Flashcards in General Chemistry- Compounds and Stoichiometry Deck (112)
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?
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?
What do the letters represent in the conversion equation for Normality to Molarity?
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
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?
What is the percent composition?
The percent of a specific compound that is made up of a given element.
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.
What is a combination reaction?
Two or more reactants forming one product
What is a decomposition reaction?
The oppsoite of a combination reaction: a single reactant breaks down into two or more products, usually as a result of heating, high frequency radiation, or electrolysis.
What is an example of a reaction that utilizes high frequency light?
The decomposition of silver chloride in the presence of sunlight.
The ultraviolet component of sunlight has _______ to do with _____________.
The ultraviolet component of sunlight has sufficient energy to catalyze certain chemcial reactions.
What is a combustion reaction?
A special type of reaction that involves a fuel- usually hydrocarbon- and an oxidant (normally oxygen)
In its most common form, in the combustion reaction the reactants are what?
The reactants form the two products of carbon dioxide and water
What is a single-displacement reaction?
When an atom or ion in a compound is replaced by an atom or ion of another element.
What is a further classification of single-displacement reactions?
What is a double-displacement reaction?
Elements from two different compounds swap places with each other to form two new compounds.
What are other names for a double-displacement reaction?
Why does a double-displacement reaction occur?
When one of the products is removed from the solution as a precipitate or gas or when two of the original species combine to form a weak electrolyte that remains undissociated in solution.
What i a specific type of double-displacement reaction?
What is a neutralization reaction?
An acid reacts with a base to produce salt (and usually water)
What is added when the reaction of acids and bases are not visible?
Why must the reaction of a chemical equation be balanced?
To reflect the Laws of conservation of mass and charge.
What must be equal in a reaction equation?
The mass of the reactants consumed must be equal to the mass of products generated
What are stoichiometric coefficients?
The numbers placed in front of each compound
What are stochichiometric cofficents used for?
To indicate the relative number of moles of a given species involved in the reaction.
In general stoichemetric coeficients are given how?
As whole numbers
What is the most useful information gleaned from a balanced reaction?
The mole ratio of reactants consumed to products generated
What ratios can be generated using stoichiometric coefficients?
Generate the mole ratio of one reactant to another, or one product to another.
What is a limiting reagent?
The reactant, in a reaction, that will be used up or consumed first.
Why is it called a limiting reagent?
It limits the amount of product that can be formed in the reaction.
What are excess reagents?
The reactants that remain after all the limiting reagents are used up
What two principles should be kept in mind when dealing with problems involving limiting reagents?
All comparisons of reactants must be done in units of moles. Gram-to-gram comparisons will be useless and may even be misleading.
It is not the absolute mole quantities of the reactants that determine which reactant is the limiting reagent. Rather, the rate at which the reactanst are consumed, combined with the absulte mole quantities determines which reactant is the limiting reagent.
What is the yield of a reaction?
Refers to either the amount of product predicted or actually obtained when a reaction is carried out.
What is the theoretical yield?
The maximum amount of product that can be generated as predicted from the balanced equation, assuming that all of the limiting reactant is consumed, no side reactions have occurred, and the entire product has been collected.
What is usually never attained in regards to yield?
What is actual yield?
The amount of product one actually obtains during the reaction.
What is the percent yield?
The ratio of the actual yield to the theoretical yield, multiplied by 100 percent.
What is the equation for percent yield?
Percent yield = (actual yield/theoretical yield) x 100%
Why are ionic compounds of particular interest to chemists?
Because certain important types of chemical reactions--Acid-Base and oxidation-reduction reactions, for instance-- commonly take place in ionic solutions.
For stoichiometry problems, what is the goal with ions?
To identify oxidation states
For stoichiometry problems, what will finding the oxidations states allow us to determine?
Electron equivalents, balance equations, and deduce chemical formulas from nomenclature.
The rule of metals acting as cations and nonmetals as anions, does not always hold true for which elements?
Elements like hydrogen, which can act like an anion or cation but is still classified as a nonmetal.
