Chapter 16: Equilibrium in Acid-Base Systems: Flashcards
What is an ideal buffer?
One in which the concentration of an acid and its conjugate base are the same.
What happens when one of the 5 strong acids (since H2SO4 excluded) react with a strong base?
A quantitative reaction with an endpoint at ph=7
What entities cannot be part of a buffer region?
H30+ and OH- (which is why many SA/SB rxns have only one buffer region)
What is Kw?
The equilibrium constant in the water ionization equilibrium; Kw={H30+}{OH-}=1x10-14 at SATP
How else can you study?
Go through all examples in textbooks (worked and hmwk)
Why do strong acid reactions have 1 right arrow instead of 1 L/R?
Because strong acids react quantitatively with water to form hydronium ions
What separates wa/wb and SA/SB?
Not only do SA/SBs react quantitatively with water, they are stronger electrolytes and react faster.
What is implied if entities not found on table are found at last equivalence point?
Since these entities can’t affect ph, it must imply any entities that could have been completely consumed, indicating a SA/SB rxn.
What is a Bronsted Lowry acid?
A proton donor
What is a bronsted lowry base?
A proton acceptor
What is a bronsted-lowry rxn equation?
A chemical rxn equation showing an acid-base rxn involving transfer of proton from one entity (acid) to another (base)
What is an amphoteric species?
A chemical substance with the ability to react as an acid or base.
What is an amphiprotic species?
An entity with the ability to either accept or donate a proton.
Which type of compound will always be amphiprotic?
All hydrogen polyatomics are amphoteric since they can both donate a hydrogen ion and accept one.
What is a conjugate acid-base pair?
A pair of substances with chemical formulas that differ only by a proton. They appear opposite each other on table.
What should you do when finding sa/sb?
Check table for amphiprotic species.
Generalization regarding relative strengths of acid-base conjugate pairs?
The stronger an acid, the weaker its conjugate base. Conversely, the weaker an acid, the stronger its conjugate base.
Explain strengths of acids and bases in terms of attraction to hydrogen proton:
The stronger an acid, the weaker its attraction to its proton (wants to give it up), and the stronger a base, the stronger its attraction for protons (wants to receive).
What is the strongest acid entity that can exist in a reaction?
H3O+. If a stronger acid (6) than hydronium ion is dissolved in water, it reacts instantly and quantitatively to form hydronium ions. 6 SA’s written as H3O+ when in aqueous solution.
What is the strongest base entity that can exist in aqueous solution?
OH- is strongest base entity that can exist in aqueous solution. If a stronger base entity than hydroxide ion is dissolved in water, it reacts instantly and quantitatively to form hydroxide ion. (ex: Soluble ionic oxide compounds like Na2O (s) are Na+ and OH- in solution).
Why are the conjugate bases of the 6 SAs not considered bases in aqueous solutions?
Because no entity in aqueous solution can react as a base if it is a weaker base than water (H20(l) always present).
What is Ka?
The equilibrium constant for the ionization of weak acids. Also known as dissociation constant.
What is ionization?
Process by which electrically neutral entities are converted to charged atoms or molecules (ions).
What is hydrolysis?
Changing the chemical composition of an entity due to reaction with water.
What is Kb?
The equilibrium constant for the ionization of weak bases. Also known as base dissociation constant.
What is a ph curve?
A graph showing the change in ph as the volume of titrant increases.
What is a buffer?
A mixture of a conjugate acid-base pair that maintains a nearly constant ph when diluted or when a SA/SB is added to it.
What is a buffer?
A mixture of a conjugate acid and its base pair that maintains a nearly constant ph when diluted or when a SA/SB is added to it.
Ph of wa/SB rxn:
Equivalence point above 7.
Ph of SA/SB (see sulfate?) rxn:
SA/SBs react quantitatively to form h2o and have an equivalence point at 7.
Ph of SA/SB (see sulfate?) rxn:
SA/SBs react quantitatively to form h2o and have an equivalence point at 7.
What is buffer capacity?
The limit of the ability of a buffer to maintain a nearly constant ph.
What is another name for acetic acid?
Vinegar, or ethanoic acid.
Is a scientific concept ever complete?
No, this mindset limits further progress in the respective field as this is not usually the case.
Why do bronsted-lowry acid-base rxns always have 1:1 ratio?
Because they display a transfer of 1 proton between the entities involved.
What is another word for inflection point?
Midpoint
What are indicators, and how are they formed?
Indicators are weak acid-base pairs that display different colors in their acid, or base form (depending on ph). They are formed when an indicator dye dissolves in water.
What type of molecules are indicators?
They are usually complex molecules, because simpler molecules wouldn’t interact with visible light waves?
Why is a single arrow used in a titration run?
Because reaction in titrations must be quantitative for any stoichiometric equations to be valid (other rxns?).
What should you do after finishing a question?
Say “I am saying that …(question) implies …” and then ask yourself “Is this logical?” after going over your thought process
What should you do after finishing a test?
Look it over until the time runs out.
What are you suppose to do when a weak polyproctic acid or base is initially dissolved in water?
You assume that the ionization equilibrium only involves the first proton transfer-to or from water. This is because the likelihood of an entity formed by a first ionization to lose or gain a second proton is much less than the original entity dissolved (so much so that it can be considered negligible).
What is the endpoint of a titration?
Actual point in titration where a sudden change is observed (ph or indicator color), thus indicating that the equivalence point has been reached (titrant has completely reacted with sample)
What is the equivalence point of a titration?
The theoretical volume of titrant that should be added to react completely with sample.
What are polyprotic acids?
Acids that can lose more than one proton (at least h2).
What are polyprotic bases?
Bases that can gain more than proton(usually at least -2).
What does an equivalence point represent in a ph curve?
Each equivalence point represents a proton transfer in a quantitative reaction.
How are buffers prepared?
By mixing a weak acid with a salt solution of that weak acid.
What is the function of H2PO4- and HPO4(2-) in the body?
Buffers H2PO4- and conjugate base HPO4(2-) maintain a stabilized ph in the internal fluid of living cells (in cytoplasm).
What is the function of H2CO3 and HCO3- in the body?
Buffers H2CO3 and its conjugate base HCO3- are mainly responsible for maintaining ph in blood, and most bodily fluids (besides cell cytoplasm).
What are some uses of buffers in industry?
To avoid side reactions in drug production, maintain ph of dairy products being made, and preserve food.
What are sig dig tips for acid-base questions?
For ph, all numbers that would normally be sig digs, but ONLY starting after decimal are sig digs. If Ka/Kb values were used in the calculation process use them as sig digs (2).
What should you watch out for when given chemical equations?
THAT THE EQUATION YOU’VE BEEN GIVEN IS BALANCED.
What is another way of explaining what determines the position of an acid-base equilibrium?
The competition for proton transfer of the reacting species in the forward direction, and the reacting species in the reverse direction.
How to know if an acid/base reaction favours the products?
If the proton donor (acid) is higher than the proton acceptor (base) on the table of acid-base strengths, then the products will be favoured.
What to remember when finding the ph/poh of a BASE?
Use Kb value in calculations (table gives you Ka values), and remember kb=kw/ka. Also in any Kc calculation you can ignore change in concentration if initial concentration is 1000 times greater than Ka/Kb.
What is small, yet distinct difference between strong acid and weak acid ph curves?
Strong acids go straight from the start, weak acids have small inflection before buffer region.
