{"page":"\n\n
\n
\n
\n
\n
\n\nVideo\n
\n

\nHydrogen Ions and Acidity\n

\n
\n
\nGet Free Access for 10 Days!\n
\n
\n
\n
\n
\n
×
\n\n\n
\n\nPublisher:\n\nTeacher's Pet\n\n\n
\n
\nLearn about the basis of the pH scale and how to do some pH and pOH calculations in this video! Transcript _____________________ When water gains a hydrogen ion, it becomes hydronium, H3O+. When water loses a hydrogen it becomes...\nLearn about the basis of the pH scale and how to do some pH and pOH calculations in this video! Transcript _____________________ When water gains a hydrogen ion, it becomes hydronium, H3O+. When water loses a hydrogen it becomes Hydroxide ion OH-. Water will self ionize, meaning one molecule will break apart giving a hydrogen to another water molecule and leaving hydroxide behind. This occurs only to a very, very small extent. It would be more accurate to draw the double arrow so that the forward reaction was much smaller than the reverse. Most water molecules will stay as water molecules and not separate. The concentration of hydronium is 1 x 10^-7 which is a very tiny amount. the concentration of hydroxide ion is the same amount, because they came from the splitting of water. water is a neutral compound because the concentration of hydrogen and hydroxide are equal. If it’s unequal, the solution will be either acidic or basic. If the concentration of hydrogen ions is increased, the concentration of hydroxide will decrease, and it’s an acidic solution. If the concentration of hydrogen is decreased then the concentration of hydroxide increases, and it’s a basic solution. Basic solutions are also known as alkaline solutions. Since the concentration of hydrogen and hydroxide ions is inverse, we can calculate their constant, which is always 1 x 10 to the negative 14th power. Take a look at this table. As the concentration of hydrogen ion decreases, the hydroxide increases, but their product is always 1 x 10^-14. If you look at the exponent on the hydrogen ion concentration you’ll notice that the numbers go from 0 to -14. Sorenson the biochemist knew that if you take the log of an exponent, you get the exponent, but he also liked the look of positive numbers. so he came up with this formula: pH=-log[H+] on the pH scale, acids have a pH below 7 and bases have a pH above 7. 7 is neutral. the pH scale measures the power of hydrogen, the pOH scale measures the power of hydroxide. Since they have an inverse relationship, the pOH scale has numbers in the opposite direction. So an acid with a pH of 3 has a pOH of 11. the pOH can be calculated from a concentration of hydroxide ion in the same manner as the pH. pOH equals the negative log of the hydroxide ion concentration.the pH plus pOH will always equal 14. so you can easily find the pOH if you know the pH and vice versa. Now significant figures in the pH and pOH scales are a little bit different than your usual numbers. Because the digits before the decimal denote the exponent, it’s only the numbers after the decimal that count as significant figures. so the pH of 6.725 has 3 significant figures and 10.37 has 2 sig figs. let’s try a calculation. What is the [H+] of a solution with pH = 8.00? We know that pH = negative log of the concentration of hydrogen. But, we need to rearrange this equation to get concentration of hydrogen ion by itself. we need to divide both sides by negative log. dividing by log is called inverse log or antilog. On your calculator it probably looks like 10^x. so our equation is antilog times negative pH equals concentration of hydrogen. let’s plug in the pH we were given, and calculate. We get 6.3 x 10^-9 molar which has two significant figures, and M, molar, is the unit of concentration. now lets try one with a couple of steps. what is the pH of a solution with a [OH-] = 2.0 x 10^-10? we know that pOH = -log[OH-] so we can plug in our concentration to find pOH which is 9.70. We also know that pH and pOH always add up to 14, so if we subtract 9.7 from 14 we get 4.3 which is our pH. so this solution is acidic. a quick way to test the pH of a substance is to use indicators. they will change color in the presence of an acid or a base. They aren’t always the most reliable source, however, because temperature can distort their color, and if the substance your are testing already has a color to it, the indicator color will be difficult to see. a pH probe will be the most accurate tool for measuring pH.\n
\n
\n\n
\n
\n
\n
\n

Resource Details

\n
\n
\n
\n
Curator Rating
\n
\n
\n
\n
\n
\n
Educator Rating
Not yet Rated
\n
\n
\n
\n
\n
Grade
9th - 11th
\n
\n
\n
\n
\n
Subjects
All Subjects
\n
\n
\n
\n
\n
Media Type
Instructional Videos
\n
\n
\n
\n
\n
Source:
\n
\n
\n
\n
\n
\n
Date
\n
2015
\n
\n
\n
\n
\n\n\n
\n
\n
\n
\n
Audiences
For Teacher Use
2 more...
\n
\n
\n
\n
\n\n
\n
\n
\n
\n
\n

Educator Ratings

\n
\n
\n
\n
\n
\n\nShow resource details\n
\n
\n\" data-title=\"Get Full Access\" data-container=\"body\" rel=\"popover\" tabindex=\"0\" aria-label=\"Play video: Hydrogen Ions and Acidity\" href=\"/subscription/new\">\"Hydrogen\n\n
\n
\n
\n
\n
\n\n"}