Which digits are significant in ph

Why would we do this? Converting a hydronium ion concentration to a p H value is simple. You would enter 3. First, we multiply this by -1 and get 3.

Next, we examine the number of significant figures. Our experimental number, 3. The reverse process is equally simple. If you are given a p H value of 7. There are only two digits in our original mantissa 7. There is another useful calculation that we can do by combining what we know about p H and expression.

If we define -log [HO — ] as p OH, we can take our expression for K W and take the -log of both sides remember, algebraically you can perform the same operation on both sides of an equation we get:. Which tells us that the values of p H and p OH must always add up to give 14! Thus, if the p H is 3. The simplest way to determine the p H of a solution is to use an electronic p H meter. A p H meter is actually a sensitive millivolt meter that measures the potential across a thin, sensitive glass electrode that is immersed in the solution.

The voltage that develops is a direct function of the p H of the solution and the circuitry is calibrated so that the voltage is directly converted into the equivalent of a p H value. Christy Christy 49 6 6 bronze badges. Also, beware: never in my experience have I differentiated numerical things by whether they were "a scale" or "not a scale". You may have picked up a false notion there somewhere.

So, only the mantissa means anything in terms sig figs. You really need error bars, but I would go with 2. Importantly, note that 4. Show 1 more comment. Active Oldest Votes. Improve this answer. Community Bot 1. Add a comment. Sign up or log in Sign up using Google. Sign up using Facebook.

Sign up using Email and Password. Post as a guest Name. Email Required, but never shown. I have grown to really dislike teaching significant figures over the last few years. In the UK, this is taught in math s class, not chemistry or physics — another thing I prefer! The use of significant figure rules are very generalized. It is like trying to make a rule or a polynomial equation to fit some obscure curve. What really needs to be taught is the precision limits of our instrumentation and lab-ware.

When calculating hydronium concentration from pH, you would get an incorrect answer if you followed rules for sig digs. So that would be 2. Your email address will not be published.