EXERCISE 4: pH, ACIDS, BASES, AND BUFFERS Lab 2_DL Week#2 • MICROSCOPE • pH, ACIDS, BASES, AND BUFFERS TODAY The compound microscope The compound microscope OCULAR LENS (eyepiece) – Your microscope...

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EXERCISE 4: pH, ACIDS, BASES, AND BUFFERS Lab 2_DL Week#2 • MICROSCOPE • pH, ACIDS, BASES, AND BUFFERS TODAY The compound microscope The compound microscope OCULAR LENS (eyepiece) – Your microscope have two (binocular) ocular lenses. These are the lenses you will look through when examining a specimen with the microscope. Each ocular lens magnifies the image by a factor of 10 or 10X. OBJECTIVE LENSES – The set of objective lenses are on the revolving nosepiece. These lenses allow you to change the degree of magnification. Our microscopes have four objective lenses. The degree of magnification for each objective lens is indicated on its side. 5X – This objective magnifies the image by a factor of 5. It is referred to as the “scanning objective” since it is used to scan the slide to locate the specimen before viewing it at higher magnification. 10X – This objective magnifies the image by a factor of 10 and is referred to as the “low power” objective. 40X – This objective magnifies the image by a factor of 40 and is referred to as the “high power” objective. 100X – This objective magnifies the image by a factor of 100. It is referred to as the “oil immersion objective” since it requires a drop of immersion oil on the slide to provide good resolution. Lenses of the compound microscope The total magnification of an image is the product of the ocular lens magnification times the magnification of the objective lens you are using. Magnification of ocular x magnification of objective = total magnification For example, if the ocular lens magnifies the image by a factor of 10 (10X), and the objective lens magnifies the image by a factor of 40 (40X), the total magnification of the image is 400X. (10X x 40X = 400X) Total Magnification Field of View The Field of View decreases when the magnification increases The field of view (FOV) is the actual “circle” you see when looking in the microscope. Although this circular field of view appears to be the same no matter which objective lens you are using, this is not the case. The circular area you are actually viewing will decrease as you increase the magnification. The field of view Objectives • Once you have a specimen in focus under the microscope, if you adjust the fine focus knob up and down the specimen will come in and out of focus. Thus, there is a range in the vertical dimension in which the specimen on your slide will appear in focus. • The “thickness” of the vertical range in which the specimen remains in focus is referred to as the depth of focus. • The depth of focus decreases as the magnification increases Depth of focus depth of focus Depth of focus Video of depth of focus https://youtu.be/kJZh9wY37UM Low magnification high magnification The depth of focus decreases as the magnification increases https://youtu.be/kJZh9wY37UM https://youtu.be/kJZh9wY37UM 1. Place a drop of Water on the clean Slide 2. Place Specimen in a drop of water 3. Place one edge of cover glass against the slide so that cover glass touches the water drop 4. Lower cover glass gently onto the slide. Preparation of a wet-mount slide Acids, Bases and pH (Ex 4) An acid is a substance that increases the concentration of hydrogen ion (H+) HCl à H+ + Cl- A base is a substance that decreases the concentration of hydrogen ion (H+) Hydrochloric acid (hydrogen chloride) Hydrogen ion chlorine NH3 + H+ à NH4+ Ammonia Hydrogen ion Ammonium ion (cation) NaOH à Na+ + OH- OH- + H+ à H2O Sodium hydroxide Sodium Hydroxide ion Hydrogen ion water pH scale indicate the strength of acids and bases • The pH is a measure of the hydrogen ion concentration in a solution o pH = -log [H+] o [H+] = 10 -pH • pH scale ranges from 0 to 14 • Acids have a pH less than 7 • Bases have a pH greater than 7 • Pure water has a pH of 7 Lab manual p41 Activity I: Determining pH of Different Solutions 2 4 13 11 6 3 4 6 5 3 2 11 acidic acidic basic basic acidic acidic acidic acidic acidic acidic acidic basic David • A Buffer is a compound or a combination of compounds that can combine with or release hydrogen ions to keep the pH of a solution relatively constant. • A buffer solution resists changes in pH when small quantities of an acid or an alkali are added to it Buffer CH3COOH(aq) CH3COOH- + H+ Ethanoic acid Hydrogen ion Ethanoate CH3COOH(aq) CH3COOH- + H+If acid added CH3COOH(aq) + OH- CH3COOH- + H2OIf base added • Organisms control the pH of cellular and body fluids by using buffers. e.g. Blood as a pH of 7.4 and serves also has a buffer Buffer Lab manual p41 Activity II: The Action of a Buffer water buffer water buffer Place 50 ml of pure water Place 50 ml of buffer water buffer Place 50 ml of pure water Place 50 ml of buffer Measure the pH of each beaker Add 1 mL of 0.1N HCl then measure the pH of each beaker. Repeat 4 times Lab manual p42 Activity II: The Action of a Buffer 7 7 6.5 7 6.5 7 7 6 5.5 4 3.5 3