chem exam 1
the mass percent of Ca in CaSO4 os 29.45%. to calculate the mass of Ca present in a 25.6 g sample of this compound, the correct procedure is given by
(29.45/100) *25.6
which of the following gives the correct relationship between the decimal prefixes?
-1 mL= 1 * 10^3 microliters -10^9 nm = 1 m
Chlorine has two principal stable isotopes, 35 Cl (isotopic mass 34.9689) and 37 Cl (isotopic mass 36.9659). The atomic mass of Cl is 35.4527 amu. Which of the following options correctly describes these isotopes?
-35Cl has a greater abundance -the more abundant isotope comprises 75.774% of all stable Cl atoms
a useful method for keeping track of quantities in a chemical reaction is a reaction table. which of the following are components of a reaction table ? select all that apply
-a balanced chemical equation -final amounts of reactants and products remaining after the reaction -initial amounts of reactants and products before reaction -change in the amounts of reactants and products during the reaction
which of the following statements correctly describe how conversion factors are used in calculations?
-all units should cancel except for those required in the answer -conversion factors are relationships used to express the same quantity in different units -the conversion factor should be selected so that the units in the original quantity cancel with those in the conversion
naming oxoacids
-ate in the oxyanion is changed to -ite -ite in the oxyanion is changed to -ous HClO hypochlorite, hypochlorous acid HClO4 : perchlorate, perchloric acid
which of the following describes the three temperature scales and their relationship to one another
-both the kelvin and celcius have the same size degree unit (the starting points of the Celsius and Kelvin scale differ but 1K=1C) -absolute zero is 0K or -273.15 C -all temperatures on the Kelvin scale are positive (besides absolute zero)
which of the following steps are necessary to calculate the mass percent of oxygen in acetic acid (CH3COOH)?
-calculate the molar mass of acetic acid from its formula -multiply the moles of oxygen I the molecular formula by the molar mass of oxygen and then divide by the mass of one mole of acetic acid -multiply the answer by 100 to find the mass percent of oxygen in acetic acid
naming ionic compounds
-cation is named first and anion second -the name of the cation is the name of the metal -the anion has the suffix -ide added to the root of the nonmetal name -no prefixes are used when naming ionic compounds
which of the following correctly describe how conversion factors are used in calculations?
-conversion factors are relationships used to express the same quantity in different units -the conversion factor should be selected so that its units cancel with one of the units in the factor -all units should cancel except those needed in the answer when multiplying by a conversion factor
the number of entities in a mole is equal to ___ and is called _____
6.022 x 10^23 Avogadro's number
An unknown element has two isotopes : one whose mass is 68.926 amu (60% abundance) and the other whose mass is 70.925 (40% abundance). the average atomic mass of the element is equal to ________
69.73 (68.926*0.60)+(70.925 *0.40) =(41.36+28.37)= 69.73
The SI system is based on ____ fundamental units called base units. all other units are combinations of these fundamental units and are called ________
7 derived
what is the mass percent of oxygen in the aluminum oxide Al2O3?
47.08%
1 formula unit of KOH has a mass of ____ amu; hence 1 mol of KOH has a mass of ____ g
56.11 amu 56.11 g
farenheit
=1.8C + 32
Kelvin
=C + 273
mass fraction
=mass of element/total mass of compound
each element can be represented by an atomic symbol with the format AZ X. Match each component of this symbol with its correct meaning
A : mass number. the total number of protons and neutrons in the nucleus Z : atomic number : number of protons in the nucleus X : atomic symbol : the element symbol found on periodic table
tera
T trillion 1 * 10^12
which convention is used in this textbook for rounding off atomic masses based on the periodic table?
