Potassium permanganate can be used as a disinfectant. How would you prepare \(25.0 \mathrm{~L}\) of a solution that is \(15.0 \% \mathrm{KMnO}_{4}\) by mass if the resulting solution has a density of \(1.08 \mathrm{~g} / \mathrm{mL}\) ? What is the molarity of the resulting solution?

Short Answer

Expert verified
Answer: To achieve a 15.0% concentration by mass, 4050 g of Potassium permanganate needs to be added. The molarity of the resulting solution is 1.025 mol/L.

Step by step solution

01

Calculate the total mass of the solution.

Given the density of the solution and the final volume, we can calculate the total mass as follows: Density = Mass / Volume We can rearrange the formula to find the mass: Mass = Density × Volume Given the density of 1.08 g/mL and a volume of 25.0 L (which is equal to 25000 mL), the mass can be calculated as: Mass = 1.08 g/mL × 25000 mL = 27000 g
02

Calculate the mass of KMnO4 required.

Now, we can determine the mass of KMnO4 needed to achieve a 15.0% concentration by mass: Mass of KMnO4 = (Percentage × Total Mass) / 100 Mass of KMnO4 = (15.0 × 27000 g) / 100 = 4050 g
03

Determine the number of moles of KMnO4.

To calculate the number of moles of KMnO4, we can use the formula: Moles = Mass / Molar Mass The molar mass of KMnO4 is 39.098 + (15.999 × 4) + (54.938) = 158.034 g/mol. Number of moles = 4050 g / 158.034 g/mol = 25.63 moles
04

Calculate the molarity of the solution.

Finally, we can calculate the molarity of the solution as follows: Molarity = Moles / Volume (in liters) Molarity = 25.63 moles / 25.0 L = 1.025 mol/L The resulting solution has a molarity of 1.025 mol/L.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Solution Concentration
Understanding solution concentration is key in chemistry, especially when preparing a specific solution like potassium permanganate, which can be used as a disinfectant. Concentration describes how much of a substance is present in a certain amount of solvent. There are several ways to express this, but the most common is by mass percent (mass %), volume percent, molarity, and molality.

For mass percent, this indicates the mass of solute (in this case, KMnO₄) present per 100 grams of the solution. The provided problem states that we want to prepare a solution with a mass percent of 15.0%. It means that for every 100 grams of our potassium permanganate solution, 15 grams will be KMnO₄, and the remaining 85 grams will be water or other solvents present.
Molarity Calculation
When dealing with solutions, molarity is an essential concept to grasp. It measures the concentration of a solution by describing the number of moles of solute per liter of solution. The formula to calculate molarity is:
\[ M = \frac{n}{V} \]
where \( M \) is the molarity, \( n \) is the number of moles of the solute, and \( V \) is the volume of the solution in liters. In the exercise, we already determined the number of moles of KMnO₄ and the volume of the solution required. By dividing the number of moles by the volume, we can calculate the molarity of the potassium permanganate solution. This step is critical for various applications where a precise concentration is necessary, such as in lab settings, industrial processes, or medical treatments.
Solution Preparation by Mass Percent
Preparing a solution based on mass percent involves calculating the exact weight of the solute and solvent required to reach the desired concentration. The process involves multiple steps that must be meticulously followed to ensure accuracy. To prepare a 15.0% KMnO₄ solution by mass, first, we need to find the total mass of the solution using the given density and desired volume. Then, we calculate 15.0% of this total mass to determine the mass of KMnO₄ we need to weigh out.

To further clarify, if we have 27,000 grams of our final solution and we want a 15.0% concentration, we need to calculate 15.0% of 27,000 grams, which is 4,050 grams of KMnO₄. The remaining mass will be the mass of the water or other components of the solution. It's important to ensure that all equipment used for measurement is calibrated and that temperature, which can affect density, is considered during preparation.

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