### F.7

Posted:

**Mon Oct 08, 2018 3:19 pm**How do I find the molar mass of the metal? I did 2x/2x+16 = .888 and solved for x. I got x as 63.43g but that is wrong. Please let me know what I did wrong!

Created by Dr. Laurence Lavelle

https://lavelle.chem.ucla.edu/forum/

https://lavelle.chem.ucla.edu/forum/viewtopic.php?f=11&t=33316

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Posted: **Mon Oct 08, 2018 3:19 pm**

How do I find the molar mass of the metal? I did 2x/2x+16 = .888 and solved for x. I got x as 63.43g but that is wrong. Please let me know what I did wrong!

Posted: **Mon Oct 08, 2018 3:21 pm**

Please post the question also.

Posted: **Mon Oct 08, 2018 3:26 pm**

Can you please post the question in its entirety? Thank you.

Posted: **Mon Oct 08, 2018 3:26 pm**

A metal M forms an oxide with the formula M20, for which the mass percentage of the metal is 88.8%. (a) What is the molar mass of the metal? (b)Write the name of the compound.

Posted: **Mon Oct 08, 2018 4:26 pm**

(a) If we assume the compound to be 100g, then 88.8 g is M and 11.2 g would be O. First, find the molar mass of the whole compound through stoichiometry: (100 g M2O/11.2 g O) x (16.00 g O/1 mol O) x (1 mol O/1 mol M2O) will result in 143 g/mol M2O. Since O's molar mass is 16.00 g/mol, the molar mass of M2 is 143-16=127 g/mol, meaning the molar mass of the metal M is 127/2= 63.5 g/mol.

(b)Look on the periodic table, and the closest metal with the molar mass of 63.5 g/mol is Copper. Thus, its name would be Cu2O, or copper(I) oxide. Hope this helps!

(b)Look on the periodic table, and the closest metal with the molar mass of 63.5 g/mol is Copper. Thus, its name would be Cu2O, or copper(I) oxide. Hope this helps!

Posted: **Wed Oct 10, 2018 12:30 am**

Suppose that the mass of O atoms is 16g, according to the question, the percentage of O atoms is(100%-88.8%)=11.2%. Therefore, the molar mass of M2O would be 142.8g*mol^-1. So the molar mass of M is 63.4g*mol^-1, M is copper.