Goals Explain the differences between acids and bases Identify substances as an acid or a base Explain why water is special Describe the pH scale

What is an acid? An acid is an ionic compound that contains a hydrogen ion Hydrogen ion = H+ Hydrogen ion is basically just a proton H has no neutrons and 1 electron, but in an ion, the electron gets removed An acid is a compound that donates (gives up) a proton (H+)

What is a base? A base is an ionic compound that contains a hydroxide ion Hydroxide ion = OH- 1 hydrogen bonded with 1 oxygen and they always stick together As a whole, a hydroxide ion has a -1 charge A base is a compound that accepts (takes on) a proton (H+)

What about water? Water is a special chemical for lots of reasons Water can act as an acid AND a base

What about water? HCl + H2O --> Cl- + H3O+ water acts as a base it accepts a proton to become H3O+ H3O+ is called a HYDRONIUM ion (created when water gets an extra proton)

What about water? H2O + NH3 --> OH- + NH4+ Water acts as an acid It loses a proton to become OH- Water acts different depending on who it is combining with. Sort of like you act different around your friends and around your parents. Water is really H(OH): a hydrogen ion bonded with a hydroxide ion.

How do we know if something is an acid or a base? Look at the chemical formulas, look for H (acid) or OH (base) Look at a chemical reaction, does the compound accept a proton (base) or lose one (acid) Determine the pH of the substance

Acid or Base? NH3 + H2O  NH4+ + OH- Ca(OH)2 + H2CO3  CaCO3 + H2O H2O + CH3COO-  CH3COOH + OH-

What is pH? pH is a number that tells us how acidic or basic a substance is. pH is determined based on the concentration of hydrogen ions or hydroxide ions in the solution. More hydrogen ions = lower pH = acid More hydroxide ions = higher pH = base

What is pH? The pH scale starts at 0 and goes to 14

What is pH? If the pH is from 0-6.9, the substance is an acid The closer to 0, the stronger the acid the closer to 6.9, the weaker the acid If the pH is from 7.1 – 14, the substance is a base The closer to 14, the stronger the base The closer to 7.1, the weaker the base.

What is pH? A pH of 7 is a neutral substance (neither an acid nor a base): WATER, lots of everyday substances We can measure pH using pH strips (special skinny pieces of paper)

There are other ways to determine if something is an acid or a base Indicators these are chemicals that change colors based on their environment Phenolphthalein (Pth) Clear in acids and neutral Turns pink in bases

Litmus paper (red and blue) Turns blue in bases Stays red in acids and neutral substances Blue Turns Red in Acids Stays blue in bases and neutral substances Universal Indicator methyl red, methyl yellow, thymol blue, and bromthymol blue

There are other ways to determine if something is an acid or a base Acids feel clean to the touch and taste sour Bases feel slippery and taste bitter

Rule of Thumb: If you drop a compound into water and it forms hydrogen ions (aka hydronium ions), the compound is an acid. If you drop a compound into water and it forms hydroxide ions, the compound is a base.

Rule of Thumb Ionic compounds will always break down when put into water, this is called IONIZATION (ex. NaCl will break up into Na+ and Cl- in water). Since acids and bases are ionic compounds, they break up in water too.

Agenda Items Part 2 of HW Pkt Part 3: Do NOT do number 3!