A chemical solution is a homogeneous mixture where a solute is uniformly dispersed throughout a solvent. Preparing solutions of a precise strength is a frequent requirement in nearly every scientific laboratory. The concentration of a solution is quantitatively expressed in several ways, with Molarity (M) being the most common unit in chemistry. Molarity is defined as the number of moles of solute dissolved per liter of the total solution volume.
Calculating the Required Mass of Solute
The preparation of a 1M solution begins with a calculation converting the required number of moles into a measurable mass in grams. Molarity is expressed as moles per liter. Since the goal is typically to create one liter of a 1M solution, the calculation focuses on finding the mass equivalent of one mole of the solute.
This conversion uses the solute’s Molar Mass (MM), which is the mass of one mole of a substance expressed in grams per mole (g/mol). The general formula applied is: \(\text{Mass required (g)} = \text{Molarity (M)} \times \text{Volume (L)} \times \text{Molar Mass (g/mol)}\). For example, preparing one liter of a 1M sodium chloride (NaCl) solution (MM of \(58.44\text{ g/mol}\)) requires \(1\text{ M} \times 1\text{ L} \times 58.44\text{ g/mol}\), which equals \(58.44\text{ grams}\) of NaCl.
Necessary Laboratory Equipment
Accurate preparation of a 1M solution requires specialized, high-precision laboratory equipment.
- An analytical balance is used to weigh the solute to an accuracy of at least \(0.0001\text{ grams}\). This precision is necessary because the calculated mass determines the final concentration.
- The volumetric flask is a container with a single calibration mark, calibrated to contain one exact volume, making it indispensable for standardized solutions.
- A powder funnel is required to ensure the quantitative transfer of the weighed solute into the narrow neck of the flask without loss.
- A stirring rod or magnetic stirrer is needed to ensure the solute dissolves completely and the mixture is fully homogeneous before the final volume adjustment.
Preparing the 1M Solution
Preparation begins after the calculated mass of the solute is accurately weighed. The entire measured mass is carefully transferred into the volumetric flask using a clean powder funnel. It is good practice to rinse the weighing container and the funnel multiple times with a small amount of solvent (typically distilled or deionized water) to ensure a complete transfer of the solute.
The solute must be completely dissolved before the final volume is reached. A small amount of solvent, usually filling the flask about one-third to one-half full, is added next. The flask is then swirled or gently agitated until the solid is no longer visible, confirming the solute is fully in solution. It is important to wait until the solution reaches room temperature if the dissolution process caused any heating, as volume changes with temperature.
More solvent is then added until the liquid level is just below the calibration mark on the neck of the flask. The final step involves adding the last few drops of solvent using a dropper or wash bottle until the bottom of the meniscus aligns exactly with the calibration line. The flask is then sealed with a stopper and inverted and swirled repeatedly to ensure the resulting 1M solution is thoroughly mixed and homogeneous.