Intro: Simple Strong Acid and Base Titration
A titration is a process that allows the equilibrium ratios, or equivalent amounts, of chemicals to be observed through a change in color. The characteristic indicator that a solution has reached equilibrium is a color change which is brought on by a change in pH. A chemical, or pH indicator, is chosen based off of the calculated equilibrium pH. The pH indicator will change color in that range to signify the equilibrium has been attained. The pH range measures how close or far away from neutral the solution is. Water, for example, has a pH of 7.0 and is considered 'neutral'. From 0.0<7.0, the solution is acidic, and from 7.0<14.0, the solution is considered basic. In an analysis of a strong base and a strong acid, a perfect balance of these two should produce a perfectly neutral solution since the ions of the separate solutions will dissolve equally creating a balance of positive and negative charges of atoms.
This instuctrable will lay out the process for creating two stock solutions of a strong acid and base for testing from lab worthy chemicals, how to set up the titration apparatus, and preforming the actual experiment. The stock solutions are sodium hydroxide, a strong base, or hydrochloric acid, a strong acid. An indicator is a certain chemical that changes color depending on the pH, the acidity or basicity, of a liquid mixture. Any sort of chemical experiment involving bases and acids especially requires care not to injure oneself, so wearing a lab coat, goggles and proper attire will help in case of a tragic accident. A laboratory is the ideal place for experiments.
- 2 50 mL Beakers
- 50 mL Burette
- 1.0 M HCl (hydrochloric acid)
- 1.0 M NaOH (sodium hydroxide)
- 100 mL Graduated Cylinder
- Lab Coat
Time and Cost
One hour is a decent approximation for a beginner performing this elementary titration. A reasonable price for the sodium hydroxide and hydrochloric acid stock solutions are $45.00 if purchased as 1 liter amounts and in a concentration of 1M from a chemical supplier. Phenolphthalein cost $5.00 for a modicum but effective amount (only two drops are needed). An expected budget for glassware is $40.00, and the personal protective equipment will cost around $12.00. (Total price: ~$102.00)
As briefly mentioned, this instructable does deal with dangerous acids and bases. Drinking the chemicals, splashing them on oneself, or doing anything questionable is potentially harmful. Before dealing with these chemicals, search the material safety data sheet (MSDS) information online. Pouring acid into water could cause explosive release of heat, so always pour the acidic solution into a more basic one. Phenolphthalein is a dye and will stain clothes. Broken glass is always a hazard since accidents do happen. having baking soda nearby to neutralize any acid spill is always a good fail-safe.
Step 1: Preparation
- Put on your gloves, eye-wear, and other protective gear before you begin.
- Make sure all your glassware is cleaned with water and dried with a paper towel.
- Label your two beakers clearly "solution" and "base".
- Set-up the burette on a stand by attaching it with a clip (The stopcock should have instructions with the kit).
- Make sure that the stopcock's dial is horizontal.
Step 2: Measuring Out the Chemicals
- Pour from the stock HCl bottle and fill the clean graduated cylinder to the 20 mL mark.
- Transfer the amount into the "solution" beaker.
- Clean the graduated cylinder with plenty of water.
- Pour the NaOH stock solution into the graduated cylinder to the 30 mL mark (note* if the glassware is unclean, it could ruin the experiment!).
- Carefully pour the 30 mL into the burette (the burrette measures from top to bottom, so it should indicate 20 mL).
Step 3: Add the Indicator
- Drip two-four drops of phenolphthalein into the "solution" container (it will still be clear).
- Place the "solution" beaker underneath the burette carefully.
Step 4: Doing the Titration
- (Optional) To improve the visibility, place the "solution" on a white surface such as a piece of paper
- Turn the stopcock vertically to allow the sodium hydroxide to fill into the "solution" beaker (there should be a pink color where the base goes in)
- Let the fluid go out in a steady stream until the fluid level reaches 35 mL.
- At this point, slow the stream down to a drop-by-drop speed (the solution will remain pink when it is complete).
- At 38 mL, monitor each drop and stir the beaker a little to see if a slight pink color stays in the solution or dissipates to colorless (A darker pink color means that the solution is saturated beyond the point of equilibrium).
- Take note of the last fluid level the burette read (it should be around 40 mL).
Step 5: Clean-Up
- Now that you have a pink solution, allow for the rest of the NaOH to flow into the the beaker.
- Pour ~10 mL (fill up the beaker) with water, then pour the "solution" down the drain.
- Clean all glassware with water(burette, beakers, graduated cylinders).
- Store the stock chemicals in a safe, designated area.
Now that you have done the titration, the end result should have been at 40 mL (20 mL of acid: 20 mL of base). If it was not exactly that amount, there is no need to worry. Titrations at this level have a limit to the ability for accuracy from your eyesight and perception of the endpoint, measuring inaccuracy of instruments and any other random factor. This is an integral chemical process and when used by large corporations, digital equipment vastly increases the accuracy of measurements.
I hope that this instructable was pleasing and straight-forward. If you have any comments, suggestions or questions, please leave a message below and I will acknowledge your feedback any way that I can. I appreciate your support and your enthusiasm for science!