Analysis of UC Berkeley Labs

The University of California at Berkeley has recently opened a Center for Green Chemistry in October 2009. With this addition, changes have been made to the undergraduate curriculum, attempting to make the undergraduate labs greener to better prepare future chemists for a more environmentally conscious world. Berkeley has agreed to share a few of their undergraduate lab course protocols with AGC to assess their effectiveness in terms of reagents consumed, hazard, and price. Below you will find comparisons of two distinct labs with the goal of teaching the same chemistry concept, but using different reagents and laboratory techniques. The first lab is a precipitation lab, intended for the students to understand Le Chatelier’s principle and solubility rules. The second comparison is between two separate reduction-oxidation reactions, intended to show the students a real life example of how different components of reactions can change in charge as they undergo a reaction.

 

Mana Sassanpour and John Riemann Soong

 

Comparison 1 – Precipitation lab

Old Lab New Lab
Reagent Amt Hazard, by amt Price Reagent Amt Hazard, by amt Price
Potassium chromate sol 99%+  (1 M) .5 mL, .0005 mol 3, .0015 190/500 g – .03 per student* Copper Sulfate 98%+     (3.4 M) 100 mg, .0004 mol 3, .0012 128.24/500g – .0257 per student*
Sulfuric Acid 98%         (3 M) 1 mL, .003 mol 5, .015 125/2.5 L – .01 per student* Sodium Carbonate  (.16 M) 100 mg, .0008 mol 3, .0024 126.57/500g – .0253 per                  student*
Sodium hydroxide 97%         (6 M) 1 mL, .006 mol 3, .018 157/2.5kg – .0151 per student* Vinegar  (0.84 M) 1 mL, .00084 mol 1, .00084 .53/L – neg per student
Total .0095 mol .0345 .055 per student .00204 mol .00444 .051 per student

*as purchased from www.sciencelab.com, shipping included

Figure 1: This figure records a compilation of the reagents used in the old and new labs. The first column shows concentration has indicated in the protocol. The second includes weights or volumes as indicated in the protocol and their derived amount in mols. Amounts are assuming that there is no repeat of experiments on the part of the student; it is assuming each student gets the exact amount of reagent needed and has no excess waste.

The third column shows a hazard, then weighted hazard respectively. The hazard number is obtained from Sigma Aldrich MSDS; the weighted hazard is determined by multiplying the hazard by the mols of reagent (see Appendix). Finally, the price is indicated in the fourth column. The totals are indicated in the last row.

 

Based on Figure 1, we can see that the new labs produce less waste than the old labs as the new experiment consumes .00204 mol, compared to .0095 mol. The weighted hazard for the newer lab is also lower: .00444, compared to .0345; however, the price per student for the two labs remain almost constant. Overall, the new lab appears to be more ‘green’ based on our data and analysis.

 

Next, the Barium Chromate portion of the older lab did not have a comparison in the newer lab. We have included it by itself below:

 

Barium Chromate precipitation:

Reagent Amount Hazard Price
Potassium chromate sol 99%+                       (1 M) .5 mL, .0005 mol 3, .0015 190/500 g – .03 per student*
Sulfuric Acid 98%       (3 M) 1 mL, .003 mol 5, .015 125/2.5 L – .01 per student*
Barium Chloride dihydrate 99+%       (0.1 M) 1 mL, .0001 mol 2, .0002 131.60/500 g – .0064 per student*
Hydrochloric Acid, clean room grade 38%(6 M) 1 mL, .006 mol 3, .018 204.05/3.78 L – .0267 per student*
Nitric Acid 70%          (6 M) 1 mL, .006 mol 3, .018 165.71/2.5 L – .0252 per student*
Total 4.5 mL – .0156 mol .0527 .0983 per student

*as purchased from www.sciencelab.com, shipping included

Figure 2: Above are the estimated values for the Barium Chromate precipitation experiment. Values are derived as they were in Figure 1.

