Stoichiometry and Analytical Chemistry - MCAT Chemical and Physical Foundations of Biological Systems
Card 1 of 420
Which of the following answer choices is not written as an empirical formula?
Which of the following answer choices is not written as an empirical formula?
Tap to reveal answer
An empirical formula must be written as the most simplified ratio of the elements that the compound contains. For example, 
is empirical because it cannot be simplified any further; the ratio of its atoms is 1:1:4.
The formula for glucose, 
, can be simplified by a factor of six. The empirical formula for glucose would be 
.
An empirical formula must be written as the most simplified ratio of the elements that the compound contains. For example,
The formula for glucose,
← Didn't Know|Knew It →
A researcher performs an elemental analysis on a compound. He finds that the compound is made up of only carbon, hydrogen, and oxygen atoms. He isolates a pure sample of the compound and finds that this sample contains 
of carbon, 
of hydrogen, and 
of oxygen. The researcher wants to perform further analysis on this compound the next day. Before leaving the lab the researcher creates three stock solutions of varying concentrations of this compound: 
(solution A), 
(solution B), and 
(solution C). He stores these solutions overnight at a temperature of 
.
Molecular weight of this compound = 
What is the empirical formula of this compound?
A researcher performs an elemental analysis on a compound. He finds that the compound is made up of only carbon, hydrogen, and oxygen atoms. He isolates a pure sample of the compound and finds that this sample contains
Molecular weight of this compound =
What is the empirical formula of this compound?
Tap to reveal answer
The first step in solving this question is to convert the mass of each element to moles. This can be done by dividing the given mass of each element by the molecular weight of each element.
The molecular weight of carbon is 
, hydrogen is 
, and oxygen is 
.
The first step in solving this question is to convert the mass of each element to moles. This can be done by dividing the given mass of each element by the molecular weight of each element.
After finding the moles of each element, you have to find the smallest whole number ratio of each element. The smallest whole number ratio can be found by dividing moles of each element by the lowest mole quantity (in this case, 
of oxygen).
You are left with 
carbons, 
hydrogens, and 
oxygen. The empirical formula for this compound is 
.
The first step in solving this question is to convert the mass of each element to moles. This can be done by dividing the given mass of each element by the molecular weight of each element.
The molecular weight of carbon is
The first step in solving this question is to convert the mass of each element to moles. This can be done by dividing the given mass of each element by the molecular weight of each element.
After finding the moles of each element, you have to find the smallest whole number ratio of each element. The smallest whole number ratio can be found by dividing moles of each element by the lowest mole quantity (in this case,
You are left with
← Didn't Know|Knew It →
A researcher performs an elemental analysis on a compound. He finds that the compound is made up of only carbon, hydrogen, and oxygen atoms. He isolates a pure sample of the compound and finds that this sample contains of carbon, of hydrogen, and of oxygen. The researcher wants to perform further analysis on this compound the next day. Before leaving the lab the researcher creates three stock solutions of varying concentrations of this compound: (solution A), (solution B), and (solution C). He stores these solutions overnight at a temperature of 
.
Molecular weight of this compound =
Compared to the empirical formula, the molecular formula contains more atoms of carbon and more atoms of oxygen.
A researcher performs an elemental analysis on a compound. He finds that the compound is made up of only carbon, hydrogen, and oxygen atoms. He isolates a pure sample of the compound and finds that this sample contains
Molecular weight of this compound =
Compared to the empirical formula, the molecular formula contains more atoms of carbon and more atoms of oxygen.
Tap to reveal answer
The first step in solving this question is to convert the mass of each element to moles. This can be done by dividing the given mass of each element by the molecular weight of each element.
After finding the moles of each element, you have to find the smallest whole number ratio of each element. The smallest whole number ratio can be found by dividing moles of each element by the lowest mole quantity (in this case, of oxygen). You are left with carbons, hydrogens, and oxygen. The empirical formula for this compound is .
To find the molecular formula of the compound you need to divide the molecular weight of the actual compound by the molecular weight of the empirical formula. The molecular weight of the empirical formula is:
Dividing the molecular weight of the actual compound (
) by the molecular weight of empirical formula gives:
This means that the empirical formula must be multiplied by three to get the molecular formula; therefore, the molecular formula is 
. Compared to the empirical formula, the molecular formula contains 
more carbon atoms and 
more oxygen atoms.
