Chapter 10 Acids and bases

Identifying features of acid Sour tastes ( ex. lemon juice, vinegar) Conducts electricity when in liquid (electrolyte) React with a base to form water & a salt (neutralization rxn) A salt is the ionic product of an acid base rxn

Identifying features of acid Acids react with certain metals to form H 2 gas. Look at table J. All metals that are above Hydrogen will react with it, but those below wont. Cause indicators to change colors (more on this later)

Bases Bitter taste (bleach, ammonia, soap) Slippery or soapy feeling Conduct electricity in liquid (electrolyte) React with acids to form water and a salt Cause indicators to change colors (more on this later)

What makes an acid an acid Scientists had known for a long time common features of acids, but they didn’t know why an acid displayed those features What was it that made an acid an acid.

Arrhenius Svante Arrhenius proposed that an acid is any substance that when mixed with water will give off a Hydrogen ion. HCl ----  H + & Cl - HNO 2 --  H + & NO 2 - H 2 SO 4  2H + & SO 4 2-

Not everything with a hydrogen is an acid Methane CH 4 & Sugar C 6 H 12 O 6 are molecules with a hydrogen that are not acids. & Sugar C 6 H 12 O 6 are molecules with a hydrogen that are not acids. Molecules with H are only acids if the molecule is ionic, but if the molecule is covalent the H is not released in liquid.

So what makes a hydrogen acidic? When a H + ion is in water it cannot remain there alone. It will quickly react with water to form H This new molecule is called a hydronium ion. This new molecule is called a hydronium ion. So all the acidic substances act the way they do, bc of their Hydronium ions.

Bases According to the Arrhenius theory a base is any substance that increases the amount of OH - (hydroxide) ions in water. NaOH  Na + & OH - NaOH  Na + & OH - KOH  K + & OH - KOH  K + & OH - Ca(OH) 2  Ca +2 & 2OH - Ca(OH) 2  Ca +2 & 2OH - The properties of a base is because of the OH

Exception NH3 (ammonia) is classified as a base even though it lacks OH. But upon closer examination we find NH3 does create OH - ions. NH 3 + H 2 O  NH 4 + & OH -

Table K & L On your reference table the common acids and bases you need to know for the regents are listed.

Strength of acids and bases Hydrocloric acid --- very dangerous Citric acid ----Found in plants Boric acid--- used in eye washes

Strenghts of acids A very strong acid will have all of its Hydrogen’s leave the compound and enter the water A very weak acid will only have a few of its H’s leave the compound and enter the water

Reactions As we saw on from table J acids react with most metals to release H 2 gas. We also have a Neutralization reaction. This is when an acid and base react to balance each other out.

Neutralization reactions HCl + NaOH  H 2 O + NaCl Acid + Base  Water + salt

Neutralization reaction The H of acid combines with the OH of base to create H 2 O The left over molecules combine to make a salt.

Neutralization reaction HNO3 + KOH  ? Acid + Base  Water & salt H & OH combine to make H 2 O NO 3 & K combine as the salt = KNO 3

Neutralization reactions HNO3 + NaOH HCl + KOH H3PO4 + 3 NaOH H3PO4 + 3 NaOH

PH Scale In chemistry we measure the concentration of an acid or base on a scale of 1-14 This is called the PH scale.

On the PH scale 0-7 is acidic. The lower the number the more acidic. (More H + ) 7-14 is basic. The higher the number the more basic (more OH - ) 7 is neutral. (Pure water)

PH Scale If bananas have a PH of about 5 & milk is about 6, which is more acidic? Ammonia has a PH of 11, soap has a PH of 12. Which has more OH - Ions

Indicator An indicator is a chemical that will change colors in order when placed in a certain PH. They are used to indicate what the PH of a liquid is.

PH Scale Each number moved on the PH scale is increased 10 times more acidic, or basic. Example if HCl is a ph of 1 And Acetic acid is a ph of 2 How much more acidic is HCl then acetic acid?

PH If 1 number on the scale is 10 times more acidic (or basic) Then 2 numbers is 100 times more acidic (or basic) And 3 numbers is 1000 times more

Example How much more basic is a solution of PH 10 then a solution of PH 8? What about PH 9? PH 7? How much more acidic is ph 6 then 7?

Example A truck carrying nitric acid overturns and spills its content in a neerby lake, that had a PH of 8. After the spill the lake is 1000 times more acidic. What is the new PH?

Titration In a neutralization reaction there must be a 1:1 ratio of H + to OH - Using this knowledge we can determine the concentration of an acid by only knowing the concentration of the base it reacted with.

Titration For example If I have 1 L of 1 molarity acid I will need 1 L of 1 molarity base to cancel it out. What about if I only had 2 Molarity base, how much would I need to cancel out the acid?

Titration I would only need half a liter of the 2 Molarity base to cancel out all the acid.

Titration The formula for titration is found on your reference table. It is M a * V a = M b * V b This mean Molarity of acid X volume of acid = Molarity of base X volume of base

Titration What is the concentration of sulfuric acid if 50 mL of.25 Molarity KOH are needed to neutralize 20 mL of the acid? M a * V a = M b * V b X * (20) =(.25) * (50) X is the Molarity of sulfuric acid

Bronsted Lowry theory There is another theory of acids & bases besides Arrhenious called the Bronsted Lowry theory. The regents just calls it the alternative theory.

Bronsted Lowry theory According to this theory an acid is anything which is a H + donor And a base is anything that accepts H +