 

As seen in Figure 2, the use of three strong acids (sulfuric acid, hydrochloric acid, and nitric acid) causes an increase in weighted hazard as compared to the values in Figure 1. The price per student almost doubles, and the amount generated is also much higher than both the old and new labs that are compared in Figure 1. The lab protocol was much improved by eliminating this section of the lab as it reduced waste generated by the strong acids and a chromium compound.

 

Comparison 2 – Redox Reaction lab

Old New
Reagent Amt Hazard Price Reagent Amt Hazard Price
Potassium Thiocynate 98.5%(0.1 M) 2 mL,  .0002 mol 2, .0004 243/500g – 0.01 per student* Ethanol(70%) 2 mL,  .0240 mol 5, .120 32.85/4 L – .0164 per student**
Iron (III) Nitrate 98+%(0.2 M) 0.5 mL,  .0001 mol 2, .0002 181.68/500g – 0.0147 per student* Iron (II) Sulfate 99+% .2 g, .00072 mol 2, .0014 18.2/500 g – .0073 per student**
Tea (see footnote) 1 mL, .00041mol 2, .00082 55/kg of gall – .0066 per student***
hydrogen peroxide 3%(.88 M) 1 mL, .00088 mol 3, .0026 24.45/4 L – .0061 per student**
Ascorbic acid, USP(0.1 M) 9 mL,  .0009 mol 1, .0009 135.34/500g- .043 per student *
TotalTotal for both comparisons .0003 mol.0098 mol .0006.0351 0.025 per student – 0.08 per student .02691 mol.02895 mol .12572.13016 .0794 per student – .1304 per student

*as purchased from www.sciencelab.com, shipping included

**as purchased from www.carolina.com, shipping included

***as purchased from www.alibaba.com, shipping included

Figure 3: The data are relayed in the same manner as in Figure 1, with the addition of a ‘total for both’ estimate adding data from figures one and three together. Tea data for the new lab were calculated based on recipe found here: http://www.evanlindquist.com/PDFdocuments/CooleyInk12pp.pdf. The hazard rating for the tea was based on that of tannic acid. Tannic acid was the representative solution for the gall solution.

 

 

Overall, the older labs use less reagent (in mol) and are less hazardous and costly per student. In reality, it is the oxidation-reduction experiment data that is skewing the numbers. Although the newer oxidation-reduction lab (Figure 3) attempts to be greener by using a salient life example of tea, extra steps and reagents are needed to accommodate this greener reagent. In order to dissolve it, we need ethanol, an organic reagent which is the main culprit for the dynamic difference in hazard between the two experiments.

 

Hazard estimation model

Our hazard estimation model attempts to scale calculated hazards of a reagent with both concentration and volume by multiplying the quantity of moles used with its HMIS hazard rating (RH) to yield a hazard number (NH). The overall hazard number of an experiment would then be obtained by summing the hazard numbers of each reagent used. Although crude, it is a first approach to analysing the hazards of an experiment systematically.

 

 

Future hazard quantification systems would take into better account the disproportionately troublesome hazards caused by very small amounts of very toxic chemicals (e.g. hydrofluoric acid) and very large amounts of dilute waste. Energy costs and technological costs of treatment or disposal increase with concentration on one scale, while labor costs and energy costs increase with volume on another. For large dilutions, the same amount of waste when diluted may be more expensive to treat or store compared to more concentrated waste, especially if the waste would be chronically rather than acutely toxic. RH would also be less qualitative, perhaps scaling with median lethal dose (LD50) or median toxic dose (MT50).

 

Ideally, we would have a formula which took into account both overall material (concentration x volume) but emphasised concentration and hazard rating at small volumes and took into account the greater inconvenience of large overall volume at larger volumes. We have imagined an equation of the form:

 

                              NH = RHcV(k1cRH+ k2 + k3V)

 

where k1, k2 and k3 are model-specific scaling coefficients, c is concentration and V is volume. Nevertheless, our crude model may suffice as a first approximation at laboratory scales where neither concentration or volume is a dominant factor. More information about the treatment costs and procedures of the laboratory would also be required to calibrate such a model beyond the current NH = RHcV.