K-12 Teaching and Learning From the UNC School of Education

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Daniel Lunk
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In this video, Christine Muth of the North Carolina School of Science and Mathematics demonstrates how to measure pH of a water sample using two types of pH paper.


Christine Muth (00:00)
Hello my name is Christine Muth, I’m from the North Carolina School of Science and Math, and I’m going to demonstrate how to measure pH. A simple way to measure the pH of a sample of water is to use pH paper. pH paper can come in several forms; it could be in a long roll, which is often referred to as pH tape, or it could be in little strips, referred to as pH strips. Also, among the pH strips, some of them are uniform so that the entire strip is essentially the same type of paper and the entire strip is a pH indicator. So a lot of times students assume that you should dunk the paper in and swirl it around or that when you take it out you should wait for the paper to dry before reading off the pH, but in fact, what you want to do is just dunk the pH paper in the water, pull it out immediately, and do your reading immediately before it dries.
So to determine the pH of this sample of water, I’ll simply dunk my pH strip into the water, and then immediately hold it up against my color chart, and looking at this color chart here, it looks like this sample of water has a pH of approximately 5. So I’m just matching the wet part of my pH strip to the color chart. An alternative kind of pH paper, these are color-fast pH strips. They’re a little bit more expensive, but they’re also a little bit more accurate. So what we do with these, they’re not uniform *throughout, they have sort of a plastic kind of strip and then small color blocks at the bottom, which are the actual pH indicator portions. Once again, I would just dunk it into my water sample, and read it off the chart immediately. You actually try to match all three color blocks. This is partly why it’s more accurate because you’re matching three different colors instead of just one, so it’s that combination of colors. So it looks like this pH paper is also reading off this water sample as a pH of 5.0. But another nice feature about this pH paper is that you can read off in increments of .5. So 5.0, 5.5, 6.0. etc. So that’s how you measure the pH of a water sample.