1 M NaOH Solution

How to Prepare 1 M NaOH Solution

Sodium hydroxide (NaOH), widely known as caustic soda or lye, plays a crucial role in both laboratory and industrial applications. Preparing a 1 molar 1 M NaOH solution demands careful measurement, attention to detail, and a solid understanding of safe chemical handling practices. This guide outlines a clear, step-by-step method to accurately and safely prepare a 1 M NaOH solution.

Understanding Molarity and NaOH Calculation

Before preparing the solution, it’s important to grasp the meaning of a 1 M (molar) solution. Molarity, denoted as M, refers to the number of moles of solute present in one liter of the solution.

• Molarity (M) = Moles of solute / Volume of solution in liters
• For 1 M NaOH, we need 1 mole of NaOH in 1 liter of solution.

Molecular Weight of NaOH

• Sodium (Na) = 22.99 g/mol
• Oxygen (O) = 16.00 g/mol
• Hydrogen (H) = 1.01 g/mol
• Molar mass of NaOH = 22.99 + 16.00 + 1.01 = 40.00 g/mol

Therefore, to prepare 1 liter of 1 M NaOH, you must dissolve 40.00 grams of NaOH pellets in sufficient water and make up the volume to 1 liter.

Safety Precautions When Handling NaOH

NaOH is a highly corrosive substance. Improper handling can cause severe chemical burns. We must always follow strict safety protocols:

• Wear personal protective equipment (PPE): gloves, lab coat, and safety goggles.
• Work in a well-ventilated space or utilize a fume hood for safety.
• Never add water to NaOH pellets; instead, add NaOH to water slowly to prevent exothermic reactions and splashing.
• Keep a neutralizing agent, such as vinegar (acetic acid), nearby in case of spills.

Equipment and Materials Needed

To prepare a 1 M NaOH solution, gather the following items:

• Analytical balance (precision: ±0.01 g)
• Sodium hydroxide (NaOH) pellets or flakes.
• 1-liter volumetric flask or measuring cylinder.
• Beaker (250 mL or more)
• Glass stir rod or magnetic stirrer.
• Distilled or deionized water.
• Funnel
• Lab gloves, goggles, and an apron/lab coat.

Procedure to Prepare 1 M NaOH Solution

Step 1: Weigh the NaOH Accurately

Using an analytical balance, weigh out exactly 40.00 g of sodium hydroxide pellets. Transfer the NaOH into a clean, dry beaker.

Note: Work quickly, as NaOH is hygroscopic, it absorbs moisture and carbon dioxide from the air.

Step 2: Dissolve in Distilled Water

Pour about 400–500 mL of distilled water into the beaker containing NaOH pellets. Stir continuously with a glass rod or use a magnetic stirrer.

Warning: This process is exothermic, and the solution will become hot. Allow it to cool to room temperature before proceeding to the next step.

Step 3: Transfer to Volumetric Flask

Once fully dissolved and cooled, transfer the NaOH solution into a 1-liter volumetric flask using a funnel. Ensure all the solution and any residue are rinsed from the beaker into the flask.

Step 4: Make Up the Volume

Add distilled water gradually to the volumetric flask until the bottom of the meniscus reaches the 1-liter calibration mark.

Tip: Use a dropper for the last few milliliters to ensure precision.

Step 5: Mix Thoroughly

Stopper the flask and invert several times or stir to ensure the solution is uniformly mixed.

Labeling and Storage of NaOH Solution

Once your solution is ready:

• Label the container clearly with:
  • “1 M NaOH”
  • Date of preparation
  • Your initials or laboratory designation

Store the solution in a plastic or Teflon container. Avoid glass bottles, as NaOH can slowly corrode glass, especially over long periods.

Store the container securely with the lid tightly closed, and keep it away from direct sunlight and heat sources. When properly stored, NaOH solution can remain stable for several weeks to months, depending on exposure conditions.

Important Tips for Best Results

• Always use analytical-grade NaOH for lab preparations.
• Use CO₂-free distilled water if possible to avoid the formation of sodium carbonate.
• If using flakes or pellets stored for a long time, they may already have absorbed moisture. Reweigh or standardize if necessary.
• Standardize the NaOH solution using a primary standard acid such as potassium hydrogen phthalate (KHP) if precise concentration is required for titration purposes.

How to Standardize 1 M NaOH Solution (Optional)

To verify the exact molarity, titrate with a known volume of KHP (potassium hydrogen phthalate, C₈H₅KO₄), which has a molar mass of 204.22 g/mol.

1. Accurately weigh about 0.2042 g of KHP and dissolve in distilled water.
2. Add a few drops of phenolphthalein indicator.
3. Titrate with the NaOH solution until a persistent pale pink color appears.
4. Use the volume of NaOH used to calculate its exact concentration.

Common Errors to Avoid

• Not allowing the solution to cool before dilution affects the final volume and concentration.
• Adding water to NaOH instead of the reverse is a dangerous reaction.
• Inaccurate weighing due to NaOH absorbing moisture from the air.
• Not mixing thoroughly after dilution leads to uneven concentration.

Final Thoughts

Preparing a 1 M sodium hydroxide solution is straightforward when following the right protocol. Ensuring safety, precision, and correct technique guarantees a reliable solution for laboratory and industrial use. Always handle NaOH with caution and respect, given its reactive and corrosive properties.