AP Chem Unit 5: Preparing Solutions

Preparing Solutions

Importance of Preparing Solutions

• Correctly preparing solutions is a crucial skill for laboratory scientists.

• Proper concentration of solutions ensures accurate calculations and conclusions in laboratory settings.

Glassware Used in Preparing Solutions

• The primary glassware for solution preparation is the volumetric flask.

Volumetric Flask

• Function: Designed specifically to measure a precise volume of liquid.

• Design Feature: Contains a unique line on the neck indicating the specific volume to which the liquid must be filled.

Preparing a 0.15 M Solution of AgNO3

Required Steps

1. Determine Mass of AgNO3 Needed: Calculate the mass required for the desired molarity.

2. Measure Solid AgNO3: Weigh out 12.7 g of solid AgNO3.

3. Transfer to Flask: Place the measured AgNO3 into a 500 mL volumetric flask.

4. Add Distilled Water: Gradually add distilled water, shaking the flask gently until the solution reaches the line on the flask.

Preparing a 1.25 M Solution of NaCl

Overview

• This involves the dilution of a more concentrated solution.

Dilution Process

1. Understanding Changes: When water is added to an aqueous solution:

   • Volume (V): Increases.

   • Molarity (M): Decreases.

   • Moles of solute (n): Remains constant.

2. Dilution Equation: Use the equation M1V1 = M2V2 to relate the concentrations and volumes before and after dilution.

Steps to Prepare a 200 mL of 1.25 M NaCl from 4.00 M NaCl

1. Calculate Volume Needed: Determine how much of the 4.00 M solution is required.

2. Measure Volume: Use a graduated cylinder to measure out 62.5 mL of the 4.00 M NaCl solution.

3. Transfer to Flask: Add this volume to a 200 mL volumetric flask.

4. Add Distilled Water: Fill the flask with distilled water, shaking gently until reaching the line on the flask.

General Guidelines

• Specify the exact glassware and amounts of chemicals in all preparations.

• Show all calculations clearly to ensure accuracy and completeness.