Chemistry Solutions Preparation

Study Notes

Preparing Solutions

Preparing solutions is a fundamental skill in chemistry involving the accurate measurement and mixing of solutes and solvents.
A solution is a homogenous mixture of solute and solvent.
The concentration of a solution is determined by the specific amount of solute in a specific amount of solution.

Steps for Preparing Solutions

Calculations:
- Determine the desired concentration and volume of the solution.
- Calculate the amount of solute needed.
- Calculate the volume of solvent needed.
Preparation:
- Weigh the solid or measure the liquid solute.
- Dissolve or mix the solute with the solvent.

Basic Concepts

Molarity (M): Molarity is defined as the number of moles of solute per liter of solution.
- Formula: M = n ÷ V
Percent Solutions:
- Mass percent: grams of solute per 100 grams of solution.
- Volume percent: milliliters of solute per 100 mL of solution.
- Mass/Volume percent (w/v%): grams of solute per 100 mL of solution.
Dilution:
- The process of adding more solvent to a solution, increasing volume while keeping the number of moles of solute constant.
- Formula: M1V1 = M2V2
  - M1, V1: Molarity and volume of the concentrated solution.
  - M2, V2: Molarity and volume of the diluted solution.

Examples

Preparing a 500 mL solution of NaCl 0.9% w/v:
- Calculation:
  - Mass of solute = percent x volume of solution ÷ 100
  - Mass of solute = 0.9 x 500 ÷ 100 = 4.5 grams
- Preparation:
  - Weigh 4.5 grams of NaCl.
  - Transfer to a 500 mL volumetric flask.
  - Add water to dissolve and shake to promote dissolution.
  - Add water until the volume reaches the mark on the flask.
  - Close the flask and mix thoroughly.
Preparing 2 Liters of a solution of NaOH (0.5 M):
- Calculation:
  - Mass of NaOH = M x Mwt x Volume (L)
  - Mass of NaOH = 0.5 x 40 x 2 = 40 grams
- Preparation:
  - Weigh 40 g of NaOH.
  - Transfer to a 2 L volumetric flask.
  - Add water until the volume reaches 2 L.
Preparing 800 mL (0.8 L) of a 2 M sodium chloride (NaCl) solution:
- Calculation:
  - Mass = M x Mwt x Volume (L) = 2 x 58.45 x 0.8 = 93.52 grams
- Preparation:
  - Dissolve 93.52 g of NaCl in approximately 400 mL of water.
  - Add more water until the final volume reaches 800 mL.
Preparing 100 mL (0.1 L) of a 1.0 M hydrochloric acid (HCl) from a concentrated solution (12.1 M):
- Calculation:
  - V1 = M2V2/M1 = 1 x 0.1 / 12.1 = 0.00826 L = 8.26 mL
- Preparation:
  - Add 8.26 mL of concentrated HCl to approximately 50 mL of water.
  - Dilute to a final volume of 100 mL.
Preparing a standard solution of 500 mL of Na2CO3 (0.1 M):
- Calculation: Requires 5.3 grams in 500 mL solution.
Preparing a 3500 mL solution of potassium permanganate (0.08 M):
- Calculation: Requires 44.24 grams in 3500 mL solution.