ScholAR Chemistry has provided a useful reference guide for school laboratories. Information in the guide includes:
- cleaning and sterilizing glassware
- cleaning microscopes
- pH Defined
- making a buffering solution
- preparing molar & normal solutions
- dilution table for liquids
- useful reagents
- common preservatives and fixatives
- general stains
- Centigrade - Fahrenheit conversions
- Mohs’ Scale of Hardness
- weight, length and volume conversions
- table of atomic symbols, numbers and weights
Most of the reference material is included below for quick, easy access. However, conversion charts and other large tables are available in the PDF file linked below:
Ward’s ScholAR Lab Reference Guide (PDF, 60 kb)
Cleaning Glassware
- Add Alconox detergent to water. Stir into solution.
- Soak glassware in solution, then clean using a brush or scouring pad.
- Rinse well in tap or distilled water.
Sterilizing Glassware
- Using an oven: Place in an oven and heat at 160-190°C (320-374°F) for at least one hour. Note that paper and cotton char at 175°C (about 350°F). If glassware is packed in metal containers for sterlizing, heat for at least two hours.
- Using an autoclave: Place glassware in autoclave or pressure cooker. Close the lid. Make sure to open the safety valve to allow all the air to escape before closing. Regulate to 15 lbs. pressure. At this pressure, autoclave for 20 minutes.
Cleaning the Microscope
- The Eyepiece: To remove dust, brush with a camel’s hair brush. To remove grease film, use isopropyl alcohol on lens paper and then use a dry piece of lens paper to remove the isopropyl alcohol. To check, tip the eyepiece to reflect the light. If the eyepiece is to be removed from the tube for any length of time, plug the tube to prevent dust from collecting on the back surfaces of the objectives.
- The objectives: Clean as above. To check, use a hand lens to examine the lenses.
- The mirror: Clean the surface with distilled water on lens paper, then dry it with a clean piece of lens paper.
pH Defined
The concentration of hydrogen ions (power of hydrogen ion concentration) in solution when the concentration is expressed as gram-ionic weights per unit. The form used to express pH is the negative logarithm of this concentration. pH readings less than 7 are acids; those above 7 are alkalines.
Making a Buffering Solution
Buffers are compounds or pairs of compounds that have the chemical capacity to resist changes in pH. To prepare a standard phosphate buffer, follow one of the protocols.
- To make a .067 M solution of Na2HPO4, add 9.46 g per 1 L distilled water.
- To make a .067 M solution of NaH2PO4•H2O, add 9.2 g per 1 L distilled water.
Dilute the solutions in the volumes listed below to 200 ml with distilled water to make the appropriate buffer.
| Na2HPO4 (ml) | NaH2PO4 (ml) | pH |
| 0.5 | 19.5 | 5.3 |
| 3.9 | 16.1 | 6.2 |
| 12.2 | 7.8 | 7.0 |
| 18.4 | 1.6 | 7.8 |
| 19.5 | 0.5 | 8.3 |
Preparing Molar and Normal Solutions
- Molar (M) Solutions contain one gram molecular weight of dissolved substance in one liter of solution. The gram molecular weight of a substance is determined by calculating the total atomic weights in the molecule indicated by the chemical formula for that substance and then using that amount in grams.To calculate the mass of a substance needed to make a solution at a certain molarity:m = M x Mr x Vwhere:
m = mass of substance in grams
M = molarity of solution
Mr = molecular weight of substance
V = volume of solution in liters - Normal (N) Solutions contain one gram equivalent weight of dissolved substance in one liter of solution. The gram equivalent weight is determined by calculating the molecular weight of the substance divided by the number of positive or negative ionic charges, and using that figure in grams. Thus the gram equivalent weight of HCI equals its gram molecular weight, but that of H2SO4 is 1⁄2 its gram molecular weight.To calculate the mass of a substance needed to make a solution at a certain normality:m = (N x Mr x V) / Valencywhere:
m = mass of substance in grams
N = normality of solution
Mr = molecular weight of substance
V = volume of solution in liters
Valency = number of hydrogen atoms (equivalent) which an atom could combine with or displace
Useful Reagents
- Saline solution for invertebrates: Add 0.6 g NaCl to 100 ml H2O.
