Question

Give precise instructions to your laboratory assistant as to how to prepare \(1.00 \mathrm{~L}\) of a \(1.00 \mathrm{M}\) aqueous solution of sucrose, \(\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}\). Remember that she will be measuring out the sucrose in grams. She has available a 1-L volumetric flask.

Short answer

First, calculate the molecular weight of sucrose, C12H22O11, which is 342.34 g/mol. To prepare a 1.00 L, 1.00 M solution, you'll need to weigh out 342.34 grams of sucrose. Transfer the sucrose to a 1-L volumetric flask and fill it halfway with distilled water. Stir using a glass rod until sucrose is completely dissolved. Slowly add water until the meniscus reaches the 1-L mark. Attach the stopper and gently mix the solution by inverting it multiple times.

Step-by-step solution

Calculate the molecular weight of sucrose (C12H22O11)

First, we need to find the molecular weight of sucrose. This can be found by multiplying the number of atoms of each element by their respective molar masses and then adding the products together: Molecular weight of sucrose = (12 * \(C\)) + (22 * \(H\)) + (11 * \(O\)), where \(C\), \(H\), and \(O\) are the molar masses of carbon, hydrogen, and oxygen, respectively. Using the molar masses: \(C = 12.01 \mathrm{~g/mol}\), \(H = 1.01 \mathrm{~g/mol}\), and \(O = 16.00 \mathrm{~g/mol}\), we have: Molecular weight of sucrose = (12 * 12.01) + (22 * 1.01) + (11 * 16.00) = 144.12 + 22.22 + 176.00 = 342.34 g/mol.

Convert molarity to mass of sucrose required

We're asked to prepare a 1.00 L aqueous solution of sucrose with a concentration of 1.00 M. To find how many grams of sucrose are needed for this, we use the formula: Mass of sucrose = Molarity * Molecular weight * Volume of solution Plug in the values: 1.00 M * 342.34 g/mol * 1.00 L = 342.34 g So, 342.34 grams of sucrose is required.

Prepare the 1.00 L solution of sucrose in the 1-L volumetric flask

Follow these steps to prepare the solution: 1. Weigh 342.34 grams of sucrose using an electronic balance and transfer it to the 1-L volumetric flask. Do this carefully to ensure that all sucrose is transferred to the flask. 2. Add distilled water to the sucrose-containing flask, filling it approximately halfway. 3. Use a glass stirring rod to stir the contents of the flask until the sucrose is completely dissolved in the water. This may take a few minutes. 4. Once the sucrose has dissolved, slowly add distilled water to the flask until the meniscus reaches the 1-L mark on the flask. Be careful not to add too much water, as the meniscus should just touch the 1-L mark. 5. Attach the flask's stopper, and mix the solution gently by inverting the flask several times. Be sure to hold the stopper in place to prevent spills. Now, the 1.00 L of a 1.00 M aqueous solution of sucrose is prepared, and the laboratory assistant should store the volumetric flask in a safe and appropriate location until it is needed for further use.

Key concepts

Understanding Molarity

Molarity is a fundamental concept in chemistry, especially when preparing solutions in the laboratory. It expresses the concentration of a solution. Specifically, it measures the number of moles of solute—such as sucrose —dissolved in one liter of solution.
To calculate molarity, you use the formula:

• Molarity (M) = Moles of solute / Liters of solution

In our exercise, we aimed for a 1.00 M solution of sucrose, which means each liter of solution should contain 1 mole of sucrose.
It's important to always check the desired molarity when preparing solutions so that you can precisely measure the needed amount of solute.

Calculating Molecular Weight

Molecular weight is essential for determining how much of a chemical you need. It represents the mass of one mole of a substance, usually expressed in grams per mole (g/mol).
To find the molecular weight of sucrose (C\(_{12}\)H\(_{22}\)O\(_{11}\)), you'd multiply the number of each type of atom by its atomic mass and then sum these values:

• For Carbon: 12 atoms x 12.01 g/mol = 144.12 g/mol
• For Hydrogen: 22 atoms x 1.01 g/mol = 22.22 g/mol
• For Oxygen: 11 atoms x 16.00 g/mol = 176.00 g/mol

Adding these gives a molecular weight of 342.34 g/mol for sucrose. Knowing this allows us to convert between moles and grams easily, which is crucial for solution preparation.

Key Laboratory Procedures

Proper laboratory procedures are critical for preparing chemical solutions. When making a solution like sucrose in our exercise, follow these key steps:

• Weigh the precise amount of the substance using a balance to ensure accuracy.
• Use clean equipment to avoid contamination.
• Initially add only part of the solvent to dissolve the solute efficiently.
• Stir using appropriate tools, such as a glass rod, to aid dissolution.
• Fill to the final desired volume carefully to ensure correct concentration.
• Mix thoroughly to ensure even distribution of solute within the solvent.

Adhering to these procedures ensures consistency and reliability in experiments, leading to accurate results.

Volumetric Flask Usage

A volumetric flask is an essential tool for preparing precise solution concentrations. It's designed to allow for accurate measurement of liquids. Here are some tips for using a volumetric flask effectively:

• Make sure the flask is clean and dry before use to prevent contamination.
• Transfer the solute without spilling to maintain accuracy.
• Initial filling should be partial to help dissolve the solute.
• Use the meniscus—a curve seen at the liquid's surface—to measure the precise volume.
• Look at the meniscus at eye level to avoid parallax error, a common mistake in volume measurement.
• Mix the solution thoroughly by inverting the flask gently.

Proper use of a volumetric flask ensures that your solution is both precise and ready for use in further experiments.