atomic masses are rounded to 4 significant figures
column of periodic table
group
nonmetal ion charges
group # - 18
ion charges of main group monoatomic ions
group 1 : +1 group 2 : +2 group 3 : Al3+ Ag : Ag+ Zn, Cd : 2+ group 15 : 3- group 16 : 2- group 17 : 1- group 18 : no common ions
accuracy
how close a measurement is to the known value -affected by systematic error
binary acids are named with the prefix ___ and the suffix ___
hydro- -ic example : hydrobromic acid
OH-
hydroxide
ClO-
hypochlorite
a chemical equation must be balanced. this means that the same ____and ____ of atoms must appear on both sides of the equation
number, type
pico
p trillionth 1 * 10^-12
ClO4 -
perchlorate
row of periodic table
period
MnO4 -
permanganate
O2 2-
peroxide
PO4 3-
phosphate
proton
positively charged particle found within the center of the atom
milli
thousandth 1 * 10^-3 0.001
mass number
total number of protons and neutrons
molecules
two or more atoms bonded together
compounds
two or more substances CHEMICALLY combined in a fixed proportion by mass -properties of the elements in compound are lost -cannot be separated by physical means
neutron
uncharged dense particle located in the center of the atom
homogenous
uniform composition throughout sample
percent by mass
( mass of element/total mass of compound ) * 100
Celcius
(F-32)/1.8
which of the following options gives the correct procedure to calculate the number of moles of a substance given the mass?
(given mass)/(molar mass) g of substance x mol/g = given mass/molar mass
which of the following provides the correct mathematical equation to convert the number of atoms of a sample to the number of moles
(number of atoms)/(avogadros number)
which of the following steps would be required to convert between the masses of any two substances involved in the same chemical reaction
-convert from the given mass to moles of the same substance -write a conversion. factor using the coefficients from the balanced equation, and convert to moles of the second substance -write a balanced chemical equation for the reaction-the first step should be to write a balanced equation, unless this information has already been provided
extensive properties
-dependent on the amount of substance -cannot be used to identify substance example : volume, mass, length, area, color
which of the following statements correctly describe the empirical formula for a compound
-different compounds can have the same empirical formula -the empirical formula of a compound gives the smallest whole number ratio of atoms in a compound
daltons atomic theory
-elements are composed of tiny, indivisible particles called atoms -all atoms of one element are alike in mass, size, and properties, but are different in mass, size and properties from atoms of another element -atoms combine in simple, numerical ratios to form compounds -chemical reactions occur when atoms re-organize to form different substances. the atoms themselves do not change
which of the following statements describe combustion analysis correctly
-every 1 mole of carbon in the compound will produce 1 mole of CO2 -combustion analysis involves burning a compound in O2 -the mass of hydrogen in the compound is determined from the amount of H2O produced
which of the following correctly describe how to name an ionic compound
-for a monatomic anion, the element name is changed to end in -ide -the cation is named first and the anion second
which of the following correctly describes how to determine the charge on a monatomic ion using the periodic table?
-for main group cations, the ion charge equals the A group number -Ca (calcium) is in group 2A and therefore forms the Ca2+ ion -the charge of most transition metal cations cannot be readily predicted from the periodic table
which of the following options correctly describe how to calculate a molecular or formula mass for a compound?
-in a formula such as Ca(NO3)2, all the numbers of atoms inside the parentheses must be multiplied by 2 because of the subscript -the formula/molecular mass is given by the sum of the masses of the component elements in the correct proportions -the atomic mass of a cation or anion Is practically the same as the mass of the neutral element
which of the following correctly describe isomers?
-isomers are compounds with the same molecular formula -isomers are compounds with the same empirical formula -isomers are compounds with the same molar mass
which of the following statements correctly describe the molecular formula for a compound
-it is possible that the molecular formula for a compound is the same as its empirical formula -the molecular formula gives the actual number of each type of atom in a compound -a molecular formula may give little or no information about the structure of the compound
the ___ formula of a compound is an integer multiple of the ___ formula
-molecular -empirical
which of the following statements correctly describe how units are treated in a mathematical calculation?
-quantities cannot be added or subtracted unless they have like units -like units can be cancelled by division -units can be multiplied or divided
precision
-range of measurements - how close they are to eachother -affected by random error
which of the following statements correctly describe the atomic number of an element?
-the atomic number is equal to the number of protons in the nucleus -each element has its own unique atomic number
consider the formula for the ionic compound Na2O. which of the following statements correctly interpret this formula?
-the compound contains 2 Na+ ions for every O2- ion -the cation in the compound is Na+
which of the following correctly describe the SI base quantities and their units?
