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gives the number of atoms of each element in one molecule of the compound
Molecular formulas can be determined by a two-step process. The first step is __.
determination of the empirical formula, the relative ratios of the elements present
How to determine empirical formula.
- 1) Out of 100 grams, convert the percentages to the numbers
- 2) Divide the amount by their atomic mass to convert to moles (g/moles)
- 3) Divide by the smallest number of moles obtained
Molecular weights can be determined by methods that relate the __ or __ of a solvent to the __ of the unknown.
- freezing point depression
- boiling point evelation
- molal concentration
If the compound is volatile, what can we do.
convert it to a gas and use its volume to determine the number of moles according to the gas law
Arrhenius definition of acids and bases
acids: substances that dissociate in water to give hydronium ions
bases: substances that dissociate in water to give hydroxide ions
Arrhenius equations correspond to what scale?
Bronsted-Lowry acid and base definition
acid: any species that donates a proton
base: any species that accepts a proton
One of the most important principles of the Bronsted-Lowry definition is this concept of __
- conjugate acids and bases
- NH3 is a base; its conjugate acid is NH4+
What is Ka and its value?
The stronger the acid...
- acid-dissociation constant
- value indicates the relative strength of the acid
- the more it dissociates, the larger value of Ka
For an acid to be strong, its conjugate base must be __. Therefore, it must be a __
- stable in its anionic form
- weak base
In the reaction with an acid and base, the equilibrium generally favors the __
weaker acid and base
Equilibrium constant for the reaction of a base is called the __.
base dissociation constant (Kb)
Multiplying Ka and Kb should give you the __
water ion-product constant (1 x 10^-14)
True or False:
Acid base reactions favor the stronger acid and the stronger base
- True or False:
- Acid base reactions favor the stronger acid and the stronger base
To be a Bronsted-Lowry acid, a compound must contain __.
A strong acid must have __.
- a hydrogen atom that can be lost as a proton.
- a stable conjugate base after losing the proton
The stability of the conjugate base is a good guide to __.
More stable anions tend to be __, and their conjugate acids are __/
Some of the factors that affect the stability of conjugate bases are __, __, and __.
- resonance stabilization
A more electronegative element bears what more easily, giving a more stable conjugate base and a stronger acid
a negative charge
The negative charge o an anion is more stable when?
if it is spread over a larger region of space
What is the periodic trend for acidity?
increases down the column, as the size of the element increases
The negative charge of a conjugate base may be __ over two or more atoms by __. Depending on how electronegative those atoms are, and how many share the charge, __ is often the dominant effect helping to stabilize an anion.
- resonance delocalization
Acids are stronger if they __.
lose a proton to give resonance-stabilized conjugate bases
__ can also stabilize a conjugatebase through the __ of the molecule. Stabilization of the conjugate base results ina __ acid (__ value of pKa).
- electron-withdrawing atoms and groups
- sigma bonds
The magnitude of this __ depends on the nmber of bonds between __.
- inducive effect
- electronegative element and the site of the negative charge
Stronger electron withdrawing groups stabilize the __ of the conjugate base more than weaker groups, leading to __.
Multiple electron-withdrawing grojups do what?
increase the acidity more than a single group
Lewis acid and base definitions
- base: species with available electrons that can be donated to form new bonds
- acid: species that can accept these electron pairs to form new bonds
Since a Lewis acid accepts a pair of electrons, it is called an __. A Lewis base is called a __ because it donates electrons to a nucleus with an empty or easily vacated orbital.
True or False:
Lewis acids and bases have nothing to do with protons.
How do we distinguish Bronsted-Lowry acids and bases from Lewis acids and bases?
Bronsted Lowry are simply referred to as acids and bases. Lewis acids are electrophiles and lewis bases are nucleophiles
__ is used to show the flow of an electron pair __.
- curved-arrow formalism
- from the electron donor to the electron acceptor
Electrons do not "flow" in resonance structures; they are __.
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