sample of pure Cu (4.00 g) heated in a stream of oxygen for some time, gains in weight with the formation of black oxide of copper (CuO) . The final mass is 4.90 g. What percent of copper remains unoxidized (C
Answers
Answer:
ANSWER
Milli-moles of KI=50×0.04=2
Milli-equivalents of Na
2
S
2
O
3
reacted with 10 mL solution=20×2.5×10
−3
=50×10
−3
Milli-equivalent of I
−
left unreacted in 100 mL solution=50×10
−3
×
10
100
=0.5
Milli-moles of I
−
reacted with CuCO
3
=2−0.5=1.5
∵2Cu
2+
+5I
−
→2CuI+I
3
−
Milli-moles of Cu
2+
=
5
2
×1.5=0.6
Weight of CuCO
3
=0.6×10
−3
×123.5=0.0741
Weight % of CuO
3
=
0.1
0.0741
×100=74.1
Given:
The mass of pure copper = 4 gm
The final mass = 4.9 gm
To Find:
The percentage of copper that remains unoxidized.
Calculation:
- Let the mass of oxidised Cu be x gm
⇒ The mass of unoxidised Cu = (4 - x) gm
- The mass of CuO formed = {4.9 - (4 - x)} gm ....(i)
- The oxidation of copper is given as:
Cu + O → CuO
⇒ The mass of CuO produced by 63.5 gm of Cu = 79.5 gm
⇒ The mass of CuO produced by x gm of Cu = {(79.5/63.5) × x} gm ....(ii)
- From (i) and (ii), we have:
{4.9 - (4 - x)} = {(79.5/63.5) × x}
⇒ 0.9 + x = 1.252 x
⇒ 1.252 x - x = 0.9
⇒ 0.252 x = 0.9
⇒ x = 0.9 / 0.252
⇒ x = 3.57 gm
- So, the mass of unoxidised Cu = (4 - x) = 4 - 3.57 = 0.43 gm
- The percentage of unoxidised Cu = (0.43/4) × 100 = 10.75 %