Help with Molecular Weight and Molar Mass - AP Chemistry
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Consider the following reaction:
How much ammonia will be created if 
of nitrogen gas is used in the reaction?
Consider the following reaction:
How much ammonia will be created if
Since we are given the mass of nitrogen gas that will be used, we will need to convert the amount into moles. We can then compare the molar ratios in the balanced reaction, and multiply the moles of ammonia by its molar mass. Using dimensional analysis, we can use a calculation that will allow us to end with "grams of ammonia" as the solved unit.
Since we are given the mass of nitrogen gas that will be used, we will need to convert the amount into moles. We can then compare the molar ratios in the balanced reaction, and multiply the moles of ammonia by its molar mass. Using dimensional analysis, we can use a calculation that will allow us to end with "grams of ammonia" as the solved unit.
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What is the percent composition by mass of oxygen in a molecule of glucose?
What is the percent composition by mass of oxygen in a molecule of glucose?
The formula for glucose is 
.
First, we must find the molecular weight of the entire molecule of glucose. We do this individually for each element. Using oxygen as an example, we multiply the atomic mass (16) by the number of atoms per glucose molecule:
We do similar calculations for carbon and hydrogen to find our total molecular weight for glucose.
Sum these values to find the molecular weight.
Next, to find percent composition by mass for oxygen, we are being asked to find how much of one molecule of glucose's weight comes from oxygen. To do this we divide the mass of oxygen by the molecular weight:
Thus 53.3% of the mass of glucose comes from oxygen alone.
The formula for glucose is
First, we must find the molecular weight of the entire molecule of glucose. We do this individually for each element. Using oxygen as an example, we multiply the atomic mass (16) by the number of atoms per glucose molecule:
We do similar calculations for carbon and hydrogen to find our total molecular weight for glucose.
Sum these values to find the molecular weight.
Next, to find percent composition by mass for oxygen, we are being asked to find how much of one molecule of glucose's weight comes from oxygen. To do this we divide the mass of oxygen by the molecular weight:
Thus 53.3% of the mass of glucose comes from oxygen alone.
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What is the mass of 25 iron atoms?
What is the mass of 25 iron atoms?
First, convert the number of atoms to moles using Avogadro's number:
Next, convert moles of iron to grams of iron using the molar mass:
First, convert the number of atoms to moles using Avogadro's number:
Next, convert moles of iron to grams of iron using the molar mass:
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How many moles are in a 
sample of 
?
How many moles are in a
To find the number of moles in a sample, use the periodic table to find the molar mass. Since the atomic weights of 
and 
are 
and 
, respectively, add the two atomic masses to determine the molar mass of 
Next, use dimensional analysis to find the number of moles in the given mass of the sample.
To find the number of moles in a sample, use the periodic table to find the molar mass. Since the atomic weights of
Next, use dimensional analysis to find the number of moles in the given mass of the sample.
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How many grams of 
are in 5.61mol of 
?
How many grams of
Use the periodic table to compute the molecular mass of 
.
Next, use dimensional analysis to convert grams to moles.
Use the correct number of significant figures.
Use the periodic table to compute the molecular mass of
Next, use dimensional analysis to convert grams to moles.
Use the correct number of significant figures.
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A silicon microchip weighs 7.2mg. How many atoms of silicon are in the microchip?
A silicon microchip weighs 7.2mg. How many atoms of silicon are in the microchip?
First convert the 7.2mg of silicon into grams:
Then convert grams of silicon into moles of silicon:
Finally, convert moles of silicon into atoms using Avogadro's number:
Since 7.2mg of silicon is much less than 1 mole (which we know weighs 28.09g) our answer makes sense as it is much less than Avogadro's number.
First convert the 7.2mg of silicon into grams:
Then convert grams of silicon into moles of silicon:
Finally, convert moles of silicon into atoms using Avogadro's number:
Since 7.2mg of silicon is much less than 1 mole (which we know weighs 28.09g) our answer makes sense as it is much less than Avogadro's number.
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Blood contains various dissolved ions including calcium 
, which is involved in many biological processes (like muscle contraction). One liter of blood from an unknown animal was shown to contain 
of 
. Calculate the mass of calcium atoms in one liter of blood.
Blood contains various dissolved ions including calcium
The answer is not present, but 
equates to 
.
Use Avogadro's number to convert from atoms to moles:
Convert from moles of 
to grams of 
:
The answer is not present, but
Use Avogadro's number to convert from atoms to moles:
Convert from moles of
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How many neutrons does calcium-42 have?
How many neutrons does calcium-42 have?
The 42 in calcium-42 represents the mass number of calcium. The mass number equals the sum of the number of protons and the number of neutrons. Using the periodic table, the number of protons in calcium can be determined using the atomic number. The atomic number of calcium is 20.
Using all this information the number of neutrons can be determined by subtracting the number of protons from the atomic mass number. The number of neutrons is 22.
Atomic Mass Number = Protons + Neutrons
Atomic Mass Number - Protons = Neutrons
The 42 in calcium-42 represents the mass number of calcium. The mass number equals the sum of the number of protons and the number of neutrons. Using the periodic table, the number of protons in calcium can be determined using the atomic number. The atomic number of calcium is 20.
Using all this information the number of neutrons can be determined by subtracting the number of protons from the atomic mass number. The number of neutrons is 22.
