Chemistry Exam 2

Unit mole

The amount of a substance containing the same number of discrete entities (atoms, molecules, ions) as the number of atoms in a sample of pure carbon-12 weighing exactly 12g

1 mol contains 6.022 × 10²³, Avogadro’’s Number

Concentration

Relative amount of a given solution component

Solvent

Component with the highest concentration (water) 

Solute(s)

Dissolved component(s) present at a much lower concentraiton. Solute can be dilute (low concentration) or concentrated (high concentration). 

Molarity (M)

The number of moles of solute(n) in exactly 1 L of solution

M = mol solute/L solution = n/V (in L)

Mass percentage

The ratio of solute to solution mass expressed as a percentage

Mass of component/mass of solution x 100

Volume percentage

The ratio solute to solution volume expressed as a percentage

Volume of solute/volume of solution x 100

Mass volume percentage

The ratio of solute’s mass to solution volume expressed as a percentage

Mass of solute/volume of solution x 100Pa

Parts per million

PPM = mass of solute/mass of solution x 10^6

1 PPM = 1 mg/kg

Parts per billion

PPB = mass of solute/mass of solution x 10^9

1ppb = 1mg/kg

Precipitation reactions

Occur when dissolved ions form insoluble combination

Solution becomes cloudy and solid collects on bottom

The solubility has been exceeded 

Soluble compounds contain:

-Group 1 metal cations

-Ammonium ion (NH4+)

-The halide ions (F-, CI-, Br-, I-)

-The acetate (C2H3O2-), bicarbonate (HCO3-), nitrate (NO3-), chlorate (CIO3-) ions, sulfate ion (SO4 2-)

Insoluble exceptions:

The halides of Ag+, Hg2 2+, Pb 2+

Sulfates of Ag+, Ba 2+, Ca 2+, Hg2 2+, Pb 2+, Sr 2+

Insoluble compounds contain:

-Carbonate (CO3 2-)

-Chromate (CrO4 2-)

-Phosphate (PO4 3-)

-Sulfide ions (S2-)

-Hydroxide ion (OH-)

Soluble exceptions:

-Compounds of these ions with group 1 metal cations

-Ammonium ion (NH4+)

-Hydroxides of group 1 metal cations and Ba 2+

What are the group 1 metal cations?

Li+, Na+, K+, Rb+, Cs+

Cyanide

CN-

Hydrogen phosphate

HPO4 2-

Dihydrogen phosphate

H2PO4-P

Perchlorate

CIO4-

Chlorate

CIO3-

Chlorite

CIO2-

Hypochlorite

CIO-

Thiosulfate

S2O3 2-

Oxalate

C2O4 2-

Cyanate

OCN-

Thiocyanate

SCN-

Chromate

CrO4 2-

Dichromate

Cr2O7 2- 

Acid-base reactions

Occurs when hydrogen ion (H+) is transferred from one chemical species to another

What is an acid?

A substance that dissolves in water to release H3O+ ions

What is a strong acid?

An acid that ionizes completely to form H3O+ ions

What is a weak acid?

A weak acid partially reacts 1% with water

What is a base?

A base is a substance that dissolves in water to yield OH-

What is a strong base?

A strong base disassociates into cations and OH- ions completely in water

What is a weak base?

It only reacts partially with water

What are the strong acids?

HBr - hydrobromic acid

HCI - hydrochloric acid

HI - hydroiodic acid

HNO3 - nitric acid

HCIO4 - perchloric acid

H2SO4 - sulfuric acid

What are the strong bases?

LiOH

NaOH

KOH

Ca(OH)2

Sr(OH)2

Ba(OH)2

What is the oxidation number of an atom in an elemental substance?

Zero

What is the oxidation number of a monatomic ion?

It is equal to the ion’s charge

What is hydrogen’s oxidation numbers?

+1 with nonmetals, -1 combined with metalsO

What oxidation number does oxygen have?

-2 in most compounds, sometimes -1 in peroxides

What is the oixation number for halogens?

—1 for F always

-1 for other halogens except when combined with oxygen or other halogens (positive oxidation numbers with varying values) 

What does the sum of the oxidation numbers for all atoms in a molecule or polyatomic ion equal?

It equals the charge on the molecule or ion

Redox reactions

Electrons are transferred

Some redox reactions involve the transfer of electrons between reactants to make ionic products

Limiting reactant

To find, compare the amount of product expected for each reactant 

It involves comparing the amount of product expected for the complete reaction of each reactant. The reactant yielding the lesser amount of product is the limiting reactant

Theoretical yield

The amount of product that may be produced by a reaction as calculated per stoichiometry using limiting reactant of an appropriate balanced chemical equation

Titrations invovle:

2 solutions: titrant and analyte

Titrant

a solution containing a known concentration of one reactant

Analyte

solution containing a reactant of unknown amount or concentration

Indicators

Added to analyte solution to impact a change in color at or very near the equivalence point of the titration

End point

Volume of titrant actually measured

What is a buret?

A buret is a graduated glass cylinder with a valve at the bottom that has volume readings from 0 to 50 mL. The volume of titrant added has reached the end point can be easily measured to the enarest 0.01 mL by the change in volume readings

What is gravimetric analysis?

It is an analysis in which a sample is subjected to some treatment that causes a change in the physical state of the analyte that permits its separation from the simple compound

Dilution

process whereby solution concentrated is lessened by solvent addition