The first step in solving this question is to convert the mass of each element to moles. This can be done by dividing the given mass of each element by the molecular weight of each element.
After finding the moles of each element, you have to find the smallest whole number ratio of each element. The smallest whole number ratio can be found by dividing moles of each element by the lowest mole quantity (in this case,
To find the molecular formula of the compound you need to divide the molecular weight of the actual compound by the molecular weight of the empirical formula. The molecular weight of the empirical formula is:
Dividing the molecular weight of the actual compound (
This means that the empirical formula must be multiplied by three to get the molecular formula; therefore, the molecular formula is
← Didn't Know|Knew It →
A researcher performs an elemental analysis on a compound. He finds that the compound is made up of only carbon, hydrogen, and oxygen atoms. He isolates a pure sample of the compound and finds that this sample contains of carbon, of hydrogen, and of oxygen. The researcher wants to perform further analysis on this compound the next day. Before leaving the lab the researcher creates three stock solutions of varying concentrations of this compound: (solution A), (solution B), and (solution C). He stores these solutions overnight at a temperature of 
.
Molecular weight of this compound =
When calculating the empirical formula, if you used ratios of the number of atoms of each element instead of ratios of moles of each element, would you get a different answer?
A researcher performs an elemental analysis on a compound. He finds that the compound is made up of only carbon, hydrogen, and oxygen atoms. He isolates a pure sample of the compound and finds that this sample contains
Molecular weight of this compound =
When calculating the empirical formula, if you used ratios of the number of atoms of each element instead of ratios of moles of each element, would you get a different answer?
Tap to reveal answer
Remember that the empirical formula relies on the ratio of the moles of elements. To get the number of atoms, you would have to multiply the moles of each element by the Avogadro’s number (
). You would use this number for every element (Avogadro’s number doesn’t change for each element). This means that the ratio of the number of atoms will be the same as the ratio of the number of moles, and you will get the same empirical formula. There is a constant relationship between the number of moles and the number of atoms in a sample.
Remember that the empirical formula relies on the ratio of the moles of elements. To get the number of atoms, you would have to multiply the moles of each element by the Avogadro’s number (
← Didn't Know|Knew It →
A researcher performs an elemental analysis on a compound. He finds that the compound is made up of only carbon, hydrogen, and oxygen atoms. He isolates a pure sample of the compound and finds that this sample contains of carbon, of hydrogen, and of oxygen. The researcher wants to perform further analysis on this compound the next day. Before leaving the lab the researcher creates three stock solutions of varying concentrations of this compound: (solution A), (solution B), and (solution C). He stores these solutions overnight at a temperature of 
.
Molecular weight of this compound =
The researcher obtains a sample of 
of carbon-12. How many atoms of carbon-12 are present in this sample?
A researcher performs an elemental analysis on a compound. He finds that the compound is made up of only carbon, hydrogen, and oxygen atoms. He isolates a pure sample of the compound and finds that this sample contains
Molecular weight of this compound =
The researcher obtains a sample of
Tap to reveal answer
A mole is defined as the number of atoms present in 
of carbon-12. Obtaining a 
sample of carbon-12 will give you 
of carbon-12. You can also find the number of moles by multiplying the mass by the molecular weight of carbon:
Remember that a mole of any element contains 
atoms (Avogadro’s number). Since we have exactly one mole in the sample, there will be exactly 
atoms of carbon-12.
A mole is defined as the number of atoms present in
Remember that a mole of any element contains
← Didn't Know|Knew It →
Which of the following is both an empirical formula and a molecular formula?
Which of the following is both an empirical formula and a molecular formula?
Tap to reveal answer
An empirical formula is the simplest form of a molecular formula that still retains the ratio of the elements. If a formula can be divided by a whole number, it is a molecular formula and not an empirical formula. A molecular formula is the exact identity of a compound, showing the total number of atoms used to create the compound.
