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TABLE 8.14<br />

National Bureau of Standards (U.S.) Reference pH Buffer Solutions<br />

Temperature<br />

C<br />

Secondary<br />

standard<br />

0.05 M<br />

K<br />

tetraoxalate<br />

KH tartrate<br />

(saturated at 25C)<br />

0.05 M<br />

KH 2<br />

citrate<br />

0.05 M<br />

KH<br />

phthalate<br />

0.025 M<br />

KH 2 PO 4 ,<br />

0.025 M<br />

Na 2 HPO 4<br />

0.0087 M<br />

KH 2 PO 4 ,<br />

0.0302 M<br />

Na 2 HPO 4<br />

0.01 M<br />

Na 2 B 4 O 7<br />

0.025 M<br />

NaHCO 3 ,<br />

0.025 M<br />

Na 2 CO 3<br />

Secondary<br />

standard Ca(OH) 2<br />

(saturated at 25C)<br />

0 1.666 3.860 4.003 6.984 7.534 9.464 10.317 13.423<br />

5 1.668 3.840 3.999 6.951 7.500 9.395 10.245 13.207<br />

10 1.638 3.820 3.997 6.923 7.472 9.332 10.179 13.003<br />

15 1.642 3.802 3.998 6.900 7.448 9.276 10.118 12.810<br />

20 1.644 3.788 4.002 6.881 7.429 9.225 10.062 12.627<br />

25 1.646 3.557 3.776 4.005 6.865 7.413 9.180 10.012 12.454<br />

30 1.648 3.552 3.766 4.011 6.853 7.400 9.139 9.966 12.289<br />

35 3.549 3.759 4.018 6.844 7.389 9.102 9.925 12.133<br />

38 1.649 3.548 3.756 4.030 6.840 7.384 9.088 9.910 12.043<br />

40 1.650 3.547 3.753 4.035 6.838 7.380 9.068 9.889 11.984<br />

45 3.547 4.047 6.834 7.373 9.038 11.841<br />

50 1.653 3.549 3.749 4.050 6.833 7.367 9.011 9.828 11.705<br />

55 3.554 4.075 6.834 8.985 11.574<br />

60 1.660 3.560 4.081 6.836 8.962 11.449<br />

70 1.671 3.580 4.116 6.845 8.921<br />

80 1.689 3.609 4.164 6.859 8.885<br />

90 1.72 3.650 4.205 6.877 8.850<br />

95 1.73 3.674 4.227 6.886 8.833<br />

Dilution value<br />

pH 1/2 0.186 0.049 0.024 0.052 0.080 0.070 0.01 0.079 0.28<br />

Source: R. G. Bates, J. Res. Natl. Bur. Stand. (U.S.), 66A:179 (1962) and B. R. Staples and R. G. Bates, J. Res. Natl. Bur.<br />

Stand. (U.S.), 73A:37 (1969).<br />

Note: The uncertainty is 0.003 in pH in the range 0–50C, rising <strong>to</strong> 0.02 above 70C.<br />

8.105

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