-the correct abbreviation for kelvin is K -the SI unit for length Is meter -SI abbreviation for second is s
which of the following statements describe the information that can be gained from a balanced equation?
-the identities of substances involved -the physical states of reactants and products -the relative quantities in moles of substances involved
which of the following correctly describes the mass number of an element?
-the mass number is given as the sum of the protons and neutrons in the nucleus -the mass number is often written as a left superscript next to the atomic symbol -the mass number of an element is given by the symbol A
which of the following choices describe the steps required to determine the empirical formula of a compound from the mass %?
-the mass percentage of each element is converted to moles using the mass formula mass/molar mass -the ratio of atoms of each element must be a ratio of integer numbers -if a compound contains 52% of mass of C, it can be assumed that there are 52 g of C in 100 g of the compound
which of the following options correctly describe the limiting reagent in a reaction? select all that apply
-the maximum amount of product formed is the amount that can be formed from the limiting reagent -the limiting reagent limits the amount of product that can form
which of the following options correctly describe how to name a binary covalent compound?
-the name of the first element remains unchanged, except for the addition of a prefix where appropriate -the second element is named with its root and the suffix -ide -a greek numerical prefix is used to indicate the number of atoms of each element in the compound, except mono- is never used with the first element
which of the following correctly reflect avogadros number?
-the number of entities in a mole is called avogadros number -the mole contains 6.022 x 10^23 entities
which of the following correctly describe atomic structure?
-the number of protons equals the number of electrons in a neutral atom (for an atom to be neutral, the number of positively charged particles/protons must be equal to the number of negatively charged particles/neutrons -the nucleus comprises a very small fraction of the total volume of the atom -the protons and neutrons together comprise most of the mass of the atom
iodine trichloride is produced in a two step process, represented by the following balanced equations : I2 + Cl2 = 2ICl and Icl + Cl2 = ICl3 select all the statements that correctly describe how to write a complex balanced equation for the overall process
-the overall equation is given by I2 (s) + 3Cl2(g)=2ICl3(s) -the second equation must be multiplied by 2
which of the following statements correctly describe the steps used to determine which reactant in a given reaction is limiting? select all that apply
-the reactant that produces the least amount of possible product is the limiting reactant -calculate the amount of product that could be formed from each reactant -calculate the molar masses of any reactants for which a mass has been given
mixtures
-two or more substances physically mixed together -composition of mixtures is VARIED -properties of individual components are maintained -components can be separated by some physical; technique
which of the following statements correctly describe molar mass?
-when referring to the mass per mole of an entity, the term 'entities' could refer to atoms, ions, molecules, or formula units -the molar mass of a substance is the mass per mole of its entities -the periodic table can be used to calculate the molar mass of any substance
arrange the necessary steps in order for finding the molecular formula of an unknown compound from mass percent data
1. assume that the sample contains 100.0g of compound and express each mass percent as a mass in grams 2. convert the mass of each element to moles of each element 3. derive the empirical formula looking for the simplest whole number ratio of moles 4. divide the molar mass of the compound by the mass of the empirical formula in order to find a multiple that is an integer 5. multiply each subscript of the empirical formula by the integer multiple
correctly order the steps necessary to determine the molecular formula for a compound using combustion analysis data.
1. determine the masses of carbon and hydrogen from the masses of CO2 and H2O 2. determine the mass of oxygen, if present, by subtracting the masses of carbon and hydrogen from the total mass 3. determine the number of moles of each element in the compound and hence the empirical formula 4. determine the molecular formula using the empirical formula and molar mass
correctly order the steps necessary to calculate the mass of product formed in a chemical reaction, given the masses of all reactants.