The only given answer that is not divisible by a whole number is 
, making it an empirical formula. It is also the molecular formula for both acetaldehyde and ethanol, depending on molecular geometry and orientation.
An empirical formula is the simplest form of a molecular formula that still retains the ratio of the elements. If a formula can be divided by a whole number, it is a molecular formula and not an empirical formula. A molecular formula is the exact identity of a compound, showing the total number of atoms used to create the compound.
The only given answer that is not divisible by a whole number is
← Didn't Know|Knew It →
Which of the following is a molecular formula but not an empirical formula?
Which of the following is a molecular formula but not an empirical formula?
Tap to reveal answer
An empirical formula is the simplest form of a molecular formula that still retains the ratio of the elements. If a formula can be divided by a whole number, it is a molecular formula and not an empirical formula. A molecular formula is the exact identity of a compound, showing the total number of atoms used to create the compound.
The only given answer that is fully divisible by a whole number is 
. This means it is not an empirical formula. Any given formula, however, will be a molecular formula, provided that the atoms are capable of forming the appropriate bonds. This is the molecular formula for glucose, which reduces to the empirical formula of 
. 
is the empirical formula for a generalized carbohydrate molecule.
An empirical formula is the simplest form of a molecular formula that still retains the ratio of the elements. If a formula can be divided by a whole number, it is a molecular formula and not an empirical formula. A molecular formula is the exact identity of a compound, showing the total number of atoms used to create the compound.
The only given answer that is fully divisible by a whole number is
← Didn't Know|Knew It →
Which of the following contains the greatest number of moles?
Which of the following contains the greatest number of moles?
Tap to reveal answer
Each answer choice is presented in grams. To convert to moles, we will need to divide each choice by the atomic mass of the presented element.
Two grams of hydrogen atoms will result in the greatest amount of moles.
Each answer choice is presented in grams. To convert to moles, we will need to divide each choice by the atomic mass of the presented element.
Two grams of hydrogen atoms will result in the greatest amount of moles.
← Didn't Know|Knew It →
Which of the following cannot be directly related to Avogadro's number by stoichiometry?
Which of the following cannot be directly related to Avogadro's number by stoichiometry?
Tap to reveal answer
Avogadro's number is used to convert between moles and atoms (or molecules).
This immediately eliminates two answer choices, since moles and molecules in a sample are both contained in the constant. Atoms in a sample of diatomic gas is also easily related to Avogadro's number, as each molecule in the sample will contain exactly two atoms. Avogadro's number can be used to determine the number of moles, molecules, or atoms in a sample of diatomic gas.
Converting grams in a sample to moles allows us to use Avogadro's number to further convert to molecules.
Partial pressure of a gas is directly related to mole fraction, but cannot be used to determine the moles of gas unless the total moles in the sample is known. Partial pressure represents a relationship between the sample and its particular environment, whereas constants govern conversion between moles, grams, atoms, and molecules. Since partial pressure is not directly related to these terms by a constant, Avogadro's number cannot be applied to partial pressure to determine any useful data.
Avogadro's number is used to convert between moles and atoms (or molecules).
This immediately eliminates two answer choices, since moles and molecules in a sample are both contained in the constant. Atoms in a sample of diatomic gas is also easily related to Avogadro's number, as each molecule in the sample will contain exactly two atoms. Avogadro's number can be used to determine the number of moles, molecules, or atoms in a sample of diatomic gas.
Converting grams in a sample to moles allows us to use Avogadro's number to further convert to molecules.
Partial pressure of a gas is directly related to mole fraction, but cannot be used to determine the moles of gas unless the total moles in the sample is known. Partial pressure represents a relationship between the sample and its particular environment, whereas constants govern conversion between moles, grams, atoms, and molecules. Since partial pressure is not directly related to these terms by a constant, Avogadro's number cannot be applied to partial pressure to determine any useful data.
← Didn't Know|Knew It →
Consider the following molecular formulas:
*The IUPAC name for DEET is N,N-diethyl-meta-toluamide
DEET has a density of 
. How many nitrogen atoms are found in one liter of DEET?
