Chapter 4: Compounds And Stoichiometry Flashcards
What is a molecule?
A molecule is a combination of two or more atoms held together by covalent bonds.
How many moles are in 9.53 g of MgCl2?
What is the molecular weight of SOCl2? How many grams of SOCl2 equals one mole?
What is the weight of one carbon atom?
What are the units of molarity?
The units of molarity are mol/L
Calculate the molar masses of:
NaBr
SrCl2
C6H12O6
What is the pattern for dividing by nines?
1/9=.111
2/9=.222
3/9=.333
6/9=.666
Etc.
This is important to know for MCAT, won’t have a calculator.
What is 1/8? Quickly calculate any of the eights fractions.
1/8=0.125
3/8=0.375
5/8=0.625
7/8=0.875
What is the number of moles in 100g of each of the following:
NaBr
SrCl2
C6H12O6
How do the number of molecules in 18 g H2O compare to the formula units of 58.5 g NaCl?
Both values equal one mole of the given substance. The number of entities in a mall is always the same, equal to Avogadro’s number (NA=6.02x10-23 things)
What is the formula unit in chemistry?
Formula unit simply means the smallest repeating unit of a compound.
Determine the normality of the following solutions (note the species of interest is H+):
0.25 M H3PO4
95 g PO4 3- in 100ml of solution
What is molecular weight?
Molecular weight is the sum of the atomic weight of all the atoms in a molecule and its units are atomic mass units per molecule.
What is formula weight?
Formula weight of an ionic compound is found by adding up the atomic weights of the constituent ions, according to its empirical formula, and its units are also AMU per molecule.
What is a mole?
A mole is a quantity of any substance (dollars, kittens, atoms, molecules, particles, golf balls, socks, etc) equal to the number of particles that are found in 12 g of carbon-12 (12 6 C)
This number of particles is defined as Avogadro’s number (6x10-23/mol).
One molecule of carbonic acid has a mass of 62 AMU. What is the mass in grams per mole of carbonic acid?
Since one molecule of carbonic acid has a mass of 62 AMU, there are 62 g of carbonic acid per mole of carbonic acid.
What is molar mass?
The mass of one mole of a compound is called molar mass and is usually expressed in g/mol.
What are the units of molecular weight?
The units of molecular weight are
AMU/molecule.
Does molecular weight equal molar mass?
Molecular weight is amu/molecule. Molar mass is g/mol. So molecular weight does not equal molar mass.
What is the formula for determining the number of moles of a sample substance?
Moles= mass of sample (g) /
molar mass(g/mol)
What is the concept of equivalents?
Equivalents asks the question: how many moles of the thing we are interested in (protons, hydroxide ions, electrons, ions) will one mole of a given compound produce?
For example. Sodium will donate one mole of electrons (one equivalent), but magnesium will donate two moles of electrons (two equivalents).
Another example. One mole of HCl will produce one mole of hydrogen ions (H+), whereas one mole of sulfuric acid (H2SO4) donate two moles of hydrogen ions and one mole of SO4 2-. Therefore to gather one mole of hydrogen ions for a particular acid-base reaction, we could use one mole of HCl, a half mole of sulfuric acid (H2SO4) or a 1/3 mole of phosphoric acid (H3PO4).
Compare and contrast molar equivalents and gram equivalents.
Equivalents are equivalents. A molar equivalent would be asking how many moles of a given substance for an equivalent mole of a given substance. (One mole HCL will produce one mole of H+)
Whereas gram equivalents are mass calculations rather than mole units.
For example. Just as one mole of HCL will donate one mole of hydrogen ions, a certain mass of HCL (36.5 g) will also donate one equivalent of hydrogen ions. This gets us to the concept of gram equivalent weight.
What is gram equivalent weight and how can it be calculated? Knowing the equation is useful, understanding what the equation means is important.
Gram equivalent weight is an an amount of a compound, measured in grams, that produces one mole of the particles of interest.
Gram equivalent weight= Molar mass/n
Where n is the number of particles of interest produced or consumed per molecule of the compound in the reaction.
For example. One would need 31 g of H2CO3 (molar mass = 62 grams) to produce one equivalent of hydrogen ions because each molecule of H2CO3 donate to hydrogen ions (n=2).
Molar mass HCL is 36.5 g/mol. How many grams would you need for one equivalent of hydrogen ions? You need 36.5 grams of HCL to produce one mol of H+.
If the amount of a compound in a reaction is known, and we need to determine how many equivalents are present, how would you calculate that? Talk about it.
Equivalents= mass of compound (g)
gram equivalent weight (g)
If you had the mass a compound you could calculate the gram equivalent weight (molar mass/n) and come up with the equivalents.
