Question

An alloy has Fe, Co, and Mo equal to 71% , 12% and 17% respectively. How many cobalt atoms are there in a cylinder of radius 2.5cm and a length of 10 cm ? Density of alloy is 8.2 g/ml atomic mass of cobalt = 58.9

Answer 1

From the given,  

$Radius\quad of\quad the\quad cylinder\quad =\quad 2.5\quad cm$

$Length\quad of\quad the\quad cylinder\quad =\quad 10\quad cm$

$Density\quad of\quad alloy\quad =\quad 8.2\quad g/ml\\ Volume\quad of\quad cylinder\quad =\quad \pi { r }^{ 2 }h$

$Substitute\quad the\quad given\quad values\quad =\quad 3.14\times \quad (2.5{ ) }^{ 2 }\times \quad 10$

$=\quad 196.5\quad c{ m }^{ 3 }$

$Mass\quad =\quad Volume\quad \times \quad density$

$=\quad 196.5\quad c{ m }^{ 3 }\quad \times \quad 8.2\quad g/{ cm }^{ 3 }$

$=\quad 1609.25\quad g$

$Mass\quad of\quad cobalt\quad =\quad \frac { 12 }{ 100 } \quad \times \quad 1609.25\quad g\quad =193.11\quad g$

$Moles\quad of\quad cobalt\quad =\quad \frac { Mass }{ Atomic\quad mass\quad of\quad cobalt\quad  } \quad =\quad \frac { 193.11\quad g }{ 58.93\quad g/mol } \quad =\quad 3.277\quad mol$

Total\quad cobalt\quad atoms\quad =\quad Moles\quad of\quad cobalt\quad \times \quad Avagadro\quad number

$=\quad 3.277\quad \times \quad 6.023\quad \times \quad { 10 }^{ 23 }$

$=\quad \quad 1.97\quad \times \quad { 10 }^{ 24 }\quad atoms\quad$

Answer 2

Answer:

19.8*10^23

Explanation:

the above method done is absolutely correct