Question

You have two solutions of chemical A. To determine which has the highest concentration of A (molarity), which of the following must you know (there may be more than one answer)? a. the mass in grams of A in each solution b. the molar mass of A c. the volume of water added to each solution d. the total volume of the solution Explain.

Short answer

To determine which solution has the highest concentration (molarity) of chemical A, you need to know: - the mass in grams of A in each solution (Option a) - the molar mass of A (Option b) - the total volume of the solution (Option d) Option c (the volume of water added) is not necessary.

Step-by-step solution

Molarity Formula

Molarity (M) is the number of moles of solute (in our case, chemical A) per liter of solution. The formula to calculate molarity is: M = moles of solute / liters of solution Therefore, to compare the molarity of the two solutions, we must know: 1. The number of moles of chemical A in each solution 2. The total volume of each solution Now, let's analyze each option to see if they provide the required information to calculate molarity.

Option a: mass in grams

Knowing the mass in grams of chemical A in each solution does not directly provide the number of moles. However, it is related and can be used in combination with the molar mass (Option b) to find the number of moles. Without the molar mass, Option a alone does not provide enough information to calculate molarity.

Option b: molar mass

The molar mass of a substance is the mass of one mole of that substance. This information helps us convert the mass of chemical A in grams (Option a) to the number of moles. Thus, the molar mass is necessary for calculating molarity when given the mass of the solute, but it is not sufficient on its own.

Option c: volume of water added

Knowing the volume of water added to each solution does not provide enough information to find the total volume of the solution, as it only considers the solvent (water) and not the solute (chemical A). Therefore, this option alone is not enough to calculate molarity.

Option d: total volume of the solution

The total volume of the solution is an essential factor for calculating molarity, as it is needed in the denominator of the molarity formula. This option, when combined with the number of moles of the solute or the information required to obtain it (Options a and b), allows us to calculate molarity.

Conclusion

To find out which solution has the highest concentration (molarity) of chemical A, we need to know: - the mass in grams of A in each solution (Option a) - the molar mass of A (Option b) - the total volume of the solution (Option d) Therefore, the correct answers are a, b, and d. Option c (the volume of water added) is not necessary to determine which solution has the highest molarity of chemical A.

Key concepts

Moles of Solute

Understanding the concept of moles is crucial when working with solutions and molarity. In chemistry, a mole is a unit that measures the amount of a substance. When we refer to the "moles of solute," we are discussing how many moles of a particular substance, in this case, chemical A, are present in a solution. To calculate the molarity of a solution, we must first determine the number of moles of the solute. This is done by using the formula:\[\text{Moles of solute} = \frac{\text{mass of solute (in grams)}}{\text{molar mass (g/mol)}}\]By knowing the moles of solute, we can then proceed to calculate the molarity. This relationship highlights why a precise understanding of moles is indispensable for concentration calculations.

Molar Mass

Molar mass is a key concept when determining the moles of a substance from its mass. It is defined as the mass of one mole of a given substance, usually expressed in grams per mole (g/mol). Using molar mass, we can convert the mass of chemical A into moles. This conversion follows the basic principle that:

• 1 mole of a substance = molar mass in grams

Thus, if you know the mass of chemical A in grams and its molar mass, you can find the number of moles of A. This is crucial because moles directly relate to the calculation of the solution's molarity. Understanding the concept of molar mass is essential for transforming mass information into a form that can be used for further calculations.

Volume of Solution

The volume of a solution is another fundamental aspect of calculating molarity. It is the total amount of solution in which the solute is dissolved, typically measured in liters.When determining molarity, the volume of the solution is used as the denominator in the formula:\[\text{Molarity (M)} = \frac{\text{moles of solute}}{\text{liters of solution}}\]Hence, without knowing the total volume of the solution, it is impossible to calculate the molarity accurately. This volume includes both the solute and the solvent, so it's crucial to consider the complete solution rather than just the volume of solvent, like water, added. Accurate volume measurement is essential for ensuring the correct concentration calculations.

Concentration Comparison

In chemistry, comparing concentrations is essential to understanding the relative amounts of substances in solutions. When we talk about molarity, we are directly comparing the concentration of the solute in different solutions. To compare which solution has a higher concentration of chemical A, knowing the moles of solute and the total volume of each solution is necessary. The formula for molarity — moles of solute per liter of solution — allows us to make these comparisons effectively. Higher molarity means more moles of solute per liter, indicating a stronger concentration. Thus, accurately comparing concentrations requires complete data on moles and volume, enabling clear determinations of which solution is more concentrated.