Example that I made up:
What is normality (N)?
Normality is a measure of concentration in units of equivalents/L. Normality always assumes that the reaction will proceed to completion.
1 N solution of acid contains a [H+] equal to one mol/L.
2 N solution of acid contains a [H+] equal to two mol/L.
What is the conversion between molarity and normality?
Molarity = Normality / n
Where n is the number of protons, hydroxide ions, electrons, or ions produced or consumed by the solute.
Dimensional analysis of equivalent weight, equivalents, gram weight equivalents, and normality.
What is the gram equivalent weight of sulfuric acid?
Gram equivalent weight = molar mass / n
What is the normality (N) of a 2M Mg(OH)2 solution?
Couple things here to recognize:
Should know equation for molarity: molarity= normality/n
Also remember while you’re at it, normality = equivalents/L
n is the equivalence (using H2SO4 as the example, it produced 2 thingies of interest (in this case hydroxide ions) per mole).
What is the Colebrook titration graph of equivalents of carbonic acid?
Carbonic acid, H2CO3, is diprotic, meaning it has two protons to produce per molecule and therefor will take sufficient equivalent of base to dissociate the protons. I call this the Colebrook titration graph of carbonic acid because he likes it or something.
Calculate multiples of 16 up to 9.
16
32
48
64
80
96
112
128
144
Find the percent composition by mass of sodium, carbon, and oxygen in sodium carbonate Na2CO3
I will need to use approximations for calculations to get values that are close to the answers found in the multiple choice of the MCAT.
Actual values are:
Na: 43.4%
C: 11.3%
O: 45.3%
Experimental data from the combustion of an unknown compound indicates that it is 28.5% iron, 24% sulfur, and 49.7% oxygen by mass. What is its empirical formula?
Start by assuming a 100 g sample, which represents 28.5 g iron, 24 g sulfur, and 49.7 g oxygen. Next, divide each number of grams by the atomic weight to determine the number of moles.
After determining the number of moles, find the multiplier that gives all three compounds into your values of moles. These integer values will give you an empirical formula.
What are some similarities and differences between molecular and empirical formulas?
Both molecular and empirical formulas contain the same elements in the same ratios.
They differ in that molecular formulas give the actual number of atoms of each element in the compound, empirical formulas give only the ratio and therefor may or may not give the actual number of atoms.
What is the law of constant composition?
Bonus calculation, calculate percent composition of hydrogen and oxygen in water.
The law of constant composition states that any pure sample of a given compound will contain the same elements in an identical mass ratio.
For example, every sample of water will contain two hydrogen atoms for one oxygen atom. In terms of mass, for every one gram of hydrogen there will be 8 g of oxygen.
What is percent composition and how do you calculate it?
The percent composition of an element, mass, is the percent of a specific compound that is made up of a given element. The formula is as follows:
%comp=mass of element/molar mass x 100
What is the percent composition of chromium in K2Cr2O7?
What are the empirical and molecular formulas of a carbohydrate that contains 40.9% carbon, 4.58% hydrogen, and 54.52% oxygen and has a molar mass of 264 g/mol?
How to calculate.
Gather molar masses of constituents.
Assume 100g sample to calculate ratios based on molar masses of constituents.
Extrapolate empirical formula by finding the simplest whole number among the ratios.
Find the molar mass of the empirical formula.
Take the given molar mass and divide it by empirical molar mass to get a multiplication factor for the empirical formula.
Multiply the factor by the empirical formula to calculate the molecular formula.
What is a combination reaction?
A combination reaction has two or more reactants forming one product.
What is a decomposition reaction?
Decomposition reaction is the opposite 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.
The example equation is silver chloride being exposed to sunlight and producing silver crystals and chlorine gas.
What is a combustion reaction?
A combustion reaction is a special type of reaction that involves fuel, usually a hydrocarbon, and an oxidant, normally oxygen.
The example equation is a simple hydrocarbon of methane reacting with oxygen to produce carbon dioxide and water.
What is a single displacement reaction?
A single displacement reaction occurs when an atom or ion in a compound is replaced by an atom or ion of another element.
The example uses solid copper metal displacing silver ions in a clear solution of silver nitrate to form a blue copper nitrate solution and solid silver metal.
What is a double displacement reaction (another name for double displacement reactions is metathesis reactions)?
What are the products of a double displacement reaction (not molecular products, types of products)?
In double displacement reactions elements from two different compound swap places with each other to form two new compounds.
This type of reaction occurs when one of the products is removed from the solution as a precipitate or gas or two of the original species combined to form a weak electrolyte that remains dissociated in solution.
