How can a mole be defined?
it can be defined in terms of the number of particles in a substance or by the grams of the substance
what is the mole?
the number of atoms of an elements equal to the number of atoms in exactly 12g of Carbon-12
how would you calculate the number of moles present in a given mass of a substance?
divide the mass of the substance by its molar mass
how would you calculate the number of particles present in a given number of moles of a substance?
multiply avagadros number by the number of moles
How would you calculate the number of particles present in a given mass of a substance?
take the given mass of the substance and divide it by the molar mass, and multiply the moles by Avagadros Number
because the actual mass of a single atom is so small what is used?
amu's are used to describe the mass of an atom
is knowing the mass of one atom or one molecule in atomic mass units important in a lab? Explain.
no, it isnt practical. instead the gram is the desired unit of mass
in order to establish the relationship between mass and grams what must scientists do?
1. identify what they already knew about atoms and mass
2. using the relationship between masses of different elements, they
what relationship did scientists discover between the masses of different elements?
as long as the mass of the elements aer in the same ratio as their atomic masses, there are equal numbers of atoms of each element.
why are amu's used to dscribe the mass of an atom/
because the actual mass of a single atom is so small
As far as the masses of the element samples are in the ___ ratio as their atomic masses, there are equal numbers of ___
a mole of any element is defined as what?
the number of atoms of that element equal to the number of atoms in exactly 12.0 grams of carbon
the mass ( in grams) of one mole of a substance is equal to what?
its atomic mass or formula mass in amu's
how can you determine the number of moles of atoms in a mole of molecules by doing what?
looking at the subscripts
one mole of an ionic compound contains how many formula units does it contain
6.02 x 10 23 formula units
what does the molar mass depend on?
particles, atoms, molecules or formula units that make up a substance
why is the mole the central unit in converting them amount of a substance from one measurement to another?
because a mole measures a mass, number of particles, volume of gas
if you know the number of moles in a substance how many particles are there?
6.02 x 10 23 times that number of moles
how do you find out how many molecules are in 2 moles of water
mutiply the n umber of molecules in one mole of water by 2.
what did avagadro say about gases?
at the same temperature and pressure, equal volumes of gas contain the same number of gas particles
the molar volume relationship can be used to convert between what?
the volume of that gas at STP, PRESSURE, NUMBER OF MOLES OF GAS
what is the percentage composition of compound? how do you find it?
it is the percentage by mass of each element in the compound. it is determined by dividing the mass of each element by the mass of the entire compound and multiplying by 100%
How can you find the empirical formula?
using the mass of each element and calculating the moles of each element then comparing mole ratios
how can the empirical formula ALSO be calculated?
caculated from the percentage composition of the compound
what is the molecular formula?
gives the actual number of atoms of each element in a molecular compound.
how can the molecular formula be calculated?
diving the molar mass of the compound by the empirical formula mass
what particles are you describing when you say a mole of hydrogen?
hydrogen atoms or hydrogen molecules because it is diatomic
For each of the following substances list the representative particle, number of particles in 1 mole, and the mass of one mole
4. Magnesium Oxide
1. atom, a.n, 20.2 g
2. molecule, a.n, 32 g
3. molecule, a.n,18 g
4. formula unit, a.m, 40.3 g
why is the mole the central unit in converting a substance from one measurement to another?
because the mole measures both a mass and a number of particles
you have a sample of sodium chloride with a mass of 11.2 grams, how many moles of sodium chloride are in this?
-1 mole of NaCl has a mass of 58.5 grams
- 112 g NaCl x 1 mole NaCl
58.5 g NaCl
= .191 mole of NaCl
what did avagadro propose about gases?
he said that at the same temperature and pressure, equal volumes of gases contain the same number of gas particles
the volume of a gas is known as what?
molar volume because it is the volume of one mole of gas at standard conditions
the formula for a compound indicates what?
the number and kind of each atom in a representative particle of the compound
what is the percentage composition of a compound?
the mass of each element in a compound compared to the entire mass of the compound and multiplied by 100
what are the two ways in which you can find percent composition?
1. from the given formula, you take the amount of each element, divide by its atomic mass then times 100
2. experimental analysis.
a sample of an unknown compound with a mass of 0.2370g is extracted from the roots of a plant. decomposition of the sample produces 0.09480 g of C, 0.1264 g of O, and 0.0158 g of H. what is the percent composition of the problem?
-Determine the percentage of each element in the compound
C= 0.0948g/ 0.2370g x 100%
O= 0.1264g/0.2370g x 100%
H= 0.0158g/0.2370g x 100%
the ratio of atoms will be what?
the ratio of atoms will be the simplest whole number ratio of atoms of the elements in a compound
a compound was analyzed and found to contain 13.5 g of Ca, 10.8 G of O, and 0.675 g of H. what is the empirical formula for the compound?
- convert the mass of each element to the number of moles using molar mass
13.5 g Ca x 1 mol / 40.08 g
= 0.337 mol Ca
10.8g O x 1 mole O/ 16.0 g O
= 0.675 mol O
0.675g H x 1 mol H/ 1.01g H
= 0.668 mol H
- divide each by the smallest number of moles
0.337mol Ca/0.337 = 1 mole of Ca
0.675 mol O/0.337 = 2.00 mol O
0.668 mole H/ 0.337= 1.98 mol H
the mole ratio of the elements is ..
1Ca: 2O: 2H
the empirical formula is
what does the empirical formula of a compound indicate? what doesnt it tell?
the simplest ratio of atoms in the compound, but it doesnt tell the actual number of atoms in each molecules
the exact number of atoms in each molecule of a compound determines what?
determines the properties, or characteristics of that compound
ribose has a molar mass of 150g/mole and a chemical composition of 40.0% C, 6.67% H, and 53.3% O. what is the molecular formula for ribose?
1. find the empirical formula
40%C: 40g x 1 mol C/ 12 g C
= 3.33 moles of Carbon
6.67% H: 6.67g x 1 mol H/ 1 g H
= 6.60 moles of Hydrogen
53.3%O: 53.3g x 1 mol O/16g
= 3.33 moles of Oxygen
mole ratio: 1 molC: 2molH: 1 molO
empirical formula mass: 30.0g/mol
empirical formula mass
150g/mole/ 30g/mole = 5
molecular formula= 5 x empirical
how many particles would 1 mole of CO2 contain? what would its volume be? what would its molar mass be?
6.02 x 10 23, 22.4 liters, 44.0 grams