Piedmont Hills High School – AP Chemistry 2017-2018 Phan, Madalyn Period ⅘ Laboratory Experiment 3 : Titration Lab PURPOSE: Determine the concentration of an unknown HCl solution through the titration of our NaOH solution from task 2. INTRODUCTION: To complete this task, we must familiarize ourselves with the buret. The buret is a long volumetric glassware used to deliver variable liquid amounts typically for titrations. On one end, it is open for filling, the other end has a stopcock that is used to control the flow of the liquid. The keen control helps achieve the exact amount of titrant needed to neutralize the titrand. They typically hold 50 mL of liquid and experimenters must read the buret at eye level and at the lowest meniscus to conclude how many milliliters of titrant were used to reach the endpoint, the point when enough titrant has been added to the titrand and indicator to facilitate a color change. Speaking of titrand and titrant, titrant is the solution inside the buret and titrand is the solution that the titrant is being dropped into. Another device that needs to be known is the magnetic stir plate and stirrer; these help with mixing the titrand while the titrant is being dripped into it. As for calculations, an important formula is the molarity formula, listed below, which helps solve for the concentration of solutions. Additionally, another important aspect that should be acknowledged is the indicator. Indicators are substances whose solutions change color due to changes in pH, which will assist experimenters in determining when the titrand has been neutralized. In this case, the color pink will indicate that the titrand has been standardized. Lastly, we performed an experiment prior to
this lab, titled “Task 2,” to find the concentration of the NaOH we used in this lab. Here are the computations from that experiment: Trial 1: 0.795 g KHC 8 H 4 O 4 x (1 mole KHC 8 H 4 O 4 / 204.213 g KHC 8 H 4 O 4 ) x (1 mole NaOH / 1 mole KHC 8 H 4 O 4 ) = 0.00389 mole NaOH M = 0.00389 mole NaOH / 0.0185 L = 0.210 M Trial 2: 0.503 g KHC 8 H 4 O 4 x (1 mole KHC 8 H 4 O 4 / 204.213 g KHC 8 H 4 O 4 ) x (1 mole NaOH / 1 mole KHC 8 H 4 O 4 ) = 0.00246 mole NaOH M = 0.00246 mole NaOH / 0.0116 L = 0.212 M Trial 3: 1.000 g KHC 8 H 4 O 4 x (1 mole KHC 8 H 4 O 4 / 204.213 g KHC 8 H 4 O 4 ) x (1 mole NaOH / 1 mole KHC 8 H 4 O 4 ) = 0.00490 mole NaOH M = 0.00490 mole NaOH / 0.0218 L = 0.225 M Average Concentration: (0.210 + 0.212 + 0.225) / 3 = 0.216 M MATERIALS: ● Unknown concentration of HCl solution ● 0.216 M of NaOH ● Distilled water ● Buret clamp ● Buret ● Ring stand ● Phenolphthalein Indicator ● Squirt bottle ● Erlenmeyer Flask (200 mL) ● Magnetic stir plate ● Magnetic stirrer ● Graduated cylinder (10ml, 25ml) ● Beaker (250ml, 250ml, 100ml, 150ml) METHODOLOGY: Step 1: Titration of HCl 1. The buret was filled with NaOH to or past the zero ml mark 2. The stopcock was turned so that the bottom of the buret could fill with NaOH and the volume would be at the zero mL mark (or at a mark around there because it was hard to get the volume at exactly at 0 mL)
3. 16 mL of the HCl solution was collected in a 50mL graduated cylinder 4.
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