We'll go over all the formulas you need to find pH, pOH, acid concentration and
base concentration. Hello everyone I'm Melissa Maribel your personal tutor and
let's go over two potential test questions. In question 1, we are given the
concentration of acid and asked to find the pH, pOH and base concentration to
find the pH we will use the pH formula and plug in the given acid concentration.
Alright, important significant figure note, pH and
pOH have specific significant figure rules when you are given an acid or base
concentration the amount of sig figs you have will be the amount of decimal
places the pH and pOH should be rounded to, this is why we get 3.39 as our pH and
note our pOH will also have two decimal places. Since we just found the pH we can
use this formula and plug in pH to find pOH subtract both sides by three point
three nine and our pOH is ten point six one since
we just found pOH and we are now finding the concentration of base we can use
this formula and plug in the pOH. Plugging this into your calculator make
sure to press 2nd log and then put the exponent of negative ten point six one.
Round to two sig figs since our initial acid concentration had only two sig figs.
This gives us two point five times ten to the negative 11th and our units are
in molarity since concentration is measured in molarity. In question two we
are given the pH and asked to find our acid and base concentrations and the pOH
starting with part A since we are given the pH we can use this formula and solve
for that acid concentration so press 2nd log on your calculator then input the
exponent of negative 8.5 and we get this as our acid concentration. Significant
figure note when we're going from pH to acid concentration
the number of decimal places for the pH tells you how many sig figs to round to
this is why our acid concentration only has one sig fig. Part B to find our base
concentration we will use this formula and plug in the acid concentration we've
just found divide both sides and we will get this as our base concentration
rounded to one sig fig. Part C there are two formulas we can use to find pOH in
this case here's the first formula we'll plug in the base concentration to get
this as our pOH the second formula we could have used instead was this one and
we can plug in our pH subtract both sides by 8.5 and we would get the same
value. Now here's a summary of when to use each formula when going from your
acid concentration to pH use this formula. Going the opposite way from pH
to acid concentration use this. Now when you're going from your base
concentration to pOH use this formula. Going the opposite way from pOH to base
concentration use this if you are given the pH and asked to find pOH or going
from pOH to pH use this formula. Going from acid concentration to your base
concentration or vice versa base concentration to acid concentration use
this. If you want to cut your study time in half I created detailed notes on
everything you need to know on acids and bases you can find that in the
description box below and make sure to check out this other helpful video and
remember stay determined you can do this!