quimica TEST #1 CHAPTER 3 Flashcards
The formulas mass of a substance is the:
Covalent substances exist as :
The formula mass of a covalent substance may be correctly referred to as a
the sum of the average atomic masses of all the atoms in the substance’s formula.
as discrete molecules.
as a molecular mass.
que es molecular mass
sumar los atomic masses de cada elemento en el compound
formula mass for ionic compounds
Ionic substances are composed of :
Ionic compounds do NOT exist as
The formula mass for an ionic compound may NOT correctly be referred to:
The average atomic masses of the ions can be approximated to be the same as the :
diff between ioinc compound and covalent substance
of discrete cations and anions combined in ratios to yield electrically neutral bulk matter.
as molecules.
as a molecular mass.
the average atomic masses of the neutral atoms.
The mole is an amount unit similar to familiar units like pair, dozen, gross, etc.
The mole is defined as the:
The mole provides a link between the:
the amount of a substance containing the same number of discrete entities (such as atoms, molecules, or ions) as the number of atoms in a sample of pure carbon-12 weighing exactly 12 g.
mass of a sample and the number of atoms, molecules, or ions in that sample.
The number of entities composing a mole has been determine to be:
This constant is named after Italian scientist _____________ and is known as ______________.
Avogadro’s Number (NA) =
The masses of 1 mole of different elements, however, are different, since the:
6.02214179 x 10^23.
This constant is named after Italian scientist Amedeo Avogradro and is known as Avogadro’s Number.
Avogadro’s Number (NA) = 6.022 x 1023
since the masses of the individual atoms are drastically different.
The molar mass of an element (or compound) is :
The molar mass of any substance is numerically equivalent to its:
Example:
A single 12C atom has a mass of 12 amu.
A mole of 12C atoms have a mass of 12 g.
the mass in grams of 1 mole of that substance, a property expressed in units of grams per mole (g/mol).
atomic or formula mass in amu.
molar mass es g/mol and formula mass en amu
calculations
The relationships between formula mass, the mole, and Avogadro’s number can be applied to compute various quantities that describe the composition of substances and compounds.
to find moles
mass in grams divided by molar mass
to find mass
moles x molar mass
how to find number of atoms
mass divided by molar mas = moles
moles x avogrado’s number = number of atoms
Given that saccharin has a molar mass of 183.18 g/mol, how many saccharin molecules are in a 40.0-mg (0.0400-g) sample of saccharin?
How many carbon atoms are in the same sample?
Percent composition -
Example: A 10.0 g sample of a compound is determined to contain 2.5 g hydrogen and 7.5 g carbon.
The percentage by mass of each element in a compound.
For compounds of known formula, the percent composition can also be derived from:
the formula mass and the atomic masses of the constituent elements.
ver vid de sacar percent composition from formula mass
A compound’s empirical formula can be determined from :
1)
2)
3)
from the masses of its constituent elements.
1)Convert element masses to moles using molar masses.
2) Divide each number of moles by the smallest number of moles.
3) If necessary, multiply by an integer, to give the smallest whole-number ratio of subscripts.
A compound’s empirical formula can be determined from:
1)
2)
3)
4)
from its percent composition.
1) Convert percent composition to masses of elements by assuming a 100 g sample of compound.
2) Convert element masses to moles using molar masses.
3) Divide each number of moles by the smallest number of moles.
4) If necessary, multiply by an integer, to give the smallest whole-number ratio of subscripts.