Ionic compounds are held together by what?
Ionic bonds, which rely on the force of electrostatic attraction between oppositely charged particles
For elements (usually metals) that can ____________, the charge is indicated by ___________.
For elements (usually metals) that can form one positive ion, the charge is indicated by a Roman numeral in parentheses following the name of the element.
What is another less comonly used way to write an element with less and greater charge?
Add the ending -ous or -ic to the root of the Latin name of the element to represent the ions with lesser and greater charge
How are monatomic anions named?
Dropping the ending of the name of the element and adding -ide.
Polyatomic anions are usually called ________. Why?
Oxyanions, because Many polyatomic anions contain oxygen.
What happens when an element forms two oxyanions?
The name of the one with less oxygen ends in -ite, and the one with more oxygen ends in -ate.
In extended series of oxyganions, what prefixes are used? What do they indicate?
Hypo- and hyper written as per-, are used to indicate less oxygen and more oxygen
Polyatomic anions gain what? And are named how?
Polyatomic anions often gain one or more H+ ions to form anions of lower charge. Resulting ions are named by adding the word hydrogen or dihydrogen to the fron of the anion's name.
What is another/older method for naming the polyatomic anions?
Using the prefix bi- to indicate the addition of a single hydrogen ion.
What are some of the charaged atoms or molecules on the MCAT?
The active metals--the alkali metals (group IA or group 1) and the alkaline earth metals (group IIA or group 2), which have charges of +1 and +2, in the natural state.
Which atoms usually form anions?
Nonmetals-- all the halogens (group VIIA or group 17) form monatomic anions with a charge of -1 because they already have 7 electrons and aim to fill an octet.
All elements in the same group tend to form what?
Tend to form monatomic ions with the same charge.
What should be taken as a note when dealing with anionic species?
There are anionic species that contain metallic elements
What should be taken as a note for oxyanions of the halogens?
In the oxyanions of the halogens, such as ClO- and ClO2-, the halogen is assigned a positive oxidation state.
For nonrepresentative elements in regards to ions, there are numerous what?
Numerous positively charged states
What are examples of nonrepresentative elements in regards to ions?
What can be indicative of the oxidation state of a given element?
The color of a solution
An element can go through different oxidation states and thus under go what?
Different electron transition and therefore absorb different frequencies of light.
What is ionicity?
The same element in different oxidation states can undergo different electron transitions and therefore absorb different frequencies
Solid ionic compounds tend to be poor what?
Conductors of electricity because the charged particles are rigidly set in place by the lattice arrangement of the crystalline solid.
What allows for ions to conduct electricity?
If placed in aqueous solutions, because the lattice arrangement is disrupted by the ion-dipole interactions between the ionic compounents and the water molecules. the cations and anions are now free to move, and as a results, the solution of ions is able to conduct electricity.
What are electrolytes?
Solutes that enable solutions to carry currents
What governs the electrical conductivity of aqueous solutions of ions?
The presence and concentration of ions in the solution.
What varies in a electrolytic solution?
The number of electron equivalents being transferred in such a system, such as in electrochemical cells.
What solution is a very popular conductor?
Pure water, which has no ions other than the very few hydrogen ions and hydroxide ions that result from water's low-level autodissaciation.
What is solute?
The tendency of an ionic sulute to dissolve
When is a solute considered a strong electroylte?
If it dissociates completely into its constituent ions.
What are examples of strong electrolytes?
Ionic compounds: NaCl, and KI
Molecular compounds with highly polar covalent bonds that dissociate into ions when dissolved: HCl in water
When is a solute considered a weak electrolyte?
Electrolytes that ionixe or hydrolyzes incompletely in aqueous solution , and only some of the solute is dissolved into its ionic constituents.
What are examples of weak electrolytes?
acetic acid and other weak acids
Ammonia and other weak bases
What are nonelectrolytes?
Compounds that do not ionize at all in water, retaining their molecular structure in solution, which may also limit their solubility.
What are examples of nonelectrolytes?
Nonpolar gases and organic compounds: O2, CO2, Glucose