BASE ONE LABS SKIN

You will need this sheet to record your data. Lab Procedure Please print the worksheet for this lab. Students who do not complete the WebAssign prelab are required to bring and hand in the prelab worksheet.

Check your WebAssign Account for due dates. Prior to Class Please complete WebAssign prelab assignment. When disposing of concentrated solutions, pour them slowly while the water is running. Waste Disposal All solutions can be flushed down the sink with plenty of water. Remember to wash your hands with soap and water when the experiment is completed. The chemicals used in this experiment are very dilute so gloves will not be available. Use caution when pouring solutions or disposing of them. Do not directly combine solutions with concentrations greater than 0.1 M. They can cause water to boil and splash hot, corrosive solution out of the vessel in which they were mixed. Acid-base reactions are highly exothermic. Have your lab partner notify your instructor about the accident. If you do inhale enough vapor to have a problem, move to fresh air. Work with concentrated solutions under the hood so vapors do not build up in the lab. HCl, HC 2H 3O 2 and NH 3 solutions give off highly irritating vapors. Have your lab partner notify your instructor about the spill.

BASE ONE LABS SKIN

If contact with skin or clothing occurs, flush the affected area with water. Hold your eyes open and flush with water. If any of these solutions splash into your eyes, use the eyewash immediately. They can attack the skin and cause permanent damage to the eyes. Safety HCl, NaOH, HC 2H 3O 2 and NH 3 are corrosive. In Part D, you will use a pH electrode to follow the pH change of an acidic solution as a basic solution is added to it. In Part C, you will use pH paper to determine whether several common household chemicals are acidic, basic, or neutral. In Part B, you will use pH electrodes to determine the pH of several acid-base solutions commonly found in a chemistry laboratory to become familiar with the pH scale. In Part A of this lab, you will calibrate a pH electrode and check the calibration with 3 buffer solutions. The color of the indicator changes with pH, so the approximate pH of a solution can be determined by placing a small amount of the solution on the paper. pH paper is a strip of paper with an indicator on it. When the indicator is placed in an acidic solution, it is converted to the acid form and takes that color, but when it is placed in a basic solution, it is converted to the base and takes on the color of the base.

An acid-base indicator is a weak acid whose conjugate base is a different color. The voltage is converted to a pH that can be read directly. When the electrode is placed in a solution, a voltage is developed between the electrode and the solution. pH electrodes are electrochemical cells whose voltage is pH sensitive. The acidity or basicity of a solution can be determined by measuring its pH or with an indicator. The general form of the acid dissociation reaction and K a are shown below in equation 1. The larger the K a, the stronger the acid is. This equilibrium constant is defined as the acid dissociation constant or K a of the acid. The greater the extent of this reaction, the larger the equilibrium constant is for the reaction. The acidity of a Brønsted acid is a measure of the extent to which the acid reacts with the weak base H 2O to produce its conjugate base and H 3O + ions, the conjugate acid of water. Brønsted acid-base reactions contain two conjugate acid-base pairs and nothing else. The conjugate acid of a base is obtained by adding one H + to the base, so the conjugate acid of CN – is HCN. Thus, the conjugate base of an acid is obtained by removing one H +, so the conjugate base of HF is the F – ion. Conjugate acid-base pairs differ by exactly one proton. A Brønsted acid-base reaction is the transfer of a proton from the acid to the base to form their conjugate acid-base pairs. NH 3 is the most common base that is not an anion. Protons have positive charge, so their acceptors usually have negative charge, i.e., most anions are bases. Although it contains four protons, only one is acidic. For example, acetic acid has the formula HC 2H 3O 2. In this theory, an acid is a proton (H +) donor and acids can usually be recognized because protons that can be transferred are written first in the chemical formula. There are three definitions used to describe acids and bases, but we consider only the Brønsted definition here. Introduction Many substances can be classified as acids or bases. 3 To observe pH changes produced upon addition of acid or base to a solution.

Base one labs