Chemistry Midterm

Observations

recording of natural phenomena

Qualitative

descriptive elements, ex: color, texture, smell

Quantitative

measurements, ex: length or mass

Inference

a conclusion based on logic

Hypothesis

  a possible explanation for the observations that needs to be tested

Theory

 a unifying principle that explains experimental results; predicts new outcomes

Law

 a universal statement or equation describing consistent natural phenomena based on repeated observations and experiments.

Sig Figs

• - the total number of digits in a number

  • Zeros in the middle of a number are like any other digit; they are always significant. 

  • Zeros at the beginning of a number are not significant; they act only to locate the decimal point. 

  • Zeros at the end of a number and after the decimal point are always significant.

  •  Zeros at the end of a number and before the decimal point may or may not be significant.

Sig figs in calculations

• In carrying out a multiplication or division, the answer can’t have more significant figures than either of the original numbers.

• In carrying out an addition or subtraction, the answer can’t have more digits to the right of the decimal point than either of the original numbers.

Rounding Sig figs

• If the first digit you remove is less than 5, round down by dropping it and all following digits.

• If the first digit you remove is 5 or greater, round up by adding 1 to the digit on the left.

Accuracy

 how close to the true value a given measurement is

Precision

how well a number of independent measurements agree with one another

Fundemental SI Units

Physical quantity	Name of unit	Abbreviation
Mass	kilogram	kg
Length	meter	m
Temperature	kelvin	K
Amount of substance	mole	mol
Time	second	s
Electric current	ampere	A
Luminous intensity	candela	cd

Derived Quantities

Area	Length x length	m2
Volume	Area x length	m3
Density	M/V	kg/m3
Speed	Distance/Time	m/s
Acceleration	Change in speed per unit time	m/s2
Force	Mass x acceleration	N, newton
Pressure	Force per unit area	Pa, Pascal
Energy	Force x distance	J, joule

Numerical prefixes

Factor	Prefix	Symbol	Example
1012	tera	T	1 teragram (Tg)
109	giga	G	1 gigameter (Gm)
106	mega	M	1 megameter (Mm)
103	kilo	k	1 kilogram (kg)
102	hecto	h	1 hectogram (hg)
101	deka	da	1 dekagram (dag)
10-1	deci	d	1 decimeter (dm)
10-2	centi	c	1 centimeter (cm)
10-3	milli	m	1 milligram (mg)
10-6	micro	μ	1 micrometer (μm)
10-9	nano	n	1 nanosecond (ns)
10-12	pico	p	1 picosecond (ps)

Water Temperature

Farenheit, water boils @ 212 and freezes @ 32

Celsius, Water boils @ 100, and freezes @ 0

Kelvin, Water boils @ 373, and freezes @ 273

Reading Graduated cylinder

• Read bottom of meniscus

• If inbetween lines estimate

A metals

Alkali Metals and Alkaline Earth Metals

Halogens

Group 7a

Noble Gases

Group 8a

Groups

vertical columns on the periodic table

Periods

horizontal columns on the periodic table

Metals

• All except mercury are solid

• Most have silvery shine

• Malleable rather than brittle

• Good conductors of heat and electricty

Semimetals

• Silvery

• Solid

• Brittle

• Bad conductor

Nonmetals

• Not silvery in appearance 

• Several are brightly colored, 

• Brittle

• Bad conductors of heat and electricity

Physical Properties

• characteristics that do not involve a change in chemical make up

  • Can be reversed

  • Ex. Change in state

Chemical Properties

•  characteristics that do involve a change in chemical makeup

  • Ususally cannot be reversed

  • Ex. Rust

Law of Conservation of Mass

Mass is neither created nor destroyed in chemical reactions

Law of Definite Proportions

Different sample of pure chemical substance always constrain the same proportions of elements by mass

Law of Multiple Proportions

When two elements combine in different ways to form different substances, the mass ratios are small, whole-number multiples of on another

Daltons 4 theories of the atom

• Elemetns are made up of tiny parircles called atoms

• Each element is characterized by the mass of its atoms, atoms of the same elements hace the same mass, but atoms of different elements have different masses

• The chemical combination of elements to make different chemical compounds occurs when whole numbers of atoms join in fixed proportions.

• Chemical reactions only rearrange how atoms are combined in chemical compounds; the atoms themselves don’t change.