Atomic Mass Number = Protons + Neutrons
Atomic Mass Number - Protons = Neutrons
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An atom contains 
and 
. What is the mass number of this atom?
An atom contains
The mass number is equal to the number of protons plus the number of neutrons in an atom.
Protons + Neutrons = Mass Number
The mass number is equal to the number of protons plus the number of neutrons in an atom.
Protons + Neutrons = Mass Number
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What is the atomic number of calcium?
What is the atomic number of calcium?
The atomic number is equal to the number of protons in an atom and can be determined using the periodic table. The atomic number is located on the top left of the box containing the desired chemical symbol. The chemical symbol for calcium is Ca and the atomic number is 20.
The atomic number is equal to the number of protons in an atom and can be determined using the periodic table. The atomic number is located on the top left of the box containing the desired chemical symbol. The chemical symbol for calcium is Ca and the atomic number is 20.
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What is the chemical symbol for an atom with 
and 
?
What is the chemical symbol for an atom with
To determine the chemical symbol of an atom we can use the atomic number because no two elements have the same atomic number. The atomic number is equal to the number of protons, and is usually located on the top left of the element's box in the periodic table. This atom has 8 protons, therefore the atomic number is 8. Using this information it can be determined that the chemical symbol for an atom with 8 protons is O, oxygen.
To determine the chemical symbol of an atom we can use the atomic number because no two elements have the same atomic number. The atomic number is equal to the number of protons, and is usually located on the top left of the element's box in the periodic table. This atom has 8 protons, therefore the atomic number is 8. Using this information it can be determined that the chemical symbol for an atom with 8 protons is O, oxygen.
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How many protons does potassium-40 have?
How many protons does potassium-40 have?
The number of protons is equal to the atomic number of an element. The atomic number of an element can usually be found on the top right of the element box in the periodic table. The chemical symbol for potassium is K
. Using all this information the atomic number of 
is 19, therefore the number of protons in potassium-40 is 19.
The number of protons is equal to the atomic number of an element. The atomic number of an element can usually be found on the top right of the element box in the periodic table. The chemical symbol for potassium is K
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Elements in the periodic table are arranged according to their __________.
Elements in the periodic table are arranged according to their __________.
The elements are arranged based on their atomic number. The atomic number can usually be found on the top left of each element's box. The atomic number increased from left to right as you move across the periodic table.
The elements are arranged based on their atomic number. The atomic number can usually be found on the top left of each element's box. The atomic number increased from left to right as you move across the periodic table.
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What is the mass in grams of 
of magnesium?
What is the mass in grams of
To determine the mass in grams of 
of magnesium, we need to know the molecular mass of magnesium, which can be found on the periodic table.
The molecular mass of magnesium is 
. Now we have all the information we need to convert moles to grams:
In the above conversion, the moles cancel to leave the answer in grams.
To determine the mass in grams of
The molecular mass of magnesium is
In the above conversion, the moles cancel to leave the answer in grams.
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How many moles of potassium are there in 
of potassium?
How many moles of potassium are there in
To determine the number of moles in 
of potassium, we need to convert grams to moles. To convert grams to moles we need to determine the atomic mass of potassium using the periodic table. The atomic mass of potassium is 
.
Using this information we can convert grams to moles:
To determine the number of moles in
Using this information we can convert grams to moles:
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How many moles of tungsten are in 
atoms?
How many moles of tungsten are in
To convert atoms to moles we need to know that there are 
atoms in one mole.
To convert atoms to moles we need to know that there are
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How many atoms are in 
of 
?
How many atoms are in
To determine the how many atoms are in 
of aluminum, we need to also know that there are 
atoms in one mole.
To determine the how many atoms are in
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What is the mass in grams of 
of 
?
What is the mass in grams of
To determine the mass in grams of 
of nickel, we first need to convert atoms to moles. To do this we need to know that 
. Then we will convert moles to grams using the atomic mass of nickel, which can be found on the periodic table. The atomic mass of 
is 
.
Now we have all of the information we need to perform the conversion:
To determine the mass in grams of
Now we have all of the information we need to perform the conversion:
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How many atoms of sulfur are in 
of 
?
How many atoms of sulfur are in
The conversion of grams to atoms is a two-step process. First, we need to convert grams to moles using the molecular mass of sulfur. The molecular mass of sulfur can be found on the periodic table and is equal to 
Then we will convert moles to atoms using our knowledge that 
. Using all this information we will perform the following conversion:
The conversion of grams to atoms is a two-step process. First, we need to convert grams to moles using the molecular mass of sulfur. The molecular mass of sulfur can be found on the periodic table and is equal to
Then we will convert moles to atoms using our knowledge that
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Consider the following reaction:
How much ammonia will be created if of nitrogen gas is used in the reaction?
Consider the following reaction:
How much ammonia will be created if
Since we are given the mass of nitrogen gas that will be used, we will need to convert the amount into moles. We can then compare the molar ratios in the balanced reaction, and multiply the moles of ammonia by its molar mass. Using dimensional analysis, we can use a calculation that will allow us to end with "grams of ammonia" as the solved unit.
Since we are given the mass of nitrogen gas that will be used, we will need to convert the amount into moles. We can then compare the molar ratios in the balanced reaction, and multiply the moles of ammonia by its molar mass. Using dimensional analysis, we can use a calculation that will allow us to end with "grams of ammonia" as the solved unit.
Compare your answer with the correct one above