Announcements
Thread starter 11 months ago
#1
Isooctane reacts with an excess of chlorine to form mixture of chlorinated compounds, one of these compunds has 24.6%Carbon 2.56Hydrogen 72.8%Chlorine, calculate molecular formula

so I calculated the empirical and got 1:1.25:1 and the markscheme says multiply that by 4 to give the empricial formula C4H5CL4
but I don't understand why u multiply by 2 to give the molecular formula C8H10CLl8?why ?? how do u get the molecular formula? normally they give the rmm of the molecule and then u have to calculate the empirical mass which for C4H5C4 is 195?
0
11 months ago
#2
(Original post by usernamenew)
Isooctane reacts with an excess of chlorine to form mixture of chlorinated compounds, one of these compunds has 24.6%Carbon 2.56Hydrogen 72.8%Chlorine, calculate molecular formula

so I calculated the empirical and got 1:1.25:1 and the markscheme says multiply that by 4 to give the empricial formula C4H5CL4
but I don't understand why u multiply by 2 to give the molecular formula C8H10CLl8?why ?? how do u get the molecular formula? normally they give the rmm of the molecule and then u have to calculate the empirical mass which for C4H5C4 is 195?
You have not given us all of the required information (like the actual question)
0
Thread starter 11 months ago
#3
(Original post by charco)
You have not given us all of the required information (like the actual question) 0
11 months ago
#4
Isooctane has the formula C8H18
Monochloroisooctane has the formula C8H17Cl

There are two isotopic products one with a Mr of 148 and the other with Mr = 150

The ratio of the two products is given as 1.5 to 1.0 so the average Mr = [(3 x 148)+(2 x 150)]/5 = 148.8

24.6% carbon
2.56% hydrogen
(100 - 24.6-2.56)% chlorine

2.05 C; 2.56 H; 2.05 Cl

C; 1.25H; Cl

Multiply through by 4 to remove fraction.

C4H5Cl4

BUT you are told that it's a chlorinated octane, i.e it has eight carbon atoms, so you must MTB 2 to get eight C atoms

Molecular formula C8H10Cl8
0
Thread starter 11 months ago
#5
(Original post by charco)
Isooctane has the formula C8H18
Monochloroisooctane has the formula C8H17Cl

There are two isotopic products one with a Mr of 148 and the other with Mr = 150

The ratio of the two products is given as 1.5 to 1.0 so the average Mr = [(3 x 148)+(2 x 150)]/5 = 148.8

24.6% carbon
2.56% hydrogen
(100 - 24.6-2.56)% chlorine

2.05 C; 2.56 H; 2.05 Cl

C; 1.25H; Cl

Multiply through by 4 to remove fraction.

C4H5Cl4

BUT you are told that it's a chlorinated octane, i.e it has eight carbon atoms, so you must MTB 2 to get eight C atoms

Molecular formula C8H10Cl8
thank u so much for explaining
0
X

new posts
Latest
My Feed

### Oops, nobody has postedin the last few hours.

Why not re-start the conversation?

see more

### See more of what you like onThe Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

### University open days

• Birmingham City University
Sat, 23 Mar '19
• University of Bolton
Sat, 23 Mar '19
• Harper Adams University
Animals and Veterinary Sciences Open Day Undergraduate
Sat, 23 Mar '19

### Poll

Join the discussion

#### Where do you need more help?

Which Uni should I go to? (112)
17.42%
How successful will I become if I take my planned subjects? (69)
10.73%
How happy will I be if I take this career? (110)
17.11%
How do I achieve my dream Uni placement? (96)
14.93%
What should I study to achieve my dream career? (63)
9.8%
How can I be the best version of myself? (193)
30.02%