Chemistry. The Central Science
What's the difference between hypothesis, theory, and law?
Hypothesis --> “an educated guess”; a tentative explanation of phenomena
Theory --> A widely accepted explanation of natural phenomena, has stood up to thorough and continual testing
Law -->a statement of what always occurs under certain conditions
How can you calculate the mass number of an element?
Mass number = protons + neutrons
What is the molecular mass of N2O4?
(2*14.007) + (4*15.999) = 92.01
What is the difference between molecular, complete ionic and net ionic?
molecular --> shows all reactants and products
complete ionic --> shows the reactants and products as individual ions
net ionic --> shows the reactants and products directly involved in the reaction
density = mass/volume
Define what's an element and what's a compound?
FOR DOUBLE POINTS. What's the difference between homogeneous and heterogeneous?
Element – one type of atom
Compound – two or more element
Homogeneous – cannot be separated physically
Heterogeneous – can be separated physically
What is the symbol for Manganese, Silicon, Calcium, and Bromine?
Mn, Si, Ca, Br
Find the molecular mass for Sn in SnO2
molecular mass of O2 = 2*15.999 = 31.998
molecular mass of SnO2 = 118.71 + 31.998 = 150.708
percent composition of Sn= (118.71/150.708)*100 = 78.76821%
Write the net ionic equation for
AgNO3 + Na2SO4 --> Ag2SO4 + 2NaNO3-
What is the formula for calculating average atomic mass?
average atomic mass = the sum of percentage in decimal multiplied by the isotope mass
Physical changes: a change that occurs without modifying the chemical composition of matter, usually reversible, new products are not formed, changes occur with changes in temperature
Chemical changes: a change that modifies the chemical composition of matter, usually irreversible, new products are formed, changes occur with absorption or release of energy
K(+) --> protons=19, electrons=18
Fe(3+) --> protons=26, electrons=23
Cu(2+) --> protons=29, electrons=27
Balance Zn + AgCl --> ZnCl2 + Ag
Zn + 2AgCl --> ZnCl2 + 2Ag
Cs = +1, O= -2
Ca= +2, I= -1
How can you find the molecular mass in amu?
molecular mass= the sum of (amount of element in compound * molar mass of the element)
Why does 4.6*10^19 has only two significant figures?
Tailing zeros before the decimal point do not count as significant figures
How can you determine if a compound is ionic or covalent/molecular?
Covalent compounds --> both elements are nonmetals
Ionic compounds --> one element is metal, the other one is nonmetal
How many atoms are in 5.10 moles of sulfur?
FOR DOUBLE POINTS, WHAT IS AVOGADRO'S NUMBER WITH UNITS?
number of atoms = moles * Avogadro's number
Avogadro's number = 6.022*10^23atoms/mol
numer of atoms = 5.10 * (6.022*10^23) = 3.07122*10^24
Give the structure for all combination, decomposition, single displacement, and double displacement
(Combination) A + B --> AB
(Decomposition) AB --> A + B
(Single Displacement) AB + C --> AC + B
(Double Displacement) AB + CD --> AC + BD
How can you calculate percent composition?
percent composition = (molecular mass of element/molecular mass of compound) * 100
What's the difference between precision and accuracy?
Precision: refers to how close the measurements are to each other, indicating consistency
Accuracy: refers to how close the measurements are to the true or accepted value
Write the empirical formula for N4Cl12, I3F21, Xe2O8
FOR DOUBLE POINTS, NAME THE COMPOUND ON THEIR EMPIRICAL FORMULA
NCl3 --> Nitrogen trichloride
IF7 --> Iodine heptafluoride
XeO4 --> Xenon tetroxide
How many grams of oxygen are present in 5.75 moles of Al2O3?
Grams= molar mass O3 * ratio moles element/compound * moles of compound
grams = 15.999 * 3/1 * 5.75
grams = 275.98275
Calculate molarity for 7.82 g of C10H8 in 85.2 mL of benzene solution
0.716109 M
What is the formula for molarity?
Molarity = moles/Volume