chemistry, Stoichiometry

2009-03-27 3:16 pm

A researcher is performing some experiments on an unknown metal. First she takes a rectangular block of the metal measuring: 17.41 mm wide by 13.70 mm high by 54.76 mm long and finds that its mass is 79.804 grams. The experimenter then grinds part of this block into metal shavings. She then completely burns 1.19 cubic centimeters of the metal shavings in pure oxygen. Following the reaction all that remains is a white powdery product. She carefully weighs the product and finds that the mass is 10.696 grams. Further experimentation shows that the unknown metal in the product has a +3 oxidation state.

Based on this information, what is the

A)AMU (molecular mass)

B)identity of the unknown metal?
(enter the name of the metal, for example, "gold")

It is a challanging problem its really hard can anyone help me step by step thankyou

回答 (1)

老爺子

2009-03-27 7:16 pm

✔ 最佳答案

A)
Denote the metal as M.
Let y (a.m.u) be the relative atomic mass of M.

Volume of the rectangular block of metal M
= (1.741 cm) x (1.370 cm) x (5.476 cm)
= 13.06 cm3

Density of the metal M
= 79.804/13.06
= 6.111 g cm-3

A metal oxide is formed when M is burned in pure oxygen.
In the oxidation, the oxidation state of M is +3.
The formula of the oxide of M is M2O3.

Mass of metal M to make the M2O3
= Density x Volume
= 1.19 x 6.111
= 7.272 g

Mass of O in M2O3
= 10.696 - 7.272
= 3.424 g

Mole ratio M : O
7.272/y : 3.424/16 = 2 : 3
3(7.272/y) = 2(3.424/16)
y = 50.97

The relative atomic mass of the metal = 50.97 (a.m.u.)

B)
Refer to the Periodic Table.
The metal is "vanadium".
=

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