Consider the following molecular formulas:
*The IUPAC name for DEET is N,N-diethyl-meta-toluamide
DEET has a density of
Tap to reveal answer
To solve, we will need to find the mass of one liter of DEET and use the mass percentage of nitrogen to find the mass of nitrogen represented. Then, the atomic mass of nitrogen can be used to convert this to moles, and Avogadro's number can be used to convert to atoms.
First, find the mass of DEET in a one-liter sample:
Find the mass of nitrogen in 998 grams of DEET by finding the percentage of nitrogen by mass:
Use this mass percentage and atomic mass to find the moles of nitrogen in the one-liter sample.
Use Avogadro's number to find the number of atoms in this sample.
An alternative method would be to convert the grams of DEET to moles, and then from moles to molecules. There is one nitrogen atom per molecule of DEET, so this would method also get you the same answer.
To solve, we will need to find the mass of one liter of DEET and use the mass percentage of nitrogen to find the mass of nitrogen represented. Then, the atomic mass of nitrogen can be used to convert this to moles, and Avogadro's number can be used to convert to atoms.
First, find the mass of DEET in a one-liter sample:
Find the mass of nitrogen in 998 grams of DEET by finding the percentage of nitrogen by mass:
Use this mass percentage and atomic mass to find the moles of nitrogen in the one-liter sample.
Use Avogadro's number to find the number of atoms in this sample.
An alternative method would be to convert the grams of DEET to moles, and then from moles to molecules. There is one nitrogen atom per molecule of DEET, so this would method also get you the same answer.
← Didn't Know|Knew It →
A compound is found to have a molar mass of 
and is composed of 
carbon, 
hydrogen, and 
oxygen. What are the empirical and molecular formulas for the compound, respectively?
A compound is found to have a molar mass of
Tap to reveal answer
To find the empirical formula, we must first find the mole ratios by using molar masses for each element:
Rounding these numbers, we get five moles of carbon, ten moles of hydrogen, and two moles of oxygen, making the formula 
. The formula cannot be simplified by any common denominator, and thus represents the final empirical formula.
We know the molecular mass, given in the question. To find the molecular formula, we need to find the ratio of the mass of the empirical formula to the molecular mass.
The mass of the empirical formula is equal to the molecular mass, meaning that the empirical and molecular formulas are the same.
To find the empirical formula, we must first find the mole ratios by using molar masses for each element:
Rounding these numbers, we get five moles of carbon, ten moles of hydrogen, and two moles of oxygen, making the formula
We know the molecular mass, given in the question. To find the molecular formula, we need to find the ratio of the mass of the empirical formula to the molecular mass.
The mass of the empirical formula is equal to the molecular mass, meaning that the empirical and molecular formulas are the same.
← Didn't Know|Knew It →
Which of the following samples contains a larger mass of hydrogen?
Which of the following samples contains a larger mass of hydrogen?
Tap to reveal answer
Start by calculating the percentages of hydrogen in each compound by using molar mass ratios.
Next, take the percentages of the given sample masses to determine the total mass of hydrogen in each.
We see that there is a larger mass of hydrogen in the hydrogen cyanide sample.
Start by calculating the percentages of hydrogen in each compound by using molar mass ratios.
Next, take the percentages of the given sample masses to determine the total mass of hydrogen in each.
We see that there is a larger mass of hydrogen in the hydrogen cyanide sample.
← Didn't Know|Knew It →
Which of the following samples contains 
atoms?
Which of the following samples contains
Tap to reveal answer
The number of atoms in a sample is dependent on the molar quantity, NOT the mass of the sample. Avogadro's number shows that there are 
atoms in a mole of any element. Knowing this, we can find out how many moles of the element are represented by the given amount of atoms.
By dividing the mass of the samples by the molar mass of each respective element, we can find which sample has this molar quantity.
Sodium: 
Lithium: 
Potassium: 
As a result, a five-gram sample of sodium has 
.
The number of atoms in a sample is dependent on the molar quantity, NOT the mass of the sample. Avogadro's number shows that there are
By dividing the mass of the samples by the molar mass of each respective element, we can find which sample has this molar quantity.
Sodium:
Lithium:
Potassium:
As a result, a five-gram sample of sodium has
← Didn't Know|Knew It →
Calculate the mass percent of sulfur in sulfuric acid 
.
