relation sheep between conductivity ph and co2

8/6/2019 Relation Sheep Between Conductivity Ph and Co2

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N o . 5 SALAMANDERS OF SE OHIO 303

RELATIONSHIP BETWEEN TOTAL ALKALINITY,CONDUCTIVITY, ORIGINAL pH, AND B UFFE RACTION OF NATURAL WATERRALPH E. S E C H R I E S T f

Department ofBiology, Bowling Green State University, Bowling Green, OhioINTRODUCTIONIn an effort to elucidate the properties of water related to the carbon supplyfor living organisms, thebuffer action, conductivity, and total alkalinity of variousnatura l waters were studied. N atu ral waters around Bowling Green, Ohio, weresampled at various times: Urschel's Quarry in Bowling Green being sampledmost frequently; Klein's Well represented a soft ground water drawn directlyfrom the ground by a pump; Poe Ditch was contaminated by sewage.Dye (1944), using equilibrium equations of Moore (1939), produced nomo-graphs for the relationship between pH, total alkalinity, and the three forms ofcarbon dioxide (free carbon dioxide, carbonate, and bicarbonate). However,Verduin (1956a) showed that these nomographs do not give a valid relationshipbetween pH change and carbon dioxide change in natural water. The valuesobtained from the equilibrium equations donot agree with the actual data fromSandusky Bay, ocean water, and Lake Erie which Verduin (ibid.) has reported.Moberg et al. (1934) showed that their theoretical values do not completely agree

with their computed values for ocean water. In the pH range from 6.0 to 8.0,observed linear increase of carbon dioxide content with decreasing pH is not infPresent address: Department of Zoology and Entomology, Ohio State Universi ty,Columbus 10.

T H E O H I O JOURNAL OF SCIENCE 60(5): 303, September, 1960.


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30 4 RALPH E. SECHRIEST V ol . 60line with the theoretical values predicting an exponential increase in this region.Thus, other factors appear to influence the buffering capacity of natural waters.

METHODSThe samples were dipped from the surface of the water body in a 1,000 mlflask and returned to the laboratory, where the fresh samples were processedimmediately. The aerated samples were allowed to reach equilibrium w ith theatmospheric CO2 by standing at a depth of 2 cm in a large pan for at least24 hr before processing.A Barnstead Purity Meter (Model PM-3) was used to measure the electricalconductivity (Daniels et al., 1941). The m eter was calibrated in megohms(Mohm) resistance and has a built-in tem peratu re correction rheostat. Theelectrical conductance in mho of a 100-ml sample of distilled water was measured.The equipment was then rinsed thoroughly with distilled water. A sample ofnatural water was then diluted 1:50 with distilled water, mixed, and the con-ductiv ity measured. Then, 1:100 and 1:200 dilutions of the na tural water weremade and also measured for conductivity. The average of the three readingswas computed to make the data more reliable.A Beckman pH Meter (Model G) was used to support total alkalinity andbuffering action titrations by methyl orange and pehnolphthalein indicatormethods (Kline, 1955; Bull, 1943). After three drops of phenolphthalein indicatorhad been added, 0.01 N H2SO4 or 0.02 N NaOH were titrated into the sampleuntil the end point had been reached. Then , 1 ml of tit ra te at a time wasadded in excess until a total of 5 ml had been added. The total alkalinity wasmeasured by titration to the visual end point with 0.01 N H2SO4, using methylorange indicator (Welch, 1948). The pH of the sample was measured before,during (in the case of phenolphthalein), and after titration.Results of the phenolphthalein titration were graphed on arithmetic graphpaper. From these buffer curves the micromoles of CO2 per liter per pH unitwere calculated for each four-tenths of a pH unit change. These da ta were thengraphed against total alkalinity, original pH of the water, and conductivity.Standard statistical computations were made (Snedecor, 1946). Since Klein'sWell and Poe Ditch data were noticeably different from the natural water data,they were omitted from the statistical computations but were placed in the graphsfor comparison.

RESULTSThe da ta were compared by means of graphs. Since the hydrogen ions andthe hydroxyl groups react w ith an; equal num ber of carboxyl groups, the m icro-moles of carbon dioxide change per unit of pH change can be computed from sucha graph as follows:

ml titrate X10 ^tmole C02/ml titrate , ,., TT . ,a i l x 0 4 p H u n i t = Mmole CO,/(1 P H unit)Typical values for the buffer curve were 462.5 jumole of CO 2/(1 "pH uni t) for thepH range 7.0-7.4; 475 for the pH range 7.4-7.8; 500 for pH range 7.8-8.2; 450for pH range 8.2-8.6; 700 for pH range 8.6-9.0; and 1025 for the pH range 9 .0-9.4.The conductivity graphed against the total alkalinity of the natural watersamples (fig. 1) increased as the to ta l alkalinity increased. The coefficient ofcorrelation (r= 4-0.72) was highly significant, statistically (P=


