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AICE Chemistry

AICE Chemistry . Acids and Bases. Acids. These are chemical compounds that can be identified because they start with the element Hydrogen. They have the generic formula “HX”. . The “X” part can be either a non-metal or a polyatomic. If the “X” is a non-metal, we have a binary acid.

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AICE Chemistry

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  1. AICE Chemistry Acids and Bases

  2. Acids • These are chemical compounds that can be identified because they start with the element Hydrogen. • They have the generic formula “HX”. • The “X” part can be either a non-metal or a polyatomic. • If the “X” is a non-metal, we have a binary acid. • If the “X” is a polyatomic, we have an oxy-acid.

  3. Examples Binary Acids Oxy-Acids HNO3 H2SO4 HC2H3O2 H3PO4 • HCl • HBr • H2S

  4. Acid Names • Binary acids are named according to the format “hydro _______ ic acid” • The prefix “hydro” means binary acid. • All that you need in the space is usually the root of the non-metal’s name. • Oxy-acids are named according to the format “_________-ic acid. • There is no “hydro” here – these are not binary acids. • All that you need in the space is usually the root of the polyatomic’s name.

  5. Examples Binary Acids Oxy-acids HNO3 = nitric acid H2SO4 = sulfuric acid ( again, a bit of an exception for the same reason noted in the binary name example) HC2H3O2 = acetic acid H3PO4 = phosphoric acid (another exception) • HCl = hydrochloric acid • HBr = hydrobromic acid • H2S = hydrosulfuric acid (this one is a bit of an exception – we use the full name of sulfur because it sounds better than “hydrosulfic” acid)

  6. Some Related Vocabulary • We will eventually discuss the chemical behavior associated with acids losing the hydrogen atoms attached to the “X” part. • From the formulas, you can see that different acids have different numbers of H atoms attached to that “X”. • Since an H atom is nothing more than a proton (and a bonding electron) , we have: • Monoprotic acids – that have only 1 H atom attached to the “X”. • Diprotic acids – that have 2 H atoms attached to the “X”. • Triprotic acids – that have 3 atoms attached to the “X”.

  7. Examples and Practice • H2CrO4 • HI • H2CO3 • HF • H3PO4 • H2Cr2O7 • H2SO4 • Describe each of the acids to the left in terms of the vocabulary already covered so far.

  8. Chemical Behaviors • Acids react with metal carbonates to produce aqueous “salt”, gaseous carbon dioxide, and water. • This is the pattern for both binary and oxy-acids. • Note that a bicarbonate will yield the same results. • Acids react with metals to produce hydrogen (diatomic) and an aqueous “salt”. • Definition – a “salt” is simply an ionic compound produced during a reaction involving an acid. It contains the metal cation and the anion of the acid (the “X” part). • Note – there are some very significant exceptions to this pattern.

  9. Write Equations for the Following: • Aqueous hydrobromic acid reacts with solid potassium carbonate. • Aqueous acetic acid reacts with solid sodium bicarbonate. • Several pieces of zinc are added to a flask containing aqueous nitric acid. • A piece of magnesium ribbon is added to a beaker of sulfuric acid.

  10. Ionization – Another Chemical Behavior • Ionization is the term given to the reaction that occurs when an acid is dissolved in water. • Unlike the dissolving of an ionic compound – a physical change – ionization is actually a chemical reaction between the acid and the water. • In the reaction, the H atom proton leaves the “X” part and attaches itself to the two lone pairs of electrons on the water molecule. • The product particle has the formula H3O+1 and is called the hydronium ion. • The other product particle is an anion of the “X” part. It has a charge because it keeps the H atom’s electron when the H leaves.

  11. Look at the Equations • Given: Hydrochloric acid is dissolved in water • Even though the given says “dissolved” in water, since this is an acid we have to realize that this is actually a chemical reaction. • So it is written as: HCl + H2O  H3O+ + Cl-

  12. Another Example: • Nitric acid is dissolved in water: • The fact that this is an oxy-acid does not change the format of the reaction and equation. The H atom is leaves the nitrate and attaches to the water forming hydronium. The nitrate ion is the other product. HNO3 + H2O  H3O+ + NO3-1

  13. What about Diprotic Acids? • These will be a bit more complicated. • The key to these is to remember that in an ionization, one H atom leaves the acid, bonds with the water to form hydronium, and the remaining particle is “one more negative” than it was before the ionization. • What you will see is that a diprotic acid will undergo two separate ionizations. • Likewise, a triprotic acid will undergo three separate ionizations.

  14. Consider Sulfuric Acid • Sulfuric acid is H2SO4 and is obviously diprotic. • Its two separate ionizations are presented below. 1st Ionization: H2SO4 + H2O  H3O+ + HSO4-1 2nd Ionization HSO4-1 + H2O  H3O+ + SO4-2

  15. A Quick Check: • Write the set of ionizations that occur in phosphoric acid.

  16. Stoich VIII for Acids • This is actually easier for acids than it was in the Equilibrium unit. • Your typical focus is going to be on calculating the concentration of hydronium in the solution. • What makes this relatively easy is that ionization is always a one-to-one ratio.

  17. An Example: • Consider the ionization of HCl from an earlier slide: HCl+ H2O  H3O+ + Cl- • As you can see, the ratio of HCl to H3O+ is one-to-one. (coefficients) • Therefore, whatever the concentration of the HCl solution is, the [H3O+] will be the same – all of the HCl actually becomes H3O+ .

  18. What That Means: • If we are told that the [HCl] is 0.200-molar , then the [H3O+] is the same thing – 0.200 M. • For the time being (it gets a bit more complicated when we learn about weak acid equilibrium) … • Whatever the concentration of the acid solution is – we will simply state that the concentration of hydronium is simply the same thing.

  19. Why the Concern? • We will need to be able to specify the concentration of H3O+ in order to calculate the pH of an acid (and eventually a base) solution.

  20. pH • pH is a numerical scale that is used to describe the relative acidity of a given solution. • Important to keep in mind that pH is calculated using the [H3O+] , but pH is NOT the actual concentration of anything. • The pH scale was developed in order to facilitate greater understanding – the general public was essentially lost when a discussion included a concentration – measured in moles/liter

  21. Think about it… • You are trying to communicate information about the relative acidity of a solution and you tell the listener that the system is 0.0010-molar. • And they think that you are talking about teeth. • But, if you tell the listener that the solution has a pH = 3 , they are far more comfortable – even though they probably do not have enough of a Math background to understand how pH is calculated.

  22. Comparing The solution is 0.0010-molar The pH of the solution is 3

  23. The pH Equation pH = - log [H3O+] Which is: the pH of solution is the opposite of the base10 log of the concentration of the hydronium in the solution.

  24. The pH Scale • This is a numerical scale that presents the relative acidities and basicities of acid and base solutions. • It commonly runs from 0 to 14 . • Next slide show the structure of the scale.

  25. Visual of the pH Scale

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