Calculate the mass percent of sulfur in sulfuric acid
Tap to reveal answer
To calculate the mass percent, calculate the the individual masses of each element. Then divide the mass of sulfur by the total mass of the molecule. Since there is only one sulfur atom in sulfuric acid, the mass of sulfur in one atom is 
.
To calculate the mass percent, calculate the the individual masses of each element. Then divide the mass of sulfur by the total mass of the molecule. Since there is only one sulfur atom in sulfuric acid, the mass of sulfur in one atom is
← Didn't Know|Knew It →
Compounds can be distinguished from each other by using their molecular weights. The molecular weight of a compound depends on the individual atomic weights of the elements and the amount of each element present in the compound. Consider hexane for example. Hexane has a molecular formula of 
. This means that it has 6 carbon atoms and 14 hydrogen atoms. To calculate the molecular weight of hexane, we can simply look up the molecular weight of carbon and hydrogen from the periodic table, multiply each molecular weight by the number of atoms (6 for carbon and 14 for hydrogen), and sum the two numbers. The molecular weight of an element is always given in 
. One mole is the defined as the number of atoms in twelve grams of carbon-12.
A researcher is trying to determine the molecular formula of a hydrocarbon molecule. He measures the molecular weight to be 
. He also observes that the molecule has one 
bond. What is the ratio of the number of carbon to hydrogen atoms in this molecule?
Compounds can be distinguished from each other by using their molecular weights. The molecular weight of a compound depends on the individual atomic weights of the elements and the amount of each element present in the compound. Consider hexane for example. Hexane has a molecular formula of
A researcher is trying to determine the molecular formula of a hydrocarbon molecule. He measures the molecular weight to be
Tap to reveal answer
The empirical formula for hydrocarbon is 
, where 
is the number of carbons. This is only true if the hydrocarbon has no 
bonds or ring structures. The question states that there is one 
bond; therefore, the hydrocarbon will lose two hydrogen atoms (
). Note that for every 
bond and every ring the hydrocarbon is associated with the loss of two hydrogen atoms. If we calculate the molecular weight of hydrocarbons with different 
values (
) we will find that the nine-carbon hydrocarbon (with 
bond), nonene, has a molecular weight of 
. The molecular formula for nonene is 
; therefore, the ratio of carbons to hydrogens is 9:18 or 1:2.
You can also calculate the ratio by simply looking at the empirical formula of this molecule (
). There will be twice as many hydrogen atoms as carbon atoms; therefore, ratio of carbon to hydrogen will be 1:2.
The empirical formula for hydrocarbon is
You can also calculate the ratio by simply looking at the empirical formula of this molecule (
← Didn't Know|Knew It →
Compounds can be distinguished from each other by using their molecular weights. The molecular weight of a compound depends on the individual atomic weights of the elements and the amount of each element present in the compound. Consider hexane for example. Hexane has a molecular formula of 
. This means that it has 6 carbon atoms and 14 hydrogen atoms. To calculate the molecular weight of hexane, we can simply look up the molecular weight of carbon and hydrogen from the periodic table, multiply each molecular weight by the number of atoms (6 for carbon and 14 for hydrogen), and sum the two numbers. The molecular weight of an element is always given in . One mole is the defined as the number of atoms in twelve grams of carbon-12.
How many atoms of oxygen are found in 1g of oxygen gas?
Compounds can be distinguished from each other by using their molecular weights. The molecular weight of a compound depends on the individual atomic weights of the elements and the amount of each element present in the compound. Consider hexane for example. Hexane has a molecular formula of
How many atoms of oxygen are found in 1g of oxygen gas?
Tap to reveal answer
To solve this question, we need to first convert grams to moles, then moles to atoms. The molecular weight (MW) of oxygen gas, 
is
The amount of moles in 1g of oxygen gas is
There are 
atoms in 
(this is called the Avogadro’s number); therefore, the number of atoms in 
of 
is
To solve this question, we need to first convert grams to moles, then moles to atoms. The molecular weight (MW) of oxygen gas,
The amount of moles in 1g of oxygen gas is
There are
← Didn't Know|Knew It →
Given the unbalanced equation above, how many moles of hydrocholoric acid would be required to produce four moles of potassium chloride?
