# Chemistry- empirical formula

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Thread starter 10 months ago
#1
a compound of boron and chlorine has a relative molecular mass of 163.6 and contains 13.2% of boron by mass. Calculate the molecular formula of this compound?
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10 months ago
#2
(Original post by Meyalio)
a compound of boron and chlorine has a relative molecular mass of 163.6 and contains 13.2% of boron by mass. Calculate the molecular formula of this compound?
If 13.2% is boron, how much chlorine is there?
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10 months ago
#3
try here it may help a bit

https://www.science-revision.co.uk/m...20formula.html
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10 months ago
#4
(Original post by Meyalio)
a compound of boron and chlorine has a relative molecular mass of 163.6 and contains 13.2% of boron by mass. Calculate the molecular formula of this compound?
Step 1:
Find out the percentage of chlorine.
Hint: The question tells you the compound is made of boron of chlorine. The percentage of boron is given.

Step 2:
Find out the ratio of boron to chlorine.
Hint: Use the formula Moles = Mass / Mr
Remember, you can use the percentage value as the mass value.

Step 3:
Use the ratio and substitute it in the compound.

E.g. If your ratio of boron to chlorine was 2:3, write B2Cl3
*THIS IS NOT THE CORRECT ANSWER.

Step 4:
Find the Mr of the compound.

E.G.
B -> 10.8
Cl -> 35.5

B2Cl3
(10.8 x 2) + (35.5 x 3) = 128.1

*THIS IS NOT THE CORRECT ANSWER.

Step 5:
Divide the relative atomic mass given in the question by the answer you found in Step 4. This will give you the factor you need to multiply by the answer you got in Step 3 to find the molecular formula.

E.G.
163.6 / 128.1 = 1.277 = 1.3

B2Cl3

B -> 2 x 1.3 = 2.6
Cl -> 3 x 1.3 = 3.9

B2.6Cl3.9

*THIS IS NOT THE CORRECT ANSWER.

As I chose a random ratio to explain how to do the question, my answer does look rather weird. I hope it does help you with how to do the question, though!
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Thread starter 10 months ago
#5
(Original post by 5hyl33n)
Step 1:
Find out the percentage of chlorine.
Hint: The question tells you the compound is made of boron of chlorine. The percentage of boron is given.

Step 2:
Find out the ratio of boron to chlorine.
Hint: Use the formula Moles = Mass / Mr
Remember, you can use the percentage value as the mass value.

Step 3:
Use the ratio and substitute it in the compound.

E.g. If your ratio of boron to chlorine was 2:3, write B2Cl3
*THIS IS NOT THE CORRECT ANSWER.

Step 4:
Find the Mr of the compound.

E.G.
B -> 10.8
Cl -> 35.5

B2Cl3
(10.8 x 2) + (35.5 x 3) = 128.1

*THIS IS NOT THE CORRECT ANSWER.

Step 5:
Divide the relative atomic mass given in the question by the answer you found in Step 4. This will give you the factor you need to multiply by the answer you got in Step 3 to find the molecular formula.

E.G.
163.6 / 128.1 = 1.277 = 1.3

B2Cl3

B -> 2 x 1.3 = 2.6
Cl -> 3 x 1.3 = 3.9

B2.6Cl3.9

*THIS IS NOT THE CORRECT ANSWER.

As I chose a random ratio to explain how to do the question, my answer does look rather weird. I hope it does help you with how to do the question, though!
Thank you so much for your help this actually made sense to me. Many many thanks. I am so relieved.
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10 months ago
#6
(Original post by Meyalio)
Thank you so much for your help this actually made sense to me. Many many thanks. I am so relieved.
No problem. What did you get as your answer?
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