TIPS AND TRICKS FOR RUNNING A SUCCESSFUL CHEMISTRY LABORATORY Dr. Kris Sherman Teach North Texas University of North Texas

PURPOSE You will receive a “how-to” on the following: ► Maximizing student time by setting up labs for student success success ► Microscale labs ► Solution preparation – from scratch, diluting solutions, making solutions with the correct molarity, % concentration making solutions with the correct molarity, % concentration ► Storing chemicals from year to year ► Preservation of lab specimens for tonight’s dinner By participating in this hands-on session, you will become a better Chemistry teacher and laboratory manager. These tips and tricks will save you time and money.

LAB PREP Plan your time wisely! Give yourself at least 3 days lead time. Take into account ALL students that will complete the lab, especially if you are preparing lab for all the Chemistry teachers.

Have a central location for solution making and lab prep (and keep it clean! ).

Never put reagent bottles out for student use. Use dispensing containers such as dropper bottles, beakers and disposable pipets.

If you are in charge of setting up lab for a team of teachers, be sure to divide up the chemical supplies so that the teachers can pick up their set and take to the lab. Plastic washtubs and carts are a convenient way of sorting and carrying chemicals to labs.

In the lab, chemicals can be set out two ways: a set at each station or all chemicals at one central location.

If a lab has several distinct parts that don’t rely on the others, setting the lab up with stations is effective for time and equipment management. Be sure to label stations appropriately.

MICROSCALE LABS ► Microscale labs developed as a response to environmental concerns about chemistry labs. ► Microscale labs tend to involve drops of chemicals or a few mL at most. ► Microscale labs have been designed for most concepts taught. ► Microscale labs are very economical and involve little hazardous waste. ► They are usually more time effective for students and are safer for students.

POST LAB NEEDS ► Clean up is vital! Everyone participates! ► Make students clean up and put away the equipment they use. ► Consolidate left-over chemicals appropriately. Solids stored in different container from reagent bottle. Solutions put in storage bottles. Contamination by students is highly likely if not certain.

Storing Extra Solids

CHEMICAL STORAGE ► Your store room should be organized using a standard method that follows OSHA and state regulations. ► Store solutions in a separate place from the solid reagents. Exceptions would be flammable materials and corrosives. ► Save dropper bottles and dropping pipets with solutions if you’re using them again and won’t deplete the supply.

CHEMICAL STORAGE

SOLUTION PREPARATION 1. Solid reagents that are dissolved in a solvent. 2. Stock solutions that are diluted.

WHAT IF I HAVE TO MAKE A SOLUTION FROM SCRATCH??? 1. Calculate the mass of solute needed using: Molarity (M) x volume (L) x molar mass (g/mol) 2. Measure out the mass of solute you calculated. Measure out the volume of solvent needed – matches the volume of solution. 3. Stir to dissolve. Heat if needed. 4. Transfer the solution to an appropriate storage bottle and label the bottle with the formula or name of the solution, the concentration of the solution, and the date the solution was made.

EXAMPLE How much sodium nitrate, NaNO 3, is needed to make 350 mL of a 3.2 M solution? Given: V = 350 mL = L M = 3.2 mol/L molar mass = g/mol (from periodic table!) Find: mass of NaNO 3 M x V x molar mass = mass of solute M x V x molar mass = mass of solute (3.2 mol/L) x (0.350 L) x ( g) = mass of solute 95.2 g = mass of solute 95.2 g = mass of solute Measure out 95.2 g NaNO 3 and dissolve in 300 mL water. Dilute to 350 mL. Stir.

HOW DO I DILUTE A SOLUTION? 1. Calculate the volume of stock solution needed by using the following equation: M 1 x V 1 = M 2 x V 2 where M 1 and V 1 are for the stock solution and M 2 and V 2 are for the dilute solution. where M 1 and V 1 are for the stock solution and M 2 and V 2 are for the dilute solution. 2. Measure out the volume of stock solution you calculated, put into a volumetric flask, and add water until you reach the volume you need for the dilute solution (V 2 ). 3. Transfer the solution to an appropriate storage bottle and label the bottle with the formula or name of the solution, the concentration of the solution, and the date the solution was made.

EXAMPLE I need a 2.5 L of a 0.02 M potassium permanganate solution for an upcoming lab. In my stockroom, I have a bottle of 15 M potassium permanganate. How much of the stock solution will I need? How do I make the solution? Given: M 1 = 15 mol/L M 2 = 0.02 mol/L V 2 = 2.5 L Find: V 1 M 1 x V 1 = M 2 x V 2 V 1 = M 2 x V 2 V 1 = M 2 x V 2 M 1 M 1 V 1 = (0.02 mol/L) x (2.5 L) V 1 = (0.02 mol/L) x (2.5 L) 15 mol/L 15 mol/L V 1 = L = 3.33 mL V 1 = L = 3.33 mL **Turning the L in the answer to mL is practical because 3.33 mL is easier to measure than L! 3.33 mL is easier to measure than L!

DILUTING ACIDS ► ALWAYS add acid to water. Acids react with water very exothermically. The solution formed will steam and could become very hot to touch. ► Hydrochloric acid, ammonium hydroxide, and acetic acid fume heavily. Make dilutions from the concentrate in the ventilation hood.

WHAT ABOUT PERCENT CONCENTRATION? Percent is a proportion of a quantity to 100. Be aware of the types of percent concentrations: Percent is a proportion of a quantity to 100. Be aware of the types of percent concentrations: % m/m (mass of solute/100 g of solution) % v/v (volume of solute/100 mL of solution – used frequently with liquid solutes in liquid solutions) % m/v (mass of solute/100 mL of solution – used most often and with solid solutes in liquid solvents)

EXAMPLE For a titration of a weak acid lab, various vinegar samples are used. Starting with 5% vinegar from the local grocery store, concentrations of 2.5% and 1.25% are needed. If 500 mL of each concentration are needed, how much 5% vinegar will be diluted? Using the fact that percent concentration is a proportion, set up ratios to solve for the volume of solute (vinegar): 2.5 mL = X mL 100 mL 500 mL 100 mL 500 mL 12.5 mL = X 12.5 mL = X