Question

A 67.2 g sample of a gold and palladium alloy contains 3.10x1023 atoms. What is the mass percentage of the gold in the alloy? VO A A O O ? Submit Previous Answers Request Answer * Incorrect; Try Again; 5 attempts remaining Part B What is the mass percentage of the palladium in the alloy? PO ALOM O O ? Submit Request Answer

Answer 1

Number of mol of sample = number of atoms / Avogadro’s number
= 3.10*10^23 / (6.022*10^23)
= 0.515 mol

Let mol of Gold be x.
Then mol of Palladium = 0.515-x

Total mass = mol of gold * molar mass of gold + mol of Palladium * molar mass of Palladium
67.2 = x * 196.97 + (0.515-x)*106.42
67.2 = x * 196.97 + 54.806 - 106.42*x
12.394 = 196.97*x - 106.42*x
12.394 = 90.55*x
x = 0.1369 mol

So,
Mass of gold = x * 196.97
= 0.1369 * 196.97
= 26.97 g

A)
Mass % of gold = mass of gold * 100 / total mass
= 26.97 * 100 / 67.2
= 40.1 %

Answer: 40.1 %

B)
Mass % of Palladium = 100 - Mass % of gold
= 100 - 40.1
= 59.9 %

Answer: 59.9 %