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High school biology
Course: High school biology > Unit 1
Lesson 4: pH, acids, and basespH, acids, and bases review
Key terms
| Term | Meaning |
|---|---|
| pH | The measure of the hydrogen ion (H+) concentration in a solution |
| Acid | Solution with a higher concentration of hydrogen ions than pure water |
| Base | Solution with a lower concentration of hydrogen ions than pure water |
Reading the pH scale
The pH scale is used to rank solutions in terms of how acidic or how basic they are. It indicates the concentration of hydrogen ions (H+) and hydroxide ions (OH-) in a solution. These ion concentrations are equal in pure water, which has a pH of 7.
This pH value of 7 is important because it indicates a neutral solution. All other substances are compared to this neutral point. Any solution that has a pH of less than 7 is considered acidic, and anything above a pH of 7 is basic.
Common mistakes and misconceptions
- Acids are not always dangerous. Acids sometimes have a bad reputation for being dangerous, but there are plenty of acidic substances that are useful (and even tasty!). For example, orange juice and coffee are acidic substances. In addition, though there are a few acids that you want to avoid handling (ie: hydrofluoric acid), don’t be fooled: strong bases can be damaging as well.
- Lower pH number means stronger acid, higher pH number means stronger base. It can be a little confusing, but the lower the pH of a substance is, the stronger of an acid it is. Sometimes it is more helpful to think that the further away from neutral a substance is, the stronger it is in either the acidic or basic direction.
- Acids and bases are not only important in chemistry. Although you may go into more detail learning about them in your chemistry class, acids and bases are extremely important to living things! In fact, most enzymes work best at a specific pH. For example, the enzyme pepsin is necessary for the digestion of proteins in the stomach, but it only functions at a very low pH. Therefore, it is important for the body to maintain an acidic environment in the stomach to make sure food gets digested well.
Want to join the conversation?
If the pH scale is 0-14, how can you have acids that are ranked at -6, -10, -18, -32, etc. pH?(28 votes)
Hi, the answer lies in the way the pH is calculated. Although this may seem a little advanced. The pH is calculated by taking the -log of the concentration of a certain ion in a solution. In scientific notation, for example, if the concentration of this ion is 1x10^-10 mol/L, then the pH would be 10! Therefore, you can work backwards to see that if an acid had a concentration of 1x10^2 mol/L, then its pH would be -2! so basically negative pH indicates that the acid is very strong. (Just copy and pasted Aeshons comment so everyone could see. This is not my original comment. Aeshon gets all the credit)(9 votes)
I thought that bleach was acidic because of the way it turns whatever it touches white?(19 votes)
I think that's the chemical reaction of the bleach when it reacts to clothing. Bleach is a base because it doesn't have anything that is acid.(14 votes)
is lemon juice more acidic than bleach(8 votes)- since every number you go up the scale the baseity (?) gets 10 times stronger. So if lemon juice has a pH of 2 and bleach has a pH of 13 that means lemon juice is 100,000,000,000 times more acidic than bleach.(7 votes)
Is there a reason alkaline batteries have the word "alkaline" in them? Because I saw on the scale battery acid is very acidic, but in the video it said alkaline was a term for basic solutions (1:25)(9 votes)- Maybe instead of having a acidic acid in the battery maybe it has a alkaline substance.(4 votes)
I have an interesting question: Do medicine pill or tablets even have a pH of acidic or basic?(8 votes)
It would have to, I'm pretty sure all chemicals, liquids, foods, and medicines have a pH.(3 votes)
it was said that an Acidic solution is one with a higher concentration of hydrogen ion than pure water.
what does this mean?
does it mean that if the concentration of H ion in a solution is higher than the concentration of H ion in pure water then that substance is acidic?(5 votes)
Yes! The Hydrogen (or hydronium) ion concentration of pure water at 25 degrees Celsius is 10^-7 (if you're not sure where this came from, Khan Academy has some videos on it). If the Hydrogen concentration of a solution is higher than 10^-7, the solution is said to be acidic.(6 votes)
- It is said above that " Most enzymes work best at a specific pH" Why is it so?(5 votes)
- It's because enzymes are sensitive to pH. For an enzyme to work and for a product, its active site must combine with the substrate to for an enzyme-substrate complex as in the induced fit model. However, in conditions that are not optimal, such as when an enzyme is placed in a solution with a pH value that's outside an enzyme's optimum, it can become denatured. In this, the enzyme loses its 3D shape and its ability to react with the substrate to form a product. This is why enzymes work best at a specific pH. Hope this helps.(3 votes)
Lower pH number means stronger acid, higher pH number means stronger base.
Why?
On the scale, it seems it is exactly like that.(4 votes)
It is this way because the scientist that first made the scale put it this way. According to Wikipedia The concept of pH was first introduced by the Danish chemist Søren Peder Lauritz Sørensen at the Carlsberg Laboratory in 1909 and revised to the modern pH in 1924 to accommodate definitions and measurements in terms of electrochemical cells. Hope this helps :)(4 votes)
What is considered a weak acid1:58pm.(4 votes)- I have two questions
1. is it possible for there to be a base with the properties of an acid, or an acid with the properties of a base?
2. Can a substance be both an acid and a base? And if so where would it be on the pH scale?(3 votes)- 1. On a molecular scale, acids will always donate their protons and bases will always accept protons and form hydroxide ions. However, on a macroscopic scale, each can be corrosive and dangerous, if this is what you mean.
2. In fact, yes! An example of such a substance is water, which will act like a base if it reacts with an acid, and will act like an acid should it react with a base. From my knowledge, they do not have specific charges.
Does this help?(5 votes)
1:25