Cathode Ray Tube Experiment

• Thomson passed an electric current through a cathode ray tube, producing a beam of particles (later identified as electrons).

• He observed that the beam was deflected by electric and magnetic fields, indicating the particles were negatively charged.

Key Discoveries:

1. Atoms contain tiny, negatively charged particles called electrons.

2. These electrons are much smaller than atoms, meaning atoms are divisible.

Plum Pudding Model

• Proposed that an atom consists of a uniform, positively charged "pudding" with negatively charged electrons embedded within it, like "plums" in a pudding.

• This model suggested no centralized nucleus and assumed a diffuse positive charge.

Subatomic Particles

Electrons	Ouside the nucleus, Negative charge
Protons	Inside the nucleus, positive charge
Neutrons	Inside the nucleus, no charge

Isotope

 Atoms with identical atomic numbers but different mass numbers

Isotope notation

Mass Number/Atomic number X

Atomic Numbers

 the number of protons in an atoms nuclues, displayed on periodic table

Mass Number

• The sum of protons and neutrons

  • Mass number(A) = Number of Protons(Z) + Number of Neutrons(N)

  • In a neutral atom the number of protons and electrons are equal

How to name monoatomic anions (e.g. oxide, sulfide, etc.)

If it is a single element with a negative charge it has the suffix -ide

AC Ionic compound

Contain an A-metal and a non-metal

BC Ionic compound

Contains a B-metal and a non-metal

Polyatomic ionic compounds

Any compound containing 1 or more polyatomic ions

Ionic compound naming

• Name of Cation + Name of Anion, will always have a neutral charge, no numerical prefix, only possible number is Roman Numeral

Criss-Cross method

• 1. Find individual ions

• 2. Criss-Cross, turn superscripts into opposite subscripts

• 3. Simplify the ratio

Oxyacids

Compounds that contain hydrogen, oxygen, and another element

Moles

• A mole is a unit of measurement which is equal to avagradros number

  • Avagadro’s number  - 6.0221023

  • Molar mass -  the mass of 1 mol of substance; equal to the molecular or formula mass of a substance in grams

Mixture

 a blend of two or more substances in some arbitrary proportions

Homogenous

 A mixture with a uniform composition throughout, where components are indistinguishable.

Heterogenous

A mixture with a non-uniform composition, where distinct components are visible.

Pure Substance

 A material with the same composition and distinct chemical properties, either an element or a compound.

Element

A pure substance consisting of only one type of atom, defined by its atomic number

Chemical Compounds

 A pure substance formed when two or more elements chemically bond in fixed proportions.

Chemical Bonds

the force that holds atoms together in chemical compounds

Covalent Bonds

A bond that occurs when two atoms share several electrons

Ionic Bonds

a bond results from a transfer of one or more electrons between atoms

Ion

A charged atom or group of atoms

Cation

a positively charged atom or group of atoms

Anion

 a negatively charged atom

Molecule

The unit of matter that results when two or more atoms are joined by covalent bonds

AC Ionic Compounds

• two elements, one metal and one nonmetal

• Metal Name: The metal keeps its original name.

• Nonmetal Name: The nonmetal's name is modified to end in "-ide."

BC Ionic Compounds

• Some transition metals can have multiple charges (oxidation states). You specify the charge of the metal using Roman numerals in parentheses.

• Naming: Name the metal first, followed by the nonmetal with "-ide."

Ionic Polyatomic Compounds

Polyatomic ions are groups of atoms that act as a single ion. If a compound contains a polyatomic ion, you keep the name of the polyatomic ion.

Oxoanions

an anion of an oxoacid

Binary Molecular Compounds

• only two covalently bonded nonmetals

  • Prefix System: Use prefixes to indicate the number of atoms of each element in the compound. The prefixes are: mono-, di-, tri-, tetra-, penta-, hexa-, hepta-, octa-, nona-, deca-.

• The first element keeps its name, while the second element's name ends in "-ide."

Note: The prefix "mono-" is usually omitted for the first element.

Naming Acids

• Binary Acids (hydrogen + nonmetal):

• Start with "hydro-" followed by the name of the nonmetal with the suffix "-ic," then add "acid."

Oxyacids

 (contain hydrogen, oxygen, and a polyatomic ion):

• If the polyatomic ion ends in "-ate," change the suffix to "-ic."

