Chem 1A Midterm 3- Acids and Bases

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T/F: Whether you start with all reactants or products (or a mix of both), the composition of the final equilibrium mix is always the same

True

What does K represent?

Equilibrium constant - numerical value defining the ratio of product concentrations to reactant concentrations for a reversible reaction at equilibrium

What is a reversible reaction?

Process where reactants form products that can also turn back into reactants. This helps reach equilibrium. Symbolized by double arrow

When a given equation is aA + bB ⇌ cC + dD, what will the equilibrium equation look like?

[C]^c [D]^d / [A]^a [B]^b

What is the equation for K?

products/reactants

What forms of matter are NOT used to calculate equilibrium?

Solid and liquid - you ONLY use aqueous and gas

What do brackets [ ] represent?

Units of molarity

What is the equation for molarity (M)?

mol/L

What does the K equation look like when using partial pressures?

P_C^c P_D^d / P_A^a P_B^b

When do you use the partial pressure K equation?

ONLY with gases

When is a reversible equation reactant favored? (What size of K?)

When the denominator is bigger

or

K < 1

When is a reversible equation product favored? (What size of K?)

When the numerator is bigger

or

K > 1

What is a forward reaction rate in a reversible reaction?

Signals how “easy” the forward reaction is (reactants → products)

What is the equation for forward reaction rate?

K_f [X]

Where K_f = rate constant and [X] depends on the quantity of the reactant

What is a backward reaction rate in a reversible reaction? What does it depend on?

Signals how “easy” the backward reaction is (products → reactants)

Depends on how many products you have

What is the equation for backward reaction rate?

K_b [Y]

Where K_b = rate constant and [Y] depends on the quantity of the product

What is chemical equilibrium?

A state all reversible reactions reach where amounts are no longer changing because the forward and backward reates are equal

What is the reaction quotient (Q)?

Amounts of reactant and product in equation at any time (not at equilibrium)

How are K and Q different? How are they the same?

Same equation, but it is only K if the concentrations are at equilibrium (if it’s not equilibrium, it’s just Q)

What does a system under “stress” refer to?

System at a non-equilibrium condition

Le Chatelier’s Principle

An equilibrium system subjected to stress will move in the direction that relieves stress and returns system to equilibrium

According to Le Chatelier’s principle, if a system is Q > K, in which direction will the system shift?

There are too many products, so shift to reactants

According to Le Chatelier’s principle, if a system is Q < K, in which direction will the system shift?

There are too many reactants, so shift to products

If there are more collisions, what happens to the reaction speed?

Reaction becomes faster and opposite reaction speeds up to match

What kind of impact will a temperature change have on a system?

Stresses a system to change the K

If ΔH > 0, will heat be a product or reactant?

Reactant

If ΔH < 0, will heat be a product or reactant?

Product

What does a large K_b represent?

Easy backward reaction

What does a large K_f represent?

Easy forward reaction

What does K_c > 1 represent?

Mostly products @ equilibrium

What does K_p < 1 represent?

Mostly reactants @ equilibrium

What does Q > K represent?

Shift to reactants, too many products

What does Q < K represent?

Shift to products, too many reactants

If K > > 1, does that signify more dissolved products or more undissolved reactants?

More dissolved products

• Will turn back into reactants to reach equilibrium (form a precipitate)

If K < < 1, does that signify more dissolved products or more undissolved reactants?

More undissolved reactants

• Will create more products to reach equilibrium

What kind of solubility does a big k value signal?

Very soluble

What kind of solubility does a small k value signal?

Not very soluble

What does K_S represent?

Whe a liquid dissolves in H2O

What does K_H represent?

When a gas dissolves in H2O

What does K_SP represent?

When a solid dissolves in H2O

Regardless of subscript, what do all K have in common?

PRODUCTS / REACTANTS !!!!!! !!!!

If a solution has more than the maximum amount of reactant, it’s a type of stress. What happens to the solution in this situation?

The solution is at its maximum saturation, so it forms a precipitate

How does K relate to solubility?

