chem ch. 7
how many molecules of H2S are present in 7.53 g of H2S? how many atoms of H are present in the sample?
1.33 x 10^23 molecules H2S 2.66 x 10^23 atoms H
how many molecules of H2O2 are there in 0.759 g of the compound?
1.34 x 10^22 molecules H2O2
what is the mass of 3.45 mol of Li2O?
103. g Li2O
One mole
6.022 x 10^23
how many moles of lead does 15.0g of Pb represent?
7.24 x 10^-2 mol Pb
Calc the percent composition of K2S
70.90% K 29.10% S
What is the molar mass of aluminum hydroxide? Al(OH)3
78.00g
aluminum chloride forms by reaction of 13.43 g of Al with 53.18g of chlorine. what is the % composition of Cl in the compound?
79.8%
what is the mass of 1.05 mol of Ag?
113.0g Ag
to get a whole number, ____ the decimal by the corresponding number in the _____ of the fraction
multiply ; denominator
calculating the molecular formula from the empirical formula
n= molar mass/ mass of empirical formula = number of empirical units in the molecular formula
empirical formula
smallest whole number ratio of atoms in a compound
Molar Mass
the atomic mass of an element or compound (in grams) which contains Avogadro's number of particles
Molar mass is the ___
total mass (100%) of a compound
propylene contains 14.3% H and 85.7% C and has a molar mass of 42.08G. what is the molecular formula
(CH2)3 = C3H6
calc the molecular formula for a compound that contains 80.0% C and 20.0% H with a molar mass of 30.00g
(CH3)2 = C2H6
a compound with the empirical formula NH2 was found to have a molar mass of 32.05g. what is the molecular formula?
(NH2)2 = N2H4
a compound with eh empirical formula NO2 was found to have a molar mass of 92.00g. what is the molecular formula?
(NO2)2 = N2O4
how many moles of TiCl4 are there in 12.5g of titanium (IV) chloride?
0.0659 mol TiCl4
Avogadros conversion factor
1 mol / 6.022 x 10^23 or 6.022^23/ 1 mol
two step strategy for percent composition from experimental data
1. calc the mass of the compound formed 2. divide the mass of each element by the total mass and multiply by 100
Two step strategy for % composition of a compound
1. calc the molar mass of the compound 2. divide the total mass of each element by the compounds molar mass and multiply by 100
% composition can be determined by :
1. knowing the compounds formula or 2. using experimental data
to calc empirical formula you need to know:
1. the elements present in the compound 2. the atomic masses of each element 3. the ratio (by mass or %) of the combined elements
How many moles of mercury does 23.0g of Hg represent?
1.15 x 10^-1 mol Hg
how many Hydrogen atoms are in 1.00 moles of H2 molecules?
1.20 x 10^24 atoms H2
calc the empirical formula for a compound that contains 2.233g Fe and 1.926 g S?
2.000 Fe 3.000 S Fe2S3
calc the empirical formula for a compound that contains 11.19% H and 88.79% O
2.000 H 1.000 O H2O
calc the empirical formula for a compound that contains 56.68% K, 8.68% C and 34.73% O
2.000 K 1.000 C 3.000 O K2CO3
what is the mass of 2.13 x 10^18 atoms of Li?
2.46 x 10^-5 g Li
what is the mass of 8.21 mol of K?
321.0 g K
what is the mass of 1.28 x 10^8 atoms of Ne?
4.29 x 10^-15 g Ne
How many moles of NaCl are there in 253g of NaCl?
4.33 Mol NaCl
how many sulfur atoms are in 2.27 mol of S8 molecules?
4.82 x 10^24 atoms S8
How many Au atoms are contained in 16.0g of Au?
4.89 x 10^22 atoms Au
Find Molar mass of CaF2
40.08g + 2(19.00) g = 78.08g
calc the % composition of K2CrO4
40.27% K 26.78% Cr 32.95% O
what is the mass of 1.23 mol of PH3?
41.8 g PH3
when heated in air, 1.63 g of Zn reacts with 0.40g of oxygen to give ZnO. calc the % composition of the compound formed
80.3% Zn 20.% O
how many Ti atoms are contained in 7.80 g of Ti?
9.81 x 10^22 atoms Ti
calc the percent composition of O in H2O2
94.06% O
% composition is _____ of sample size
INDEPENDENT
Percent Composition
Mass percent of each element in a compound
The ______ _______ of a compound is equal to the ____ of the molar masses of the atoms in the molecule
Molar mass ; equal
Standard unit of measurement for chemistry
Mole
Molar Mass (MM)
mass of one mole of the formula unit of a compound
molecular formula
actual formula of a compound; represents the total number of atoms in one formula unit of the compound
The mole
individual atoms are tiny and have such a small mass, more convenient units for atoms are needed to be useful on the macro scale
