Problem 91 - Chemistry An Atoms First Approach

Question

You wish to prepare 1 L of a \(0.02-M\) potassium iodate solution. You require that the final concentration be within \(1 \%\) of \(0.02 M\) and that the concentration must be known accurately to the fourth decimal place. How would you prepare this solution? Specify the glassware you would use, the accuracy needed for the balance, and the ranges of acceptable masses of \(\mathrm{KIO}_{3}\) that can be used.

Step-by-Step Solution

Answer

To prepare 1 L of a 0.02-M potassium iodate solution within 1% of the target concentration and known accurately to the fourth decimal place, weigh out between 4.2452 g and 4.3148 g of KIO3 using a high precision analytical balance with at least 0.0001 g readability. Transfer the KIO3 to a 1 L Class A volumetric flask, dissolve it in approximately 800 mL of distilled water, and fill up to the 1 L mark with distilled water. Stopper the flask and mix well to ensure a homogeneous solution.

Step 1: Calculate the mass of potassium iodate (KIO3) required

To calculate the mass of potassium iodate needed, we can use the formula: mass = volume × molarity × molar mass where volume = 1 L, molarity = 0.02 M, and molar mass of KIO3 = 39.10 (K) + 126.90 (I) + 48.00 (O3) = 214.00 g/mol. mass = \(1 \times 0.02 \times 214.00\) g mass = 4.28 g

Step 2: Determine the acceptable mass range of KIO3

The final concentration should be within 1% of 0.02 M. So the range of acceptable molarities is: Min. molarity = 0.02 M × (1 - 0.01) = 0.0198 M Max. molarity = 0.02 M × (1 + 0.01) = 0.0202 M Convert the acceptable molarities to mass: Min. mass = \(1 \times 0.0198 \times 214.00\) g = 4.2452 g Max. mass = \(1 \times 0.0202 \times 214.00\) g = 4.3148 g The mass of KIO3 should be within the range of 4.2452 g to 4.3148 g.

Step 3: Choose the appropriate glassware and balance

To know the concentration accurately up to the fourth decimal place, we need a balance with at least 0.0001 g readability and accuracy. A high precision analytical balance would be suitable for this task. For glassware, use a volumetric flask to prepare the 1 L solution accurately. A 1 L volumetric flask with a high-quality Class A or equivalent certification would be appropriate, ensuring the final volume is within the specified error range.

Step 4: Prepare the solution

1. Weigh out the required amount of KIO3 (between 4.2452 g and 4.3148 g) on the high precision analytical balance. 2. Transfer the KIO3 to the 1 L volumetric flask. 3. Add approximately 800 mL of distilled water to the flask, ensuring all the KIO3 dissolves. 4. Fill the volumetric flask up to the 1 L mark with distilled water. 5. Stopper the flask and mix well to ensure a homogeneous solution. The 1 L of 0.02 M potassium iodate solution is now prepared with the concentration within 1% of the target concentration and known accurately to the fourth decimal place.

Key Concepts

Molarity Calculation

To prepare a precise solution, understanding molarity is essential. Molarity ( M ) is a way to express the concentration of a solution, calculated as moles of solute per liter of solution. In this exercise, we need to prepare a 1 L solution with a molarity of 0.02 M.
To find the amount of potassium iodate (KIO3) needed, you use the formula:

• mass = volume × molarity × molar mass

Given that 1 L of solution is desired and the molarity is 0.02 M, you multiply by the molar mass of KIO3, which is 214 g/mol.
This calculation results in needing 4.28 grams of KIO3. However, to ensure the concentration stays within 1% of 0.02 M, acceptable mass ranges from 4.2452 g to 4.3148 g.
Using the correct mass ensures the correct final concentration.

Analytical Balance

An analytical balance is crucial when measuring precise quantities of a substance in a laboratory setting. For this potassium iodate solution, accuracy is important, as the concentration needs to be precise to the fourth decimal place. An analytical balance offers precision and accuracy, typically with readability of 0.0001 g.
This accuracy allows the scientist to confidently measure the KIO3 mass within the very tight range of 4.2452 g to 4.3148 g.
Its stability and sensitivity make the analytical balance indispensable for creating precise and consistent solutions, ensuring high scientific standards are maintained.

Volumetric Flask

The volumetric flask is a piece of lab equipment designed for the accurate preparation of solutions. It allows for diluting a chemical to an exact volume. In this experiment, a 1 L volumetric flask is the best choice to ensure the final solution has the precise concentration of 0.02 M.
A high-quality, Class A volumetric flask is recommended for its low tolerance for error. By bringing the solution exactly to the 1 L mark after dissolving the potassium iodate, we can be sure of achieving the desired molarity.
This tool ensures the reproducibility and accuracy of the solution preparation, critical for experimental validity.

Potassium Iodate

Potassium iodate ( KIO3 ) is an important compound used in analytical chemistry and various industrial applications. In solution preparation like this, it is used as a solute to form precise concentrations.
Knowing the molar mass of potassium iodate, which is 214 g/mol, is vital as it helps in calculating the precise amount needed using molarity formula.
Its role is crucial when preparing solutions that require a specific concentration, such as medicinal or experimental solutions.
Handling potassium iodate with accuracy ensures the prepared solution meets predetermined specifications, thereby enabling reliable results during experiments.