- Saline solution for frog tissue: Add 0.75 g NaCl to 100 ml H2O.
- Saline solution for mammalian tissue: Add 0.9 g of NaCl to 100 ml H2O.
- To discharge trichocysts of Paramecia: Use 1.0% aqueous solution of tannic acid.
- To discharge to nematocysts of Hydra: Use 5.0% aqueous solution of NaCl.
Common Preservatives and Fixatives
Formalin in its concentrated form is formaldehyde gas dissolved in water to a 40% concentration. When preparing percentage solutions, treat formalin as 100% in calculating dilutions. It may be used in various strengths, depending on the size of the specimen, for anything plant or animal. A 10% solution will, however, satisfactorily preserve most specimens.
FAA (Formalin/Acetic acid/Alcohol) is used for preserving plant tissue:
Ethyl alcohol (85%)………………………50 ml
Glacial acetic acid ……………………… 2 ml
Formalin (40%) …………………………10 ml
Water………………………………………40 ml
Bouin’s Fixative:
Picric acid (saturated
aqueous solution) ………………………75 ml
Glacial acetic acid ……………………… 5 ml
Formalin (40%) …………………………25 ml
To avoid deterioration of the solution, it is best to add the picric acid just before you use it. However, the shelf life of the complete solution is six to eight months.
General Zoological Stain
Borax Carmine
To prepare a stock stain solution, add 1 g Borax Carmine to 100 ml distilled water. Boil for 1/2 hour. Cool, filter, and combine with 100 ml of 70% alcohol. Let stand for two days and filter.
To prepare a specimen for stain, you must first dehydrate the specimen using 30% and 50% alcohol. Prepare the stain by adding 20 ml of stock Borax Carmine stain (see above) to 80 ml of 70% alcohol. Overstain the tissue. Then place it in 70% acid alcohol made by adding 1 ml of concentrated HCI to 99 ml of 70% alcohol. The tissue must be checked periodically to get proper destaining. After the tissue has been destained, it must be dehydrated again using 85%, 90%, 95%, and absolute alcohol. Rinse in xylene and mount.
General Botanical Stain
Safranin O and Light Green SF Y
To prepare stock stain solutions:
Safranin O……………………………………1 g
50% alcohol……………………………… 99 g
Light Green SF Yellowish…………………0.2 g
100% alcohol ……………………………50 ml
Clove oil …………………………………50 ml
To prepare a specimen for stain, you must first dehydrate the specimen in cellosolve for 2 minutes; then place it in Safranin (time will vary with tissue being stained). Move the tissue to cellosolve for one minute to remove the excess stain and then counterstain in Light Green for 2 minutes. Place the tissue in clove oil to remove the excess Light Green, run it quickly through xylene, and mount it in balsam.
Temperature Conversion Formulas
Fahrenheit to Centigrade: C° = 5/9 x [F° – 32]
Centigrade to Fahrenheit: F° = 9/5 x C° + 32
Mohs’ Scale of Hardness
- Talc
- Gypsum
- Calcite
- Fluorite
- Apatite
- Orthoclase feldspar
- Quartz
- Topaz
- Corundum
- Diamond
Weight, Length, and Volume Conversions
1 gram = .03527 ounces
1 kilogram = 2.205 pounds
1 ounce = 28.35 grams
1 pound = 453.6 grams
1 micron = 1/1000 millimeter or 1/25,400 inch
1,000 millimeters = 1 meter
1 centimeter = .3937 inches
1 meter = 3.281 feet or 39.37 inches
1 inch = 2.54 centimeters
1 foot = 30.48 centimeters
1 cubic centimeter = 1 milliliter (water at 4°C)
1,000 milliliters = 1 liter
1 liter = 1.056 U.S. liquid quarts
1 U.S. fluid ounce = 29.57 milliliters
1 teaspoon = 4.93 cubic centimeters
