Problem 11 - Chemistry: Principles and Reactions

Question

Describe how you would prepare \(465 \mathrm{~mL}\) of \(0.3550 \mathrm{M}\) potassium dichromate solution starting with (a) solid potassium dichromate. (b) \(0.750 M\) potassium dichromate solution.

Step-by-Step Solution

Answer

= 0.165025 moles Now that we have the number of moles of potassium dichromate needed, we can determine the mass of the solid potassium dichromate required. #tag_title# (a) Calculate the mass of solid potassium dichromate)#tag_content# To calculate the mass of solid potassium dichromate, we'll use the formula: mass = moles * molar mass The molar mass of potassium dichromate (K2Cr2O7) is approximately 294.18 g/mol. Therefore, the mass of solid potassium dichromate needed is: mass = 0.165025 moles * 294.18 g/mol = 48.531 g #tag_title# (b) Calculate the volume of the 0.750 M potassium dichromate solution)#tag_content# To determine the volume of the 0.750 M potassium dichromate solution needed, we'll use the dilution formula: M1 * V1 = M2 * V2 Where M1 and V1 are the molarity and volume of the initial solution (0.750 M), and M2 and V2 are the molarity and volume of the final solution (0.3550 M and 0.465 L). We want to find V1. V1 = (M2 * V2) / M1 V1 = (0.3550 * 0.465) / 0.750 = 0.219382 L Therefore, we need 0.219382 L or 219.382 mL of the 0.750 M potassium dichromate solution. #Answer Format# (a) To prepare 465 mL of 0.3550 M potassium dichromate solution using solid potassium dichromate, 48.531 g of solid potassium dichromate is needed. (b) To prepare 465 mL of 0.3550 M potassium dichromate solution using a 0.750 M potassium dichromate solution, 219.382 mL of the 0.750 M solution is required.

Step 1: (a) Determine the number of moles needed)

To determine how much solid potassium dichromate we need, we'll first need to find the number of moles needed in the 465 mL solution at 0.3550 M concentration. To do so, we'll use the equation: M = moles of solute / volume of solution (in liters) Rearranging this formula for moles of solute: moles of solute = M * volume of solution (in liters) We're given M = 0.3550 M and volume = 465 mL (which is 0.465 L). moles of solute = 0.3550 * 0.465

Key Concepts

Molarity Calculation

Molarity, commonly denoted as M, is a way to express the concentration of a solute in a solution. It is defined as the number of moles of solute divided by the volume of the solution in liters. For example, if you have a solution with 0.3550 moles of potassium dichromate in a total volume of one liter, the molarity of that solution would be 0.3550 M.
To calculate molarity, you can use the equation \( M = \text{moles of solute} / \text{volume of solution in liters} \).
This formula can be rearranged when you need to find the number of moles required for a particular volume of solution. Just multiply the desired molarity by the volume of the solution in liters to get the number of moles of solute. This approach helps you understand how concentrated a solution is and determines how much of a chemical substance you'll need.

• Molarity helps in carrying out chemical reactions involving solutions.
• Knowing molarity allows you to dilute or concentrate solutions accurately.

Potassium Dichromate

Potassium dichromate, with a chemical formula of \( K_2Cr_2O_7 \), is a bright orange crystalline solid used in various applications. It's often employed in lab settings for chemical reactions and serves as an oxidizing agent. When preparing a solution of potassium dichromate, handling with care is necessary because it is toxic and can cause environmental harm.
One common use of this compound is in the analysis of alcohol concentrations through the dichromate oxidation method. Also, in school labs, it's used in titrations and experiments involving redox reactions due to its distinct color change when it reacts.
To safely prepare a solution, always follow safety protocols like wearing gloves and goggles. Potassium dichromate can irritate skin and eyes, so proper handling is crucial. Make sure to dispose of leftover solutions correctly, as they can pose a risk to the environment.

• Be aware of safety concerns while handling the chemical.
• Store the compound in a cool, dry place to maintain its stability.

Dilution Process

Dilution is the process of reducing the concentration of a solute in a solution, usually by adding more solvent. This process is essential when you have a stock solution that is too concentrated for your needs. By diluting, you can achieve the desired molarity for your experiments or applications.
To conduct a dilution, you need to know the initial concentration and volume of your stock solution, along with the final volume you want to achieve. The equation \( M_1 \times V_1 = M_2 \times V_2 \) helps in finding the right volumes or concentrations while diluting. Here, \( M_1 \) and \( V_1 \) are the molarity and volume of the starting solution, while \( M_2 \) and \( V_2 \) are for the final solution.
This equation allows you to calculate any unknown parameter when the others are known. It's an ideal way to scale solutions without overusing precious chemicals or creating waste.

• Always measure volumes accurately to avoid errors in dilution.
• Mix properly to ensure the solute is evenly distributed in the solution.