Titration of HCl with Sodium Hydroxide Lab Report for the Subject of Advanced Chemistry Anon Durongpisitkul, Karis Katekovit, Varun Saketharam,Thanon Thamvorapol, Chanon Anektanasup- January 28, 2017 1
Introduction Titration is a process used by chemists to determine the concentration of a particular acid or base solution. The reaction process is typically an acid reacting with a hydroxide base producing Salt and Water. A ph indicator can be used to tell us when the reaction has completely neutralized. All the acid in the reaction is consumed and there is no excess base from the reaction. This is called the equivalence point. We can use this equivalence point to determine the concentration of the acid via calculations. The goal of this experiment is to get as close as possible to the equivalence point so that our acid concentration will be as close to the true value as possible. 2
Instructions 1. Record the molarity of the sodium hydroxide solution on the data sheet 2. Obtain about 100 ml of the Sodium Hydroxide solution in a clean beaker. This should be enough for the initial cleaning of your buret and for your first 3 trials. 3. Clean your buret: Add about 5 ml of the base solution from the beaker to the buret (use a funnel to pour). Move the funnel around while adding to ensure the sides of the buret are coated with base. Alternatively, you can remove the buret with the 5 ml of titrant form the buret stand and carefully tilt and rotate to coat all interior surfaces with the titrant. Drain the solution through the stopcock into a waste beaker. Repeat this rinse with a second 5 ml portion of the base. 4. Pour more of the sodium hydroxide solution into the buret until it is near the 0.00 ml mark. Open the stopcock to allow several drops to rinse through the tip of the buret. This should eliminate any air bubbles in the buret tip. Record your initial buret reading on the data sheet for trial 1 (the volume does not need to be exactly 0.00 ml). 5. Draw 10 ml of the acid solution into the volumetric pipet and transfer this solution into an Erlenmeyer flask. Add 2-3 drops of phenolphthalein to the acid solution in the flask. 6. Place the flask under the buret and start adding the base solution the the flask. One person must continually swirl the flask while the other person controls the stopcock. Slow down once the solution starts to turn pink. Add one drop at a time until a light pink color stays for 30 seconds. 7. Record and wash the flask. 8. Repeat until you get less than 1.0% difference. 3
Discussion 1. Why did the solution turn out as different shades of pink? The reason was most likely due to the amount of base added during the titration. More base meant a darker pink solution. Frankly speaking, it was due to the imprecise nature of experiments. 4
Post-lab Questions 1. How would it affect your results if you used a beaker with residual water in it to measure out your standardized sodium hydroxide solution? The HCl will be used more than normal because the water will already partially neutralize the acid (decreasing the M). Thus the molar of the acid will be greater than actual value. 2. How would it affect you results if you used a wet Erlenmeyer flask instead of a dry one when transferring your acid solution from the volumetric pipette? The NaOH will be used less than normal because the water will already partially neutralize the acid (decreasing the M). Thus the molar of the acid will be less than actual value. 3. How do you tell if you have exceeded the equivalence point in your titration? When the solution stops changing the color it means that the solution has gone pass the indicator range (which is too basic to be equivalent) 4. Vinegar is a solution of acetic acid (CH3COOH) in water. For quality control purposes, it can be titrated using a sodium hydroxide to assure a specific % composition. If 25.00 ml of acetic acid is titrated with 9.08 ml of a standardized 2.293 M sodium hydroxide solution, what is the molarity of the vinegar? Molarity = Moles/Volume of solution. Moles = Molarity x Volume of solution Moles = 2.293 Moles/L x 0.00908 L =0.0208 Moles NaOH All In Moles Molarity = Moles/ Volume of solution Molarity of CH3COOH = 0.0208 Mol CH3COOH/0.02500 L = 0.8328 M of Vinegar 5
Conclusion 10 ml of a 0.09 M concentration HCL is able to titrate 9 ml of a 1 M NaOH solution 6
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