Determine the fineness of the gold ring if the ring weighing 12 g contains 40%

Determine the fineness of the gold ring if the ring weighing 12 g contains 40% copper and 22.5% silver. Find the mass of all the metals contained in the ring.

Given:
m (rings) = 12g
ω (Cu) = 40%
ω (Ag) = 22.5%

To find:
gold content – ?
m (Au) -?
m (Cu) -?
m (Ag) -?

Decision:
1) m (Cu) = ω (Cu) * m (rings) / 100% = 40% * 12/100% = 4.8 g;
2) m (Ag) = ω (Ag) * m (rings) / 100% = 22.5% * 12/100% = 2.7 g;
3) m (Au) = m (rings) – m (Cu) – m (Ag) = 12 – 4.8 – 2.7 = 4.5 g;
4) ω (Au) = m (Au) * 100% / m (rings) = 4.5 * 100% / 12 = 37.5% – 375th sample of gold.

Answer: Gold fineness – 375th; the mass of Cu is 4.8 g; weight of Ag – 2.7 g; Au mass – 4.5 g.