### Sig figs in pH

Posted:

**Sun Jan 20, 2019 12:02 pm**How do you figure out how many sig figs you are supposed to have in your final answer if being asked to calculate pH?

Created by Dr. Laurence Lavelle

https://lavelle.chem.ucla.edu/forum/

https://lavelle.chem.ucla.edu/forum/viewtopic.php?f=49&t=40275

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Posted: **Sun Jan 20, 2019 12:02 pm**

How do you figure out how many sig figs you are supposed to have in your final answer if being asked to calculate pH?

Posted: **Sun Jan 20, 2019 12:10 pm**

When calculating pH, the whole number doesn't count as a sig fig only the decimal places do. For example, if your concentration of H3O+ has two sig figs, then your pH should have two decimal places.

Posted: **Sun Jan 20, 2019 12:12 pm**

Depending on the significant figures of the data given in the problem, you will have that many sig figs after the decimal for pH. For example say if you were given a K value of two significant figures a potential pH value could be 2.88. You can double check on the website under everything about sig figs.

Posted: **Sun Jan 20, 2019 1:56 pm**

I would say typically when using sig figs in regard to pH having 3 sig figs is standard when presenting your final answer.

Posted: **Sun Jan 20, 2019 2:34 pm**

The number of sig figs in the H3O+ concentration is the how many numbers there should be after the decimal place in the pH value.

Posted: **Sun Jan 20, 2019 2:51 pm**

Dr. Lavelle has 2 links on his website that explain sig figs. It also shows good examples that might be helpful, if you need more clarification.

Posted: **Sun Jan 20, 2019 4:06 pm**

If you're being asked to find pH, make sure to see how many sig figs are in the initial number. The final answer should have the same number of decimal places as the number of sig figs in the initial number.

Posted: **Sun Jan 20, 2019 4:10 pm**

For pH, the sig figs in the final answer are calculated based off the least amount of sig figs in the answer. Then that amount of sig figs is used after the decimal point.