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No. 5 CARBON SUPPLY FROM WATER 305to tal alkalinity and has a correlation coefficient of +0.76 (P = 0.02). All otherpH ranges studied (7.0-9.4) showed similar positive, statistically significantcorrelations.Conductivity graphed against the slope of the buffer curve in pH range 7.4to 7.8 has a correlation coefficient of +0.32, and this graph was representative ofthe other pH ranges. The produc t of total alkalinity and conductivity wasgraphed against the slope of the buffer curve (fig. 3) to learn whether this product

o - Natura l Water (A era ted ) - Natu ral Water (Fr es h)A - Poe Ditch ( A er at ed )x - Klein's Well (A er ate d )

0 2 0 4 0 60 80 100 120TOTAL ALKALINITY, ml. of HgS04(0.01 N.)FIGURE 1. Relation of conductivity to total alkalinity.

would show a higher correlation than each property by itself. There is a widevaria tion to the dat a; however, a correlation coefficient of +0. 52 (P = 0.04) wasfound. The correlation coefficient is greater than conductivity graphed againstthe slope, and less tha n tota l alkalinity graphed against the slope of the buffercurve. This then showed th at factors other than the forms of carbon dioxide affectbuffer action, but these have not been investigated. A summ ary of the statisticalanalyses appears in table 1.DISCUSSION AN D CONCLUSIONS

Variation in limnological da ta is normal and to be expected. Powers (1939)found a range of over one pH unit in the blood pH and aerated serum withinthe same species of fish. The relation of Secchi disc readings to the depth asso-ciated with one percent of surface light presents also a scatter of the data (Verduin,1956b). The photosyn thetic rate at optimal light intensity vs. respiration ratedem onstrates a wide range w ith values ranging from 0.25 to 14 /zmole of CO 2/r) (Verduin, 1956a). In terres trial biological da ta variation is also observed,

CONDUCTVITYxIO~MHO


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No. 5 CARBON SUPPLY FROM WATER 307an d the absence of carbonic acid (Welch, 1948; Verduin, 1959). However, inthis study no significant differences were found between the aerated and freshsamples. Thus, an aerated sample must contain some carbonic acid while thecarbonates must be practically absent. Carbon dioxide is continually enteringthe water, converting to carbonic acid, and changing the carbon dioxide intobicarbonates. Thus, phenolphthalein alkalinity measures the hydroxyl ionsrather than the carbonates, as one is sooften led to believe.Poe Ditch and Klein 's Well differ markedly from natu ral water. Samplesfrom these two sites had a much higher electrical conductance and total alkalinity,

0-N atu ral Water (A.) -Natural Water(F. )A-Poe Ditch (A.)x-Klein's Well (A.)

0 400 800 1200 1400 2 0 0 0SLOPE OF BUFFER CURVE

(MICROMOLES CO2/L/pH UNIT )FIGURE 3. Relation of product of conductivity and total alkal ini ty to slope of buffercurve (pHrange 8.2-8.6).

but the slopes of the buffer curves were intermediate to those for natural water.The product of total alkalinity and conductivity, as might be expected, furtherseparated the ditch and well samples from the natural waters.Factors other than the various forms of carbon dioxide affect buffering action.Since the coefficient of correlation of total alkalinity vs. the slope of the buffercurve (r=+0.52) is intermediate between conductivity vs. slope (r=+0.32) andtotal alkalinity vs. slope (r=+0.76), other unmeasured ions affect the buffercurve. When the product of conductivity and total alkalinity was graphed againstslope, the unmeasured ions were partially masked; when total alkalinity wasgraphed against slope, the unmeasured ions were entirely absent, thereb y, resultingin a high coefficient of correlation.However, these studies have not explained the wide variation in the slopes ofthe buffer curves. Verduin (1956a) has shown differences in the buffer curves fora standard sodium bicarbonate solution, ocean water, Sandusky Bay water, andLake Erie water; and the present study revealed similar results.

CONDUCTVIT

xTOTLALKALINITY


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30 8 RALPH E. SECHRIEST V ol . 60TABLE 1

Summary of statistical analyses*

pH vs. SlopeConductivi ty vs.total alkal ini tyConductivi ty vs.slopeTotal alkal ini tyvs . slopeTotal alkal ini ty Xconductivity vs.slope

N1134142116

01000

12

b x y.0011.9 9.4 7.021.74

b :64 .

0 .0 .

30 .

0 .

yx

2404 7223421

05011

t b.8 5.3 6.9 6.1 4.7 3

P b

relation sheep between conductivity ph and co2

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