## 5% Rule

JesseAuLec1Dis1G
Posts: 52
Joined: Mon Jun 17, 2019 7:23 am

### 5% Rule

If I make the assumption because K is less than 10^-3, but the x value is less than 5% do I have to go back and use the quadratic formula to calculate x?

Shimei_2F
Posts: 100
Joined: Fri Aug 09, 2019 12:17 am

### Re: 5% Rule

If X is less than 5% of the initial, you should be on the right track!

Gerald Bernal1I
Posts: 102
Joined: Thu Jul 11, 2019 12:16 am

### Re: 5% Rule

The protonation being less than 5% guarantees that the assumption to neglect X because the change is so small so you should not have to use the quadratic.

Dan M -3E
Posts: 101
Joined: Wed Sep 18, 2019 12:19 am

### Re: 5% Rule

Yeah, it being less than 5% just means u can neglect it the x that is subtracted when calculating the Kc using x

Sara Richmond 2K
Posts: 110
Joined: Fri Aug 30, 2019 12:16 am

### Re: 5% Rule

JesseAuLec1Dis1G wrote:If I make the assumption because K is less than 10^-3, but the x value is less than 5% do I have to go back and use the quadratic formula to calculate x?

If the value is less than 5% you are good to go. If the value is more than 5% you would need to go back and use the quadratic formula.

BCaballero_4F
Posts: 94
Joined: Wed Nov 14, 2018 12:22 am

### Re: 5% Rule

You go back and use the quadratic formula only if it is more than 5%

Michelle N - 2C
Posts: 117
Joined: Wed Sep 18, 2019 12:19 am

### Re: 5% Rule

JesseAuLec1Dis1G wrote:If I make the assumption because K is less than 10^-3, but the x value is less than 5% do I have to go back and use the quadratic formula to calculate x?

I believe the 5% rule applies to when we are to ignore the -x in the problem or not, because what I remembered was that as long as the answer is within the 5% rule, then our approximation is valid.

Ellen Amico 2L
Posts: 101
Joined: Thu Sep 19, 2019 12:16 am

### Re: 5% Rule

If the % ionization is less than 5%, then we can use assumption and get rid of the x in the denominator since the initial and equilibrium concentrations will be very similar.

ThomasNguyen_Dis1H
Posts: 102
Joined: Fri Aug 30, 2019 12:17 am

### Re: 5% Rule

No only when it is more than 5% then you have to do quadratic

Kylie Lim 4G
Posts: 110
Joined: Sat Aug 17, 2019 12:15 am

### Re: 5% Rule

you only need to go back and use the quadratic formula if you check X and it is more than 5% of the initial value