# Percentage Yeild - check answer?

1. Sep 19, 2008

### a.a

1. The problem statement, all variables and given/known data
The direct reaction of silicon with Cl_2 the yield of SiCl4 is 50%. How many grams of SiCl4 are obtained in the reaction of 2.8 g of silicon with excess chlorine?

2. Relevant equations
Si= 28.0855g
SiCl4= 169.8963g
Si + 2Cl2 --> SiCl4

3. The attempt at a solution
2.8g Si = (84.94815 g SiCl4/28.0855 g Si)* 2.8g Si
= 8.468 g SiCl4
= 8.5 SiCl4

2. Sep 19, 2008

### Staff: Mentor

This is obviously wrong - perhaps just what you wrote is wrong, as the final number looks OK. But for sure 2.8 g Si doesn't equal 8.468 g SiCl4.

However - where is the yield percentage used? Have you forgot?

3. Sep 19, 2008

### a.a

sorri, the way i wrote is is wrong, i ment to say that 2.8 Si produces 8.468 g SiCl_4
i used the percentage yeild in that i said 84.94815 g SiCl4 rather than 169.8963g

4. Sep 19, 2008

### Staff: Mentor

Use precentage as the last step, after you calculate correct stoichiometric amount. Numbers look OK.

5. Sep 19, 2008

### a.a

do we still arive at the same answer though?

6. Sep 19, 2008

### Staff: Mentor

Yes. That's why I wrote that numbers look OK.