The MicroLAB™ Interface: Plotting Measured Data to Generate a Graph

Outline Purpose Acid-Base Reactions pH and IC probe function Waste and Solutions Following Lab Reminder

Purpose You will learn to use MicroLAB™ for data acquisition and analysis. A graphical representation of temperature and pH changes will demonstrate chemical changes related to acid-base reactions.

pH The pH scale ranges from 0 to 14. The pH of a solution tells us if that solution is acidic, basic or neutral.

Acids Acids are compounds that donate H+ to a solution. The pH of an acid always falls below 7. The stronger the acid, the closer the pH is to 0. HCl (hydrochloric acid) is considered a strong acid.

Bases Bases are compounds that donate OH- to solutions. The pH of bases always fall above 7. The stronger the base, the closer the pH is to 14. NaOH (sodium hydroxide) is considered a strong base.

Neutral Solutions Neutral Solutions have a pH of 7. These solutions are neither acidic nor basic. Water is considered “neutral.”

Acid-Base Reactions HCl(aq) + NaOH(aq) → H2O(l) + Na+(aq) + Cl-(aq) + heat A strong acid and a strong base react to produce water and a salt (neutralization). This process releases heat (exothermic reaction). We can measure the change in temperature that takes place. We can measure the pH change.

Calculations You can determine the volume of base needed to complete your reaction today by using the equation MaVa = MbVb You must know the values for the other three variables first.

Calculations Ma = 0.25* M HCl Va = 85.0 mL Mb = 0.25* M NaOH Vb = Unknown Vb = *Get the exact number from the appropriate carboy!

pH and Temperature Probes Be careful! These probes are fragile. You will use a pre-calibrated template for both the temperature and pH probes. Remember to rinse and dry the probes before each transfer. This will prevent cross-contamination. Your instructor will show you how to set up your probes and glassware.

Safety Concerns Reagents: Eye Contact: Skin Contact: Inhalation: HNO3 (1 N) / HCl (0.2 N) NaOH / KOH Eye Contact: Irritating, burns, permanent eye damage, tearing, redness, pain, impaired vision, blindness Skin Contact: Irritating, redness, pain, soreness, severe skin burns, ulcers, stains, destruction, scaling, and blistering Inhalation: Breathing difficulties, pneumonia, pulmonary edema, coughing, choking, irritation of nose, throat, and respiratory tract, burns, and death Ingestion: Pain and burns of the mouth, throat, esophagus and gastrointestinal tract. Corrosive to mucous membranes, perforation of the esophagus and stomach, abdominal pain, nausea, vomiting, abnormal sensations of hands and feet, and general gastro-intestinal upset.

Waste and Solutions Conserve distilled water during cleanup! Only neutral solutions can go down the sink after you are finished with your experiments. All solutions with a pH below 6 or above 8 should go in the acid / base waste container.

Lab 6 Reminder Do the required reading from your textbook and manual. Complete your pre-lab questions. Study for the quiz. Submit your Lab 5 Report at the start of next week’s lab.