Acids and Bases
From Ibstudy
Contents |
Acids
When dissolved in water, acids give off hydrogen ions (H+). This makes them proton donors.
- An acid is monoprotic if one mole of it gives off one mole of hydrogen ions (HCl, for instance), and diprotic if one mole of it gives of two moles of hydrogen ions.
- Acids can also be triprotic, quadroprotic etc. but you don't really need to know that.
- strong acids dissolve completely in water, while weak acids only partially dissociate.
- Therefore strong acids have more hydrogen ions in the water at a time, and react more quickly.
- With a weak acid, when some of the hydrogen ions react and become something else, more of the acid dissociates to replenish the supply of H+ ions.
- Therefore, a fixed amount (say one mole) of any monoprotic acid can be neutralized by a fixed amount of a base.
- The same amount of a diprotic acid would require twice as much base to neutralize it.
Bases
When dissolved in water, acids give off hydroxide ions (OH-). This makes them proton receivers.
Acids and Bases to know
note: All numbers in the following chart should be in subscript format, but they're not. too bad.
| Type | Name | Formula |
|---|---|---|
| Strong acid | Hydrochloric Acid | HCl |
| Strong acid | Sulphuric Acid | H2SO4 |
| Strong acid | Nitric Acid | HNO3 |
| Weak acid | Ethanoic Acid | HNO3 |
| Weak acid | Carbonic Acid | H2CO3 |
| Strong base | Sodium Hydroxide | NaOH |
| Strong base | Potassium Hydroxide | KOH |
| Strong base | Barium Hydroxide | Ba(OH)2 |
| Weak base | Ammonia | NH3 |
| Weak base | Aminoethane | C2H5NH2 |
Reactions to know
These are pretty straightforward and you can probably figure them out by looking at the formulas that go in, but here are the most common types of reactions that may come up and some example formulas. If you're using Firefox, use the Study Helper to cover up the right side of the formulas and see if you can come up with them yourself. If you're not using Firefox, get with the program.
| Reactants | Products | Example Formula |
|---|---|---|
| Acid + Metal Hydroxide | Salt + Water | HCl(aq) + MgOH → MgCl + H2O |
| Acid + Metal | Salt + Hydrogen | H2SO4(aq) + 2Na → Na2SO4 + H2 |
| Acid + Metal Carbonate | Salt + Water + Carbon Dioxide | 2HNO3 + K2CO3 → 2KNO3 + H2O + CO2 |
Measuring acidity
the pH Scale
Acidity is measured on a scale of pH (stands for the power of Hydrogen), from 0 to 14, with 0 being a really, really, freaking strong acid and 14 being a base potent enough to dissolve all of the lipids in your body real quick-like.
The pH of a solution is equal to the negative magnitude of the concentration of hydrogen ions in a solution.
- If a solution has a concentration of 10^-2 M of hydrogen ions, it has a pH of 2.
- Mathematically speaking, the pH is therefore equal to the negative log in base ten of the concentration of hydrogen ions.
pH Meters
pH meters measure the conductivity of a solution to determine its acidity.
Acidic solutions contain extra H+ ions, so they conduct electricity better. Conductivity increases as pH decreases
Indicators
Indicator solutions and indicator paper (paper soaked in indicator solution) are used to create a visual indication of the pH of a solution.
You have to know four of them:
| Indicator | Color in Acid | Color in neutral solution | Color in Base |
|---|---|---|---|
| phenolphthalein | clear | clear | fuchsia |
| methyl orange | red | yellow | yellow |
| litmus | red | purple | blue |
Universal indicator provides a range of colors, each corresponding to certain pH.
Here's an excellent graph of the three indicators and their colors.
