A PRIMER ON MOLECULAR WEIGHTSThe first chemical reaction that takes place when making the yttrium-barium-copper oxide superconductors is: 0.5 Y_{2}O_{3} + 2 BaCO_{3} + 3 CuO = YBa_{2}Cu_{3}O_{6.5} + 2 CO_{2}In order to obtain the correct ratio of the starting ingredients, it is necessary to have the correct molecular ratios. Since all of the atoms and molecules have different weights, the weight ratios of the atoms and molecules must be known before the correct weight ratios of the chemical powders can be calculated. The For Y For O Molecular Weight of Y Therefore 225.88 grams of yttrium oxide contains 6.02 x 10 Since the atomic weight of barium is 137.33 and the atomic weight of carbon is 12.011, the molecular weight of barium carbonate can be calculated in a similar fashion to be 197.35. Since the atomic weight of copper is 63.546, the molecular weight of cupric oxide is 63.546 + 15.9994 = 79.5454. Therefore the proper ratios for the desired chemical reaction are: - 0.5 x 225.88 =
**112.94 grams of Y**_{2}O_{3} - 2 x 197.35 =
**394.7 grams of BaCO**_{3} - 3 x 79.5454 =
**238.6362 grams of CuO**
Since these weights are the correct ratios, they can all be multiplied or divided by any number to obtain more convenient quantities in the proper ratios. By dividing by 10 (and doing some rounding off), we obtain these weights: **11.29 grams of yttrium oxide****39.47 grams of barium carbonate****23.86 grams of cupric oxide**
The result of mixing and heating the chemicals of this combination of weights will be 6.02 x 10 |