5% rule

[Junwei Sun 4I]

When do we use the 5% rule? Do we only use it in acid and base equilibrium questions or any equilibrium questions?

[Hope Hyland 2D]

I think you use it anytime you make an approximation, or assume that x is so small that it's essentially equal to 0.

[Jordan Young 2J]

You use it to check if you can appropriately approximate x to be a small enough that it would effect the initial concentration that much when using the calculation involving K. You will most likely use this when solving equilibrium equations.

[Matthew Tsai 2H]

Also keep in mind x cannot be approximated to zero if it is by itself. So values like x, x^2, etc. would be kept but values like 0.1-x, 0.1+x, etc. can be approximated to 0.1

[Alexandra Bartolome 2H]

I believe when K is less than 10^-3, you can approximate with the 5% rule.

[JohannaPerezH2F]

this rule is used to calculate how accurate your approximation for x is. if it is less than 5% you're good

[LNgo 1G]

I believe you can use it whenever you are calculating K using ICE table just as long as K<10^-3

[kristi le 2F]

The % ionization is the concentration of the molecule in the ionized state divided by the concentration of the molecule in the unionized state. If this is less than 5%, not a significant amount of the molecule ionized compared to the initial concentration.

[Abby Soriano 1J]

Whenever you do any calculations involving ICE tables, you can use the 5% rule to ensure that your approximation that x is small is valid.

[Mariana Fuentes 1L]

I believe you use it when the number is very close to zero that it doesn’t make a difference to the overall answer

[Shivam Rana 1D]

When you cancel out the x and solve. You see if the x value is less than 5% afterwards.

[Simon Dionson 4I]

In my experience, I usually use this rule in weak acid/base equilibria.

[Dina 2k]

is the formula to check to see if the answer is in the 5% range x/[HA]x100% (given its an acid). and isn't this the same formula to find percent deprotonated?

[Pablo 1K]

You use that rule when x is less than 10^-3, its so small it wont change the concentration of a molecule.