Reaction Types Flashcards Preview

AP Chemistry > Reaction Types > Flashcards

Flashcards in Reaction Types Deck (76)
Loading flashcards...
1
Define and give a general reaction for:

Brønsted-Lowry acid

Brønsted-Lowry acid is any species capable of donating a proton to the solution and results in an increase in hydronium ion concentration, hence a decrease in pH.  

Note: This is the definition that the AP Chemistry test uses for any acid in general.

Example acid reaction:

HA + H2O ⇒ A- + H3O+

2
Define and give a general reaction for:

Brønsted-Lowry base

A Brønsted-Lowry base is any species capable of accepting a proton from the solution and results in an increase in hydroxide ion concentration, hence an increase in pH.

Note: This is the definition that the AP Chemistry exam uses for any general base.

Example base reaction:

NH3 + H2O ⇒ NH4+ + OH-

3

Is CH3COOH an acid or a base?

CH3COOH is an acid. It loses a proton to solution.

Acid Equation:

CH3COOH + H2O ⇒
CH3COO- + H3O+

4

Is NH3 an acid or a base?

NH3 is a base. It accepts a proton (or creates an OH-) in solution.

Base Reaction:

NH3 + H2O ⇒ NH4+ + OH-

5
Define and give an example of:

strong acid

A strong acid is one which dissociates completely in solution.

For a monoprotic acid (one proton per molecule), each mole of acid in solution results in one mole of protons in solution as well.

Ex: HCl is a classic strong acid (monoprotic).

6
Define and give an example of:

strong base

A strong base is one which dissociates completely in solution.

For a monobasic compound (one hydroxide per molecule), each mole of base in solution results in one mole of hydroxide ions in solution as well.

Ex: NaOH is a classic strong base (monobasic).

7
Place these in order of increasing acid strength:

H2O; NH3; HF; CH4

CH4 < NH3 < H2O < HF

Acidity, in general, is a measure of how easily that substance will donate a proton into solution.

8
Why is this the ranking of increasing acid strength?

CH4 < NH3 < H2O < HF

CH4 < NH3 < H2O < HF

These molecules are an increasing series going from left to right across the second row of the Periodic Table. Traveling left to right across the Periodic Table, acidity always increases.

The reason for this is polarity. Chemically, these acids are: a hydrogen atom bound to a central atom. As the central atom becomes more electronegative, the bonds with hydrogen become more polar. More polar bonds are easier to dissociate in aqueous solution. Hence, the more electronegative the central atom, the more easily it donates protons, and the more acidic it is.

9
Place these in order of increasing acid strength:

HCl; HF; HI; HBr

HF < HCl < HBr < HI

Recall: acid strength is determined by how easily the substance will donate a proton into solution.

10
Why is this the order of increasing acid strength?

HF < HCl < HBr < HI

HF < HCl < HBr < HI

These molecules are a series going down a column of the Periodic Table. As you travel down a column in the Periodic Table, acidity increases. 

The reason for this is atomic size. Larger atoms can carry negative charges more easily, so the I- ion is more stable than the F- ion. The more stable the conjugate base, the stronger the acid.

11

Please list six common strong acids.

  1. HI (Hydrogen Iodide)
  2. HBr (Hydrogen bromide)
  3. HCl (Hydrogen chloride)
  4. HNO3 (Nitric Acid)
  5. HClO4 (Perchloric Acid)
  6. H2SO4 (Sulfuric Acid)

While there are several other acids to choose from, these are the ones most commonly used in most chemistry courses, including on the AP Chem exam.

12

Please list seven common strong bases.

  1. NaOH (sodium hydroxide)
  2. KOH (potassium hydroxide)
  3. NH2- (amide ion)
  4. H- (hydride ion)
  5. Ca(OH)2 (calcium hydroxide)
  6. Na2O (sodium oxide)
  7. CaO (calcium oxide)

While there are several other bases to choose from, these are the ones most commonly used in most chemistry courses, including on the AP Chem exam.

13
Define and give an example of:

polyprotic acid

A polyprotic acid can donate more than one proton to a solution.

Ex: H2SO4  (can donate 2 protons)

14
Define and give an example of:

an amphoteric substance

An amphoteric substance can act as an acid or a base depending on the solution.

The classic example is water. Acting as a base:

H20 + HA  ⇔  A- + H30+

Acting as an acid:

H20 + B-  ⇔  BH + OH-

15
Define:

conjugate acid-base pairs

Conjugate acid-base pairs are molecules which differ via the presence or absence of a proton. The protonated form of the molecule is the conjugate acid, the deprotonated form is the conjugate base (Brønsted-Lowry acid definition)

Generic equation:

HA + H2O → A- + H3O+

HA is an acid and A- is its conjugate base. Similarly, H2O is acting as a base, with H3O+ acting as its conjugate acid.

16

What is the conjugate base of acetic acid, CH3COOH?