• If the polyatomic ion ends in "-ite," change the suffix to "-ous."

Aqueous

dissolved in water

Stoichiometry

• the mole:mass relationships between reactants and products

Limiting reactant

The reactant in a chemical equation that limits the amount of product produced

Excess reactants

The reactant in a chemical equation that does not limit the amount of product produced and therefore contains more reactant than needed and is in excess

How to find the limiting reactant

• If the given reactants are in mass, usually grams, you must convert them to mols using the conversion factor 1 mol x/molar mass of x

• Then you multiply by the mol ratio of product/given

• Last, you multiply by the conversion factor of molar mass of product/1 mol of product

• The reactant which gives you the least amount of product is the limiting reactant and all other reactants are in excess

How to find the remaining amount of excess

• Find the limiting and excess reactant

• Convert the limiting reactant into mols if not already

• Multiply by the mol ratio of excess reactant/limiting reactant

• Multiply the mols of excess reactant by the conversion factor of molars mass of excess reactant/1 mol excess reactant

• Lastly, put it into the formular Initial Mass - Final Mass = remaining mass

Percent Compostion and Empirical Formulas

• Percent Composition - How much each component contributes to a compound

  • Formula - %Comp = Mass component/Mass of compound x 100

  • The sum of all components should add to 100%

Empirical Formula

The formula which displays the lowest mol ratio of atoms in the compound

How to find the empirical formula

• Convert % to grams by assuming 100g sample

• Convert given mass to mols using 1 mol xmolar mass x

• Write an initial formula using the form X_0.00Y_0.00, Where the variables are the atoms and the numbers are the mols of each atom

• Then divide the whole formula by the smallest coefficient

• Multiply the equation by whole number integers until the other coefficient is within 0.05 of a whole number

• *NOTE: Do NOT round any of the numbers before the last step to ensure accuracy

Molecular Formula

the formula which displays the actual numbers of atoms in a compound

Multiple

• molecular weight/emprical formula

  • Molecular weight must be given

  • If the multiple is within 0.1 of a whole number you can round it

  • If it is not, then find a fraction that is equivalent or close to the number and multiply it by the number which would make the fraction a whole number

Molarity

•  the number of moles divided by the liters of solution

  • Use C= n/v

    • C = concentration

    • N = number of moles

    • V = volume

Dilution

•  adding solvent to concentrated solution to reduce concentration

  • C1V1 = C2V2

  • Take givens and manipulate the formula

Electrical current 

•  the flow of charged particles

  • Electrons flow along Cu wire

  • Ions flow through aqueous solutions

electrolytes

substances that dissolve in water to produce conducting solutions of ions

non-electrolyte

substances that do not produce ions in aqueous solutions

• Molecular compounds are generally non-electrolytes

Dissociation

•  when ionic compounds dissolve in water they split spart into ions

  • Solid NaCl is not conductive because their is no medium for the ions to flow

Strong electrolytes

• compounds that dissociate to a large extent(70%-100%) into ions when dissolved in water

  • Strong electrolyte because it completely dissociates

  • Uses arrow because it cannot go back into solid

Weak electrolytes

• compounds that dissociate to a small extent into ions when dissolved in water

  • Not 100% dissociated, most remains neutral molecules 

  • Less conductive

  • uses double arrow

Acid-Base neutralization

•  processes in which an acid reacts with a base to yield water and a salt

• Double replacement reaction

• Always has water and a salt as product

Acid

• a substance that dissociates in water to produce hydrogen ions, H⁺

H⁺

• H⁺ is just a proton

  • Not very stable

    • Latches onto a water molecule

    • Becomes H₃O⁺ 

Hydronium

In water, acids produce hydronium ions, H₃O⁺

• H⁺ and H₃O⁺ are interchangeable 

• H⁺ is unrealistic and H₃O⁺ is more accurate

Base

• a substance that dissociates in water to produce hydroxide ions OH^-

  • Ammonia is a weak base because it reacts to a small extent w/water to yield ammonium and hydroxide ions

    • Weak base = doesn’t full dissociate

      • Conductivity test

To find whether a reaction is basic, acidic, or neutral

• find mass of both acid and base and subtract them the one with more will be the answer

  • Neutral means the subtraction was 0