Ignoring the change in equilibrium

[kshalbi]

So for equations that don't involve acids and bases we can ignore the chage if it's less than 10^-3 but for ones with acids and bases it's if it's 10^-4?

[kshalbi]

and for the non acid equations can you still ignore the change if K is 1 * 10^-3?

[joannali1027]

Yes because at 1*10^-4, that is when it is appropriate to approximate since the value is very small. I think in terms of regular K values, it is that anything smaller than 10^-3 is considered small enough.

[Daniella Ching 4C]

The safest way (or a double check) to know whether to approximate or not is to see if the change is less than 5% of the original amount present. You can solve the problem by approximation first, then do a quick calculation to make sure that the change falls within 5%.