Can we determine the atomic weights of zinc and copper from this experiment? How? What other information is needed?  Experiment AThe mass of a copper turnings is determined. Heat the copper with...

Can we determine the atomic weights of zinc and copper from this experiment? How? What other information is needed?

 

Experiment A

The mass of a copper turnings is determined. Heat the copper with excess sulfur. The product mass is determined.

Result: Mass of copper: 1.70g
           Mass of copper sulfide: 2.48g

Experiment B

The mass of zinc is determined. Add sufficient 6M HCl to the zinc to dissolve all the zinc. Heat the product on the steam bath until most of the liquid was disappeared. After that heat the product until the product looking somewhat pasty while hot. Weigh the product.

Result: Mass of zinc: 0.48g
           Mass of zinc chloride :1.02g


Asked on by kadva

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jeew-m | College Teacher | (Level 1) Educator Emeritus

Posted on

As an additional data we need the atomic weights of Sulphur, Chlorine and Hydrogen.

Atomic weights

S = 32g/(mol)

Cl = 35.5g/(mol)

H = 1g/(mol)

 

`Cu_((s))+S_((s)) rarr CuS_((s))`

`Zn_((s))+2HCl_((aq)) rarr ZnCl_(2(s))+H_(2(g))`

 

Mole ratio

`Cu:CuS = 1:1`

`Zn:ZnCl_2 = 1:1`

 

Let the atomic weight of Cu is Xg/(mol) and Zn is Yg/(mol).


Cu moles used = `1.7/X`

Zn moles used = `0.48/Y`

Cus produced = `2.48/(32+X)`

`ZnCl_2` produced = `1.02/(Y+71)`

 

`Cu:CuS = 1:1`

`(1.7/X)/(2.48/(32+X)) = 1`

   `1.7/X = 2.48/(32+X)`

   `X = 69.743`

 

 

`Zn:ZnCl_2 = 1:1`

`(0.48/Y)/(1.02/(Y+71)) = 1`

 `0.48/Y = 1.02/(Y+71)`

    ` Y = 63.11`

 

Atomic weight of Cu obtaided from test = 69.743g/(mol)

Atomic eight of Zn obtained from test = 63.11g/(mol)

 

In real world;

Atomic weight of Cu = 63.546g/(mol)

Atomic weight of Zn = 65.409g/(mol)

 

So we can conclude that there will be some errors in the tests.

Sources:

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