problem

In this problem, we are asked to consider an alternative definition for the atomic mass unit (amu). Usually, the amu is defined as 1/12 the mass of a carbon-12 atom. The problem suggests we redefine it as 1/6 the mass instead.

Defining Molar Mass

Molar mass is the mass of one mole of a substance. This is typically calculated by summing the atomic masses of each element in a compound, measured in grams per mole. Typically, these are based on the standard atomic mass unit (1/12 of a carbon atom).

Impact of New AMU on Molar Mass

With the new definition, each amu represents twice the mass it did before, because 1/6 is twice as large as 1/12. As a result, the number representing the molar mass (in g/mol) would numerically decrease by half when measured under the new amu because each amu represents a larger actual mass.

Logical Conclusion

Therefore, with the new amu definition, the mass of one mole of the substance would numerically be half of what is calculated with the standard amu. Thus, the correct choice regarding how the molar mass would change is: (a) Decrease twice.

Key concepts

Understanding Molar Mass

Molar mass is a fundamental concept important for anyone delving into chemistry. It's essentially the mass of one mole of a substance, expressed in grams per mole (g/mol). To find the molar mass of a compound, you simply add together the atomic masses of all the atoms in a molecule. For instance, water (H₂O) has a molar mass of about 18 g/mol. This is calculated by adding twice the atomic mass of hydrogen (about 1 g/mol each) with the atomic mass of oxygen (about 16 g/mol).

This concept is crucial when performing chemical calculations because it connects the microscopic world of atoms and molecules to the macroscopic world, allowing us to weigh amounts of substances in a laboratory. Molar mass acts as a bridge, helping us convert between the number of atoms or molecules and mass, making chemical equations practically applicable. Always remember: by convention, calculations usually use the standard atomic mass unit, which is based on \(\frac{1}{12}\) the mass of a carbon-12 atom.

Grasping Relative Atomic Mass

Relative atomic mass tells us how heavy an atom is compared to a carbon-12 atom. It is a dimensionless quantity often shown on the periodic table as the weighted average of all isotopes of an element found on Earth. This average considers the prevalence of each isotope in nature.

You might wonder why it's 'relative'. The carbon-12 isotope is the standard reference, and everything else is compared to it. This definition provides a consistent way to compare different elements with diverse isotopes. For example, the relative atomic mass of chlorine (Cl) is about 35.5 because it averages out the masses of its two main isotopes (chlorine-35 and chlorine-37).

• It gives chemists a global standard for talking about atomic weight.
• It enables accurate chemical calculations.
• It lets one account for natural isotope variations among different samples.

Conducting Chemical Calculations

Chemical calculations can seem tricky at first, but understanding key concepts like molar mass and relative atomic mass can make them more manageable. These calculations allow chemists to predict the amounts of substances consumed and produced during reactions.

Chemists use the molar mass to convert between the mass of a substance and the number of moles, which is crucial when you're calculating reactant or product amounts. For example, if you know the mass of a sample solution, you can find out how many atoms, molecules, or moles it contains. You can also calculate the mass of products made in a chemical reaction from the mass of reactants used.

• First, find the molar mass of each substance involved in the equation.
• Next, use stoichiometry to keep track of mole ratios among reactants and products.
• Then, use equations and mole ratios to find out how much of one substance is related to another.
• Finally, convert your findings using molar mass back to grams or another practical unit.

In addition to straightforward mass-to-mole conversions, molar mass and relative atomic mass also become handy for other calculations, such as determining yields, concentrations, and rates of reactions. It all starts with mastering these initial building blocks of chemical math.