Question

*7.91. Mining for Gold Gold can be extracted from the surrounding rock using a solution of sodium cyanide. While effective for isolating gold, toxic cyanide finds its way into watersheds, causing environmental damage and harming human health. 4 Au(s) + 8 NaCN(aq) + O2(g) + 2 H2O(l) → 4 NaAu(CN)2(aq) + 4 NaOH(aq) 2 NaAu(CN)2(aq) + Zn(s) → 2 Au(s) + Na [Zn(CN)4](ag) a. If a sample of rock contains 0.009% gold by mass, how much NaCN is needed to extract the gold as NaAu(CN), from 1 metric ton (10 kg) of rock?

Answer 1

(Ib t Mass of ro ck = lo ka 3 Au in the Mass of ma ss ot gold = 90 chimical equation, mol of gold extract NacN Can = 8 x44 almol = 392 q Mass ot NacN = +88 =4メ194 9mo Mass of gold NaCN So, 392 g 88 Au 392 Au 90 44.7 788 Mass of Nacu vequired hemical equation, キxom the ] mol Zn 2 mol NaAu CCN) nue ds mol Zn nueds Au 2 Mo OR 65.37 2n 2x197 Au 65.37 Au 2メ194 Mass of 3inc nueded = 14.93 9

90 Mass 3 = 4.663 cm c) Volume of gold density 19.3 a/cm a' cm, Then be Let tha ength of go ube 3 u.663 u 3 =a cube Volume of cube of length 67 cm the gold ingot Hence