Given the unbalanced equation above, how many moles of hydrocholoric acid would be required to produce four moles of potassium chloride?
Tap to reveal answer
It is first necessary to balance the equation.
So, sixteen moles of hydrochloric acid (HCl) would produce two moles of potassium chloride (KCl). Multiplying this ratio times two, thirty-two moles of HCl would produce four moles of KCl.
It is first necessary to balance the equation.
So, sixteen moles of hydrochloric acid (HCl) would produce two moles of potassium chloride (KCl). Multiplying this ratio times two, thirty-two moles of HCl would produce four moles of KCl.
← Didn't Know|Knew It →
Given the unbalanced equation below, how many grams of carbon dioxide will be produced from one mole of glucose and three moles of oxygen?
Given the unbalanced equation below, how many grams of carbon dioxide will be produced from one mole of glucose and three moles of oxygen?
Tap to reveal answer
The first step to solve will be to balance the chemical reaction:
We see that we see that for every one mole of glucose used, six moles of carbon dioxide will be made. Similarly, for every six moles of oxygen used, six moles of carbon dioxide will be formed. For the reaction to carry out to completion, however, there must exist six moles of oxygen for every one mole of glucose. In the problem's circumstances, one of these compounds becomes the limiting reactant, in this case it is oxygen.
We only have three moles of oxygen, but we would need six to react all the given glucose, making oxygen the limiting reagent. We need to find the carbon dioxide produced from the limited amount of oxygen present. Use the molar ratio between oxygen and carbon dioxide and the molar mass of carbon dioxide to solve.
The first step to solve will be to balance the chemical reaction:
We see that we see that for every one mole of glucose used, six moles of carbon dioxide will be made. Similarly, for every six moles of oxygen used, six moles of carbon dioxide will be formed. For the reaction to carry out to completion, however, there must exist six moles of oxygen for every one mole of glucose. In the problem's circumstances, one of these compounds becomes the limiting reactant, in this case it is oxygen.
We only have three moles of oxygen, but we would need six to react all the given glucose, making oxygen the limiting reagent. We need to find the carbon dioxide produced from the limited amount of oxygen present. Use the molar ratio between oxygen and carbon dioxide and the molar mass of carbon dioxide to solve.
← Didn't Know|Knew It →
Which represents the correct balanced equation for the reaction between silver (I) nitrate and magnesium hydroxide?
Which represents the correct balanced equation for the reaction between silver (I) nitrate and magnesium hydroxide?
Tap to reveal answer
Silver (I) nitrate is AgNO3. Recognizing this allows us to eliminate two answer choices, which incorrectly substitute nitrogen (N) for nitrate (NO3) or balance the molecular charges incorrectly. Of the two remaining choices, only one is balanced correctly.
Silver (I) nitrate is AgNO3. Recognizing this allows us to eliminate two answer choices, which incorrectly substitute nitrogen (N) for nitrate (NO3) or balance the molecular charges incorrectly. Of the two remaining choices, only one is balanced correctly.
← Didn't Know|Knew It →
5.6g of manganese reacts with 650mL of 6.0M hydrochloric acid to form manganese (V) chloride and hydrogen gas. Along with the products, a large amount of heat is evolved.
What is the limiting reagent, and how much of the excess reagent will remain after the reaction?
5.6g of manganese reacts with 650mL of 6.0M hydrochloric acid to form manganese (V) chloride and hydrogen gas. Along with the products, a large amount of heat is evolved.
What is the limiting reagent, and how much of the excess reagent will remain after the reaction?
Tap to reveal answer
Find the volume of hydrochloric acid (HCl) needed to react completely with 5.6g of manganese (Mn).
Since we only need 85mL of acid to react with 5.6g manganese, we have an excess of 565mL hydrochloric acid, and manganese is the limiting reagent.
Find the volume of hydrochloric acid (HCl) needed to react completely with 5.6g of manganese (Mn).
Since we only need 85mL of acid to react with 5.6g manganese, we have an excess of 565mL hydrochloric acid, and manganese is the limiting reagent.
← Didn't Know|Knew It →