1. determine the moles of each reactant present by dividing its mass by its molar mass 2. determine the amount of product that could be formed from each reactant using the appropriate mole ratios 3. identify the limiting reactant as the reactant that produces the least amount of product 4. to find the mass, multiply the number of moles of product formed (from the limiting reactant) by the molar mass of the product
list the steps in order for calculating the molar mass of nitrogen gas
1. identify that nitrogen exists as N2 and find the atomic mass of nitrogen on the periodic table 2. multiply the atomic mass of nitrogen by 2 in order to calculate its molecular mass 3. report the molar mass of nitrogen as 28.02 g/mol
rules for rounding off numbers
1. if the digit is more than five, the preceding number increases by 1 2. if the digit removed is less than 5, the preceding number is unchanged 3. if the digit removed is 5, the preceding number increases by 1 if it is ODD and remains unchanged if it is EVEN 4. be sure to carry two or more additional significant figures through a multistep calculation and round off only the final answer only
place the following calculations in the correct order to determine the molar mass of H2SO4
1. m of H2SO4= (2 * M of H)+((M of S)+(4*M of O) 2. (2*1.008g/mol)+(32.07g/mol)+(4*16.00g/mol) 3. M of H2SO4 = 98.09 g/mol
correctly order the steps necessary to balance a chemical equation
1. write a skeletal equation 2. balance the atoms 3. adjust coefficients such that they are the smallest whole number coefficients 4. do a final check to make sure equation is balanced
the atomic mass unit is defined as
1/12 the mass of a carbon-12 atom
given the balanced equation 3H2+N2=2NH3, calculate the mass of NH3 produced by the complete reaction of 2.55 g of H2
14.4 g 2.55 g H2 * (1mol H2/2.016 H2) * (2 mol NH3/3mol H2) * (17.03g NH3/1 mol NH3)
2.5 mm=
2.5 * 10^-6 km
2.5 cm =
2.5 * 10^4 micrometers
0.25 m =
2.5 * 10^8 nm
25 km =
25,000 m
a particle isotope of an element is represented by the symbol 36 17 Cl. the mass number of this isotope is equal to ______, and this number represents the total number of protons plus _____ in the nucleus. The atomic number of the isotope is equal to _______, and this number represents the number of ______ in the nucleus
36 neutrons 17 protons
metalloids
B, Si, Ge, As, Sb, Te look like metals, behave like nonmetals
hypobromite
BrO-
bromite
BrO2 -
bromate
BrO3 -
perbromate
BrO4 -
conversion from F to C
C = 5/9(F - 32)
conversion from K to C
C = K - 273.15
a compound has the empirical formula CH2O. what are the possible options for the molecular formula of the compound?
CH2O C6H12O6 C2H4O2
carbonate
CO3 2-
the correct formula for the compound dichloride pentoxide is
Cl2O5
conversion from Celsius to Fahrenheit
F=(9/5 * C) + 32
what is the empirical formula of a compound that consists of 0.039 moles of iron atoms combined with 0.052 moles of oxygen atoms
Fe3O4 0.052/0.039=1.33 which gives a ratio of 1:1.33. multiply by 3 to get two whole numbers = 3:4
giga
G billion 1 * 10^9
conversion from C to K
K = C + 273.15
mega
M million 1 * 10^6
permanganate
MnO4 -
the molecular formula of a compound having the empirical formula NH2 (m = 32.05 g/mol) is
N2H4
a nitrogen oxide contains 30.45% N mass. if the molar mass of the compound is 90 +/- 5 g/mol, what is the molecular formula?
N2O4
some covalent compounds are so common that they are named using common or 'trivial' names instead of systematic names. match the following
NH3 = ammonia H2O = water CH4 = methane
which of the following formulas for ionic compounds are written correctly?
NaNO3 Mg3(PO4)2 CaCO3
sulfite
SO3 2-
sulfate
SO4 2-
which of the following correctly describes a formula unit?
The simplest ratio representing the relative numbers of cations and anions in an ionic compound
atomic number of an element
number of protons in the nucleus
which of the following options correctly describe hydrated ionic compounds?
a greek prefix is used to indicate the number of H2O molecules per formula unit heating a hydrate can remove some or all of the water molecules a hydrate has a specific number of water molecules associated with each formula unit
law of definite composition
a particular compound is always composed of the same elements in the same fraction or percent by mass
an extensive property is defined as
a property that depends on the amount of substance present mass is an example of an extensive property
an intensive property is defined as
a property that is independent of sample size density is an example of an intensive property
which of the following options correctly describes how straight-chain alkanes are named?
