# Chemistry

A compound containing boron and hydrogen has been synthesized. You perform two experiments to determine the molecular formula of the compound. A 0.492 g sample of the compound is burned in pure oxygen to produce B2O3 and 0.540 g of water. In the second experiment, when a 63.1 mg sample of the compound was placed in a 120.0 mL flask at 23 degrees C, the pressure was 98.6 mmHg. Determine the molecular formula of the compound.

1. 👍 1
2. 👎 0
3. 👁 161
1. %H in the BxHy = (g H/mass sample)*100
g H atoms (0.540 x 2/18)= about 0.0600
and %H atoms = (0.06/0.492)*100 = about 12% but you should be more accurate than that on all calculations that follow. Since the only other element is B, then B must be 100%-12% = about 88%

Now take 100 g sample that gives you about
88 g B
12 g H
Convert to mols.
88/atomic mass B = about 8
12/atomic mass H = about 12
Determine ratio which you can see is 8/8 = 1
12/8 = 1.5
so ratio is B2H3 and empirical formula mass is about 24.6

Now what's the molar mass.
PV = nRT
n = PV/RT and I obtained approx 0.00064 (again you should confirm all of these more accurately).
mols = g/molar mass and molar mass = g/mols = 0.0631/0.00064 = about 98

Molar mass is about 98; empirical mass is about 24.6 so 98/24.6 = 3.98 which rounds to 4. I suspect when you do the math more accurately it will be much closer to 4.00. So the formula is
(B2H3)4 or B8H12.

1. 👍 1
2. 👎 0

## Similar Questions

1. ### Chemistry

When 0.500 moles of boron trichloride react with 1.20 moles hydrogen gas to produce elemental boron and hydrogen chloride gas, the actual yield of boron was 66.4 % of the theoretical yield. The mass of boron obtained was _____ g.

asked by Matt on February 27, 2015
2. ### chemistry

Boron forms a gaseous compound with hydrogen with empirical formula BH3. a 1.05L sample of this compound at a pressure of 88 mm Hg at 295K has a mass of .138g. what is the molecular formula of the compound?

asked by mary on January 3, 2012
3. ### chemistry

A sample of compound containing boron and hydrogen contains 6.444 g of B and 1.803 g of H. The molar mass of the compound is about 30 g. What is its empirical and molecular formula?...thank you for sharing your knowledge...

asked by irfan on June 11, 2013
4. ### chemistry

A 2.91 gram sample of a gaseous compound that contains only boron and hydrogen has a volume of 1.22 L at 25°C and 1.09 atm. What is the formula of this compound? (Atomic Weight: H = 1.01, B = 10.8 amu) I am not sure but it is

asked by songyi on November 7, 2008
5. ### chem

When an electric discharge is passed through boron trichloride a new compound is formed. what is its simplest formula if on analysis it is shown to contain .0878 g of chlorine and .0131 g of boron?

asked by christine on December 15, 2010

1) Oxygen and boron are in the same period . When they form a compound----- is written first.Phosphorus and arsenic are the same group. When they form a compound------is written first. A) oxygen/phosphorus B)oxygen/arsenic

asked by nick on February 12, 2012
7. ### chemistry/help

1) Oxygen and boron are in the same period . When they form a compound----- is written first.Phosphorus and arsenic are the same group. When they form a compound------is written first. A) oxygen/phosphorus B)oxygen/arsenic

asked by nick on February 12, 2012
8. ### chemistry

When calling the families on the periodic chart by the top or first name in the column, where hydrogen is a non metal, and in family 13, where boron is a metaloid , is it correct to call those families the hydrogen or lithium

asked by lulu on October 12, 2016
9. ### Science

i need a bit of help finding out how to do this problem. just tell me how and ill take it from there. Q.A compound containing carbon, hydrogen, and Oxygen is found to be 40% carbon and 6.7% hydrogen by mass. the molar mass of this

asked by Marty Mc Fly on November 12, 2017
10. ### Chem

i need a bit of help finding out how to do this problem. just tell me how and ill take it from there. Q.A compound containing carbon, hydrogen, and Oxygen is found to be 40% carbon and 6.7% hydrogen by mass. the molar mass of this

asked by ricky bobby martin on November 12, 2017

More Similar Questions