General Chemistry- Compounds and Stoichiometry Flashcards
What are compounds?
Pure substances composed of two or more elements in a fixed proportion.
How can compounds be broken down?
Compounds can be broken down by chemical means
What do broken down compounds produce?
Compounds produce their constituent elements or other compounds.
How are compounds characterized?
They are characterized by describing their physical and chemical properties.
What is a molecule?
A combination of two or more atoms held together by covalent bonds.
Molecules are what to compounds?
The smallest units of compounds that display their identifying properties
What can molecules be composed of?
Two or more atoms of the same element
Atoms of different elements
Measurements of compounds is usually done with what?
Moles or grams
Using molar mass to interconvert between the units
What does not form a true molecule? Why?
Ionic compounds do not form true molecules because of the way in which the oppositely charged ions arrange themseves in the solid state
What is a formula unit?
The empirical formula of a compound
Why is the term formula weight used?
Because no molecule actually exists, molecular weight becomes meaningless, so formula weight is used instead.
What is molecular weight?
The sum of the atomic weights of all the atoms in a molecule
What units are used for molecular weight?
Atomic mass units (AMU) per molecule
How is the formula weight found?
Adding up the atomic weights of the constituent ions according to its empirical formula.
What units are used for formula weight?
Atomic Mass Units (AMU) per molecule
One mole of a compound has a mass in grams equal to what?
1 mole of a compound has a mass in grams equal to the molecular or formula weight of the compound in AMU
What is molar mass?
The mass of one mole of a compound
What units are used to describe molar mass?
(g/mol)
What is the equation for determining the number of moles of a sample substance?
Moles= Mass of sample (g)/Molar mass (g/mol)
Which equation is usually used in stoichiometry and titration problems?
The formula for determining the number of moles of a sample
What is the concept of equivalents?
How many moles of the thing we are interested in (protons, hydroxide ions, electrons, ions…) will one mole of a given compound produce
How many equivalents will sodium donate?
one mole of electrons (one equivalent)
How many equivalents will magnesium donate?
Two moles of electrons (two equivalents)
What is the gram equivalent weight?
The amount of a compound, measured in grams, that produces one equivalent of the particle of interest.
What equation is used to calculate the gram equivalent weight?
Gram equivalent weight= Molar mass/n
What do the words/letters represent in the equation for gram equivalent weight?
Gram equivalent weight= Molar mass/n
n: the # of particles of interest produced or consumed per molecule of the compound in the reaction.
What is the simplified version for explaining the equivalent weight?
The mass that provides one mole of the particle of interest.
What equation is used to determine the number of equivalents that are present, if the amount of a compound in a reaction is known?
Equivalents= Mass of compound (g)/ (Grams equivalent weight (g))
What is normality?
(N) is a measure of concentration, given in the units equivalents/L
On the MCAT, what is normality normally used for?
Hydrogen ion concentration.
What is an example of normality used for hydrogen ion concentration?
A 1N solution of acid contains a concetration of hydrogen ions equatl to 1 mole per litter.
A 2N solution of acid contains a concentration of hydrogen ions equatl to 2 moles per liter.
What is the conversion equation from normality to molarity?
Molarity= Normality/n
What do the letters represent in the conversion equation for Normality to Molarity?
Molarity= Normality/n
n: the # of protons, hydroxide ions, electrons, or ions produced or consumed by the solute
What are the benefits of using equivalents and normality?
It allows a direct comparison of the quantities of the entity we are most interested in.
What is the Law of Constant Composition?
Any pure sample of a given compound will contain the same elements in an identical mass ratio.
What are two ways to express the formula of a compound?
The empirical formula
Molecular formula
What does the empirical formula give information on?
The simplest whole-number ratio of the elements in the compound
What does the molecular formula give information about?
The exact number of atoms of each element in the compound and is a multiple of the empirical formula
Can the empirical and molecular formula ever be the same for a compound?
Yes, sometimes they are identical.
Which ionic compounds will only have empirical formulas?
NaCl
CaCO3
What is the percent composition?
The percent of a specific compound that is made up of a given element.
(by mass)
What formula is used to determine percent composition?
Percent composition= (Mass of element in formula/molar mass)x 100%
The percent composition of an element can be calculated by using which “mass of elements in formula” formula?
The empirical or molecular formulas
What can be determined given both the percent compositions and molar mass of a compound?
The molecular formula given both the percent compositions and molar mass of a compound.