alkanes are named with the root based on the number of carbon atoms followed by the suffix -ane
NH4+
ammonium
actual yield
amount of product obtained experimentally from a chemical reaction
isotopes are atoms of the same element that have the same ________ number but a different _______ number. this is because isotopes have the same number of protons but a different number of ________
atomic mass neutrons
C2H3O2 -
acetate
percent yield
actual yield/theoretical yield * 100
isotopes
atoms of an element with the same number of protons, but a different number of neutrons -isotopes have the same atomic number, but different mass number -all isotopes of the same element undergo the same types of chemical reactions
centi
c hundredth 1 * 10^-2 0.001
the atomic mass unit is a standardized unit defined as exactly 1/12 the mass of an ______________ -12 atom. the atomic mass (weight) of any element is determined relative to this standard and is not a whole number, since it is an _______ of the masses of its naturally occurring isotopes
carbon 12 atom average
CO3 2-
carbonate
when naming an ionic compound, the ____ is always named first. to name the anion, the root of the nonmetal name is added to the suffix _____. The anion O2- is therefore named ________
cation -ide -oxide
metals are alway
cations
ClO3 -
chlorate
ClO2 -
chlorite
the ionic compound CrCl3 is correctly named
chromium(III) chloride
heterogenous
composition of the mixture is not uniform throughout the sample
metals
conduct electricity malleable and ductile, have luster, mostly solids
which of the following are the correct names for ionic compounds?
copper(II) oxide potassium chloride
the term molecular mass can only be applied to a _____ compound since _____ compounds do not consist of molecules. the correct term that is applicable to all types of compounds is _____ mass
covalent ionic formula
CN-
cyanide
deci
d tenth 1 * 10^-1 0.1
nonmetals
do not conduct electric current not malleable or ductile, no luster mostly gases, fewer liquids and solids
molecular formula
element symbols with numerical subscripts to give the actual number of atoms of each element in a molecule
the mole relates the atomic mass of an element expressed in amu with the mass of 1 mole of that element expressed in _____. the mass of 1 mole of oxygen atoms is therefore equal to _____ g
grams 16
intensive properties
independent of the amount of substance -allows a scientist to identify the material -example : density, boiling pt, pH, flammability
the atomic mass ___ is used to define the atomic mass of elements that have very large variations in isotopic composition depending on their source
interval
Roman numerals are used in naming _______ compounds containing a metal that can form more than one ______. The Roman numeral specifies the charge on the metal
ionic cation
kilo
k thousand 1 * 10^3
which is the correct name of the ionic compound Li3N
lithium nitride
diatomic molecules : rule of 7
makes a 7 on the periodic table! N2 O2 F2 Cl2 Br2 I2
density is defined as the ratio of ________ to ______________ for a substance or sample
mass to volume
Hg2 2+
mercury (I)
micro
millionth 1 * 10^-6
in order to calculate the overall percent yield for a multistep process
multiply the individual percent yields by eachother
nano
n billionth 1 * 10^-9
electron
negatively charged particle
NO3 -
nitrate
NO2 -
nitrite
space filling model
shows an accurately scaled image of the molecule with spheres giving the relative size of the atoms, angles, and distance between nuclei
ball and stick model
shows the atoms as balls and the bonds as sticks with the angles between the bonds being accurate
structural formula
shows the relative placement and connections of atoms in a molecule with either pairs of dots for electrons or a line to represent the bonds
nucleus
small region that contains almost all of the mass of an atom
SO4 2-
sulfate
molar masses
take into account the prevalence (% abundance) of the isotope as well as the isotope mass
the measure of how hot or cold an object is relative to another is its _____ whereas _____ is the energy that flows between two objects
temperature heat
theoretical yield
the amount of product calculated from the molar ratio in the balanced chemical equation
multiplication and division with sig figs
the answer contains the same number of significant figures as the measurement with the fewest significant figures
addition and subtraction with sig figs
the answer will have the same number of decimal places as there are in the measurement with the fewest decimal places
what is the only additional information needed to calculate the empirical formula of a compound if the masses of each element of the compound are provided?
the molar mass of each element
