How to Prepare a 1.25 m Molality Sucrose Solution: A Comprehensive Guide

Biochemistry and chemistry students, as well as those working in pharmaceuticals and chemical industries, sometimes need to prepare specific solutions for various experiments and applications. One common task is to prepare a 1.25 m molality solution of sucrose. This guide will walk you through the precise steps needed to dissolve 50.0g of sucrose (C12H22O11) in water, resulting in a 1.25 m molality solution.

Understanding Molality

Molality is a measure of the concentration of a solute in a solution. It is defined as the number of moles of solute per kilogram of solvent. In this case, we want to dissolve 50.0g of sucrose in water to achieve a 1.25 molality (m) solution. Let's break down the process step by step.

Step 1: Calculate the Molar Mass of Sucrose

First, let's determine the molar mass of sucrose (C12H22O11). The molar mass of sucrose can be calculated by adding the atomic masses of all its constituent atoms:

Carbon (C): 12 atoms × 12.01 g/mol 144.12 g/mol Hydrogen (H): 22 atoms × 1.01 g/mol 22.22 g/mol Oxygen (O): 11 atoms × 16.00 g/mol 176.00 g/mol

Therefore, the molar mass of sucrose is:

Molar mass of sucrose 144.12 22.22 176.00 342.34 g/mol

Step 2: Determine the Moles of Sucrose

To find how many moles of sucrose we have, we divide the given mass by the molar mass:

N1 (moles of sucrose) 50.0 g / 342.34 g/mol 0.146 moles

Step 3: Calculate the Required Volume of Water

Now, we need to calculate how much water in kilograms is required for a 1.25 m molality solution. Molality is defined as:

molality (m) moles of solute / mass of solvent (in kg)

Given that we have 0.146 moles of sucrose and we want a 1.25 m molality solution, we can set up the following equation:

1.25 m 0.146 moles / x kg

Solving for x, the mass of water in kg:

x kg 0.146 moles / 1.25 m 0.117 kg

Since water's density is approximately 1 g/mL or 1000 g/L, the required volume of water is:

Volume of water 0.117 kg × 1000 g/kg 117 g 117 mL

Step 4: Dissolve Sucrose in Water

To prepare a 1.25 m molality sucrose solution, measure 117 g of water and bring it to a suitable container. Slowly add 50.0 g of sucrose to it and dissolve it completely. Stir gently to ensure all sucrose is dissolved.

Conclusion

By following these steps, you will have successfully prepared a 1.25 m molality sucrose solution. This process involves calculating the molar mass of the solute, determining the moles of solute, and then calculating the required volume of solvent to achieve the desired molality. Whether you are a student, a researcher, or an industrial chemist, understanding and being able to prepare solutions accurately is an essential skill. Remember, the precision in preparing solutions is critical for reliable and reproducible results in all scientific experiments.

Keywords: molarity, molality, sucrose, dissolved mass, solvent