For example, when solutions of calcium chloride and silver nitrate are combined, insoluble, silver chloride forms in a solution of calcium nitrate.
What are the products of the reaction of zinc nitrate and sodium hydroxide?
Zn(NO3)2 + NaOH
This is a double displacement reaction and produce zinc hydroxide and sodium nitrate solution.
What are the products of the reaction of zinc nitrate and sodium carbonate?
Zn(NO3)2 + Na2CO3
This is a double displacement reaction, producing zinc carbonate, and sodium nitrate.
What is a neutralization reaction?
Neutralization reactions or a specific type of double displacement reaction in which an acid reacts with the base to produce a salt and usually water.
An example would be the reaction of hydrochloric acid with sodium hydroxide.
Complete and classify the most likely reactions in the table
Exercise in balancing an equation.
Balance the following:
How many grams of calcium chloride are needed to prepare 71.7 g of silver chloride according to the following equation?
Question on page 141
What is yield? What is theoretical yield? What is actual yield? What is percent yield?
Yield of a reaction is either the amount of product predicted or actually obtained.
Theoretical yield is the maximum amount of product that can be generated as predicted from the balance equation, assuming that all of the limiting reactant is consumed, no side reactions have occurred, and the product has been collected.
Actual yield is the amount of product one actually obtains during reaction.
Yield is the ratio of the actual yield to the theoretical yield multiplied by 100%.
What is the percent yield for a reaction in which 28 g of copper is produced by reacting 32.7 g of zinc in excess copper sulfate solution?
MCAT concept check 4.5 page 142
Question 4 page 142
For elements (usually metals) that can form more than one positive ion. What is the nomenclature for such positive ions? What are some examples?
What is the older, less commonly use method for naming these ions?
For elements that can form more than one positive ion the charge is indicated by a Roman numeral in parentheses following the name of the element.
The other method is adding -ous and -ic.
For example:
How are mono atomic anions named?
Monoatomic ions are named by dropping the ending of the name of the element and adding -ide.
For example:
When an element forms two oxyanions, the name of the one with less oxygen ends in (blank), and the one with more oxygen ends in (blank. Examples?
When an element forms two oxyanions, the name of the one with less oxygen ends in -ite, the one with more oxygen ends in -ate.
For example:
Extended series of oxyanions exist. Oxyanions could have 1, 2, 3, 4 oxygen. There is a naming system. What is that naming system?
Hypo- and per (for hyper) are used as suffixes for oxyanions with less oxygen or more oxygen, respectively.
For example:
Polyatomic anions often gain one or more hydrogen ions to form anions of lower charge. How are those resulting ions named?
There is an older, less common method. What’s that one?
The resulting ions created by gaining one or more hydrogen ions to form an ion of lower charge are named by adding the word hydrogen, or dihydrogen to the front of the anions name.
The older less common method uses the prefix bi- to indicate the addition of a single hydrogen ion.
For examples:
There are eight common polyatomic ions listed in the book that have unique names. What are they, what is their charge, and what is their name?
This card needs to be written until memorized, and after that you can delete this sentence from your card.
There are eight step wise rules for determining oxidation number, listed in priority. What are those eight steps?
1 in a neutral compound, all oxidation numbers add up to zero.
2 in an ion, all oxidation numbers must add up to the charge of the ion.
3 free elements have oxidation number of zero
4 fluorine is always -1
5 The group number generally dictates an oxidation number (group 1A = +1, IIA = +2,
III A = +3).
6 hydrogen with nonmetals is +1, hydrogen with metals is -1.
7 Oxygen is usually -2 (except with fluorine and peroxides)
8 Group VA is -1, VI A is -2, VII A is -3
How can you think of solving for oxidation states being an algebraic equation?
You can set up an algebraic equation to solve for oxidation states such as (image), whereas the equation equals the charge of the ionic compound, the unknown oxidation state would be X, and using the step wise rules of oxidation you can solve for X.
What is one way to qualitatively determine the oxidation state of a given element in a solution (generally transition metals). Why?
Don’t need to memorize oxidation states of transition metals, don’t need to memorize colors associated with the oxidation states. Just need to know what said in the answer.
The color of a solution can be indicative of the oxidation state of a given element in solution. The same element in different oxidation states can undergo different electron transitions, and therefore absorb different frequencies of light.
The image shows the different colors of oxidation states of plutonium.
Label the following solutions as electrolytes or non-electrolytes. Assume these compounds are all in aqueous solution.
Identify the following ions as cations or anions, and then provide the formula or chemical symbol.