K is the maximum solubility

What will happen to a solution if there are molarities above K? What about below K?

If molarities above K, precipitate will form

If molarities below K, that’s okay — the solution just won’t be at max saturation

With an ionic solid solubilizing, what will the chemical equation look like?

Splits into either element

ex) PbCl₂(s) ⇌ Pb²⁺ (aq) + 2Cl^- (aq)

What is a RICE table?

Reaction, initial, change, equilibrium

What stages of matter are left out of a RICE table?

Solid and liquid

What is the common ion effect?

The presence/addition of common ions reduces solubility

When diluting, how do you account for total volume and M change?

M decreases and L water increases

Remember to add L of both reactants together!

What is dissociation?

Dissolution of charged ions in water

What is an acid?

Releases H+ in water (aka a proton or hydronium)

What is the generic form of an acid equation?

HA (aq) + H₂O (l) ⇌ A^- (aq) + H₃O⁺ (aq)

What is partial ionization?

Some acids dissociate completely and make a lot of product, but others only dissolve a bit → this is partial ionization

Strong acids are (good/bad) at being acids

Good!

What is a characteristic of a strong acid?

Loses ALL protons to form lots of H₃O⁺

What are the strong acids we need to memorize?

HBr, HCl, HI

Strong acids have a (large/small) K_a

Large

Weak acids are (good/bad) at being acids

Bad

What is characteristic of weak acids?

Lose some of their protons to make SOME H₃O⁺

How can you identify a weak acid?

COOH group

Weak acids have a (large/small) K_a

Small!

What is a base?

Releases OH^- in water

How can a base make OH?

1) Forming it from reactants

2) “Finding” it from the background H2O

What is the general form of a base equation?

B (aq) + H₂O (l) ⇌ BH⁺ (aq) + OH^- (aq)

Strong bases are (good/bad) at being bases

Good!

What is characteristic of a strong base?

Completely dissolves to create lots of OH^-

How can you identify a strong base?

Metal + OH^-

Strong bases have a (large/small) K_b

Large

Weak bases are (good/bad) at being bases

Bad

How do weak bases often form?

Stealing protons from water to make SOME OH^-

How can you identify a weak base?

N with lone pair

Weak bases have a (large/small) K_b

Small

How can you tell if something is neutral?

If an OH^- is not attached to metal or CO then it may be neutral

What does “p” mean?

-log( )

What is pH?

-log(H+)

What is pOH?

-log(OH-)

What does a low pH indicate? A high one?

Low - acid

High - base

What is x in -log(x) when finding pH?

mol/L aka M

What is “act one”? When do you use it?

Writing balanced equation → finding excess reactant

When you only have strong substances

What is “act two”? When do you use it?

RICE table, when you have only weak substances

What is neutralization?

When there are equal moles of strong acid and strong base

When combining unequal moles of strong acid and base, what determines pH?

Excess reactant

What is the equation for moles?

M x vol

How can you find pH from pOH?

pH = 14 - pOH

How are pH and pOH related?

Inversely

What is a conjugate base?

Product formed when acid loses proton

Acts as a base in reverse reaction

When should you “worry about” a conjugate base?

When acid is weak

What is a conjugate acid?

Product formed when base gains proton

When should you “worry about” a conjugate acid?

When base is weak

When do you know if you made pOH?

If the product of a reaction is OH

A strong acid is a (strong/weak) base

Weak

A strong base is a (strong/weak) acid

Weak

What is the equation for K_w?

K_a x K_b = K_w = 1.0 × 10^-14

What is the equation for pK_a and pKb?

pK_a + pK_b = 14

What does x represent when filling out a RICE table?

Reactant lost and product gained

What does each segment of this graph represent?

First segment (lower horizontal stretch) = excess acid

Vertical segment = equal moles of titrant and analyte

Second segment (higher horizontal stretch) = excess base

What is titration?

Gradually adding a known acid or base to a sample to gain info about the system

What is known in a titration?

Volume

What is unknown in a titration?

Concentration or identity

What is titrant?

The thing being added