The acetate ion, CH3COO-

An acid's conjugate base is the deprotonated remainder of the molecule's acid reaction. The general acid neutralization reaction is

HA + OH- ⇒ A- + H2O

where HA is the acid, and A- is the conjugate base.

17

What is the product of the reaction of a strong acid and a strong base?

Salt and water, according to the general equation

HA + BOH  ⇒   AB + H20

It is possible to add acid and base and NOT create water (Lewis acid/base pairs) but there will always be a salt formed. Additionally, when you use Bronsted-Lowry as the acid/base definition (like the AP Chem exam does), it is safe to assume that water is always formed as well.

18

What is the purpose of a titration experiment?

The purpose of a titration experiment is to discover the concentration of an unknown acid or base, by neutralizing it with a measured quantity of a base or acid solution whose concentration is known.

In titrations, the known solution is the titrant and the unknown solution is the analyte.

19
Define:

the equivalence point

The equivalence point is the point at which every molecule of acid has been neutralized by a molecule of base.

[H+ ions]original = [OH- ions]added

In a titration, this is where all of the unknown (analyte) has been completely neutralized by the known (titrant), giving a neutral pH.

20

If a weak acid is titrated with a strong base, what is the pH at the equivalence point?

Ex: CH3COOH + NaOH ⇒
      NaCH3COO + H2O

More than 7, slightly basic.

The equivalence point is a point at which the amount of equivalents of acid and equivalents of base from the analyte and titrant are equal.

In the example: a weak base (acetate ion, CH3COO-) is being formed, hence the pH at the equivalence point will be above 7.

21
Define and give an example of:

an indicator

(as it relates to titrations)

In a titration, the indicator changes the color of the solution to indicate that the equivalence point pH has been reached.

Ex: Phenolphthalein goes from colorless to fuchsia between pH 8.3-10
Ex: Methyl red goes from red to green to yellow between pH 4.4-5.2-6.2

22

What are the requirements for an indicator?
Name several common ones.

An indicator is a molecule that must change color visibly in a set pH range, usually a range of about 2 pH units. To select an indicator for a specific titration, find one whose pKa is roughly equal to the pH of the titration's equivalence point.

Some common indicators include:

  • Methyl red (pH range 4.4-6.2)
  • Thymol blue (8.0-9.6)
  • Azolitmin (4.5-8.3)

23
Explain and give the pH value for:

The equivalence point in a strong acid/strong base titration

The equivalence point is a point at which the amount of equivalents of acid and equivalents of base from the analyte and titrant are equal. For a strong acid/strong base combination, this happens at a pH of 7. At the equivalence point:

VA * NA = VB * NB

Where 

  • VA = volume of acid in L
  • NA = normality of acid in #equivalents*mol/L
  • VB = volume of base in L
  • NB = normality of base in #equivalents*mol/L

24
Define and give the common use for:

an analyte

An analyte is an acid or base whose concentration is determined by a titration.

A titrant (known concentration) is used to bring the unknown (analyte) solution up to a standard pH (usually neutral 7).  In this way, the concentration of the analyte can be calculated.

25
Define and give an example of the use for:

titrant

A titrant is a strong acid or base with a known concentration.

In a titration experiment the titrant is used to neutralize, or bring to a known pH, an unknown (analyte) solution.  In this way, the concentration of the unknown can be calculated.

26

In the below titration of the acid H2A, at which point does
[H2A] = [HA-]?

Point A

Point A is the first half-equivalence point, where one-half as many equivalents of base have been added as acid molecules that were in the solution to begin with, so one half of the acid molecules have been neutralized, and [H2A] = [HA-].

27

In the below titration of the acid H2A, what is the earliest point where the solution is entirely A2-?

Point D

A2- production is not complete until 2 full equivalents of base have been added.  This must be at the second equivalence point, which is Point D.

28

What is the chemical process happening to the Ag atom in this reaction?

Ag(s) ⇒ Ag+(aq) + e-

The Ag atom is undergoing oxidation.

The mnemonic to use in redox (reduction-oxidation) reactions is OIL RIG: Oxidation Is Loss (of electrons), Reduction Is Gain (of electrons).

In this case, the Ag atom is losing an electron, so it is being oxidized.

29

What is the chemical process happening to the Fe3+ ion in this reaction?

Fe3+(aq) + e- ⇒ Fe2+(aq)

The Fe3+ ion is undergoing reduction.

The mnemonic to use in redox (reduction-oxidation) reactions is OIL RIG: Oxidation Is Loss (of electrons), Reduction Is Gain (of electrons).

In this case, the Fe3+ ion is gaining an electron, so it is being reduced.

30
Define:

an electrochemical cell

An electrochemical cell is a set of chemical systems which either: 

  1. undergo a reaction and generate electric current, or
  2. undergo a reaction when electric current is run through the system.