Convert Grams to Moles

  • Grams to Moles

    Here we explain how grams are converted to moles. The conversion from moles to grams can be found here.  This area of ​​chemistry is called stoichiometry .

    You will need a periodic table and a calculator.

    First, identifying the elements that make up the compound. 
     
    • Example: the compound NaHCO 3  consists of four elements: sodium (Na), hydrogen (H), carbon (C) and oxygen (O).

     Then determine the number of atoms each element contributes to the compound.

    Example: H 2 O has two hydrogen and one oxygen atoms. If an index follows a bracket in a compound, each element in the bracket is multiplied by the index. For example, (NH 4 ) 2 S consists of two nitrogen atoms, one hydrogen atom and one sulfur atom. 

    Record the atomic weight of each element. A periodic table is the easiest way to determine the atomic weight of an element. Once you've found the element on a periodic table, the atomic weight is usually listed below the element symbol. For example, the atomic weight of oxygen is 15.99.

    Calculate Molecular Mass: The molecular mass of a substance is calculated by multiplying the number of atoms of each element by its respective atomic weight.

    To convert grams to moles, you need to know the molecular mass of the compound.

    Multiply the number of atoms of each element by its atomic weight.
    Add the total weights of all the elements in the compound together. Here you will find a periodic table to read the values.

    Example:

    • Let's say you have 2g of water, or H2O , and you want to know how much that is in moles. The molecular mass of H 2 O is 18g/mol. Divide 2 by 18 and get 0.1111 mol H 2 O. In the periodic table under H you will find the weight 1.0080 for hydrogen (top right in the box) and the weight 15.999 for oxygen (O). That's two times 1.0080 plus one time 15.999. Around 18 u or ame. Here you can find out more about the details of the atomic weight (u, or ame).

    First step

    Second stepMolInGram 2

    ResultMolInGram 3


    Another example:

    (NH 4 ) 2 S has the molecular mass of (2 x 14.01) + (8 x 1.01) + (1 x 32.07) = 68.17 g/mol.

    Molecular mass was previously also referred to as molecular weight.

    The number of moles in a compound can be calculated by dividing the number of grams of the compound by the molecular mass of the compound.

    • The formula looks like this: moles = grams of the compound : molecular mass of the compound.

    Once you have set up the formula, you can insert the calculations into the appropriate place in the formula. An easy way to check that everything is in the right place is to look at the units. You should be able to reduce all units so that only moles remain.

    Divide the number of grams by the molecular mass. The result is the number of moles in your element or compound. 

    Context: 

    ID: 545

  • Moles to Grams

    Here we explain how to convert moles to grams. The conversion from grams to moles can be found here.   This area of ​​chemistry is called stoichiometry .

    The mass in grams of a mole of a substance (that is, the mass in grams per mole) is called the molar mass of that substance. 

    The molar mass (in g/mol) of a substance is numerically always equal to the formula weight of the substance (in ame = atom mass unit or also called u = unit). The atomic mass can be found at the top right of every periodic table under atomic weight .

    The substance NaCl has e.g. B. a formula weight of 58.5 ame and a molar mass of 58.5 g/mol. The table below contains further examples of calculations using the mole unit.

    The entries for N and N 2  in the table make it clear that it is important to precisely name the chemical form of a substance when specifying an amount of substance in moles. Suppose it is stated that 1 mol of nitrogen is produced in a certain reaction. You might conclude that this means 1 mol of nitrogen atoms (14.0 g). However, unless otherwise stated, this probably means 1 mol of nitrogen molecules N2 (  28.0 g), because N2 is  the common chemical form of the element. To avoid such misunderstandings, the chemical form of the substance should be explicitly stated. By specifying the chemical formula N 2 , such misunderstandings are avoided.

    Substance name
    formula
    Formula weight
    in name
    Molar mass
    in (g/mol)
    Number & type of particles present in a mole
    Atomic nitrogen  N 14.0 14.0
    6.022 * 10 23  N atoms
    Molecular nitrogen  N2 _ 28.0 28.0
    6.022 * 10 23  N 2 molecules
    2 * (6.022 * 10 23)  N atoms
    Silver  Ag 107.9 107.9
    6.022 * 10 23  Ag atoms
    Silver ions  Ag + 107.9 107.9 (1 6.022 * 10 23 Ag + ions
    Barium chloride  BaCl2 _ 208.2 208.2
    6.022 * 10 23  BaCl 2 units
    6.022 * 10 23  Ba 2+  ions
    2 * (6.022*1023) Cl –  ions

     

    1) Remember that the mass of the electron can be neglected and therefore ions and atoms have essentially the same mass.

    Example:

    What is the mass in grams of 1,000 mol of glucose/sugar, C6 H12 O6  ?

     

    Solution:

    First: analysis. The chemical formula is given and we are supposed to calculate the molar mass from it.

    Procedure: The molar mass of a substance can be calculated by adding the atomic weights of the atomic components together.

    Glucose has a formula weight of 180.0 ame. One mole of this substance has a mass of 180.0 g, so the substance C 6 H 12 O 6  has a molar mass of 180.0 g/mol.

    Verification: The order of magnitude of our answer seems plausible and g/mol is the correct unit for specifying molar mass.

     6 C – Atoms = 6 (12.0 ame) = 72.0 ame
    12 H – Atoms = 12 (1.0 ame) = 12.0 ame
     6 O – atoms = 6 (16.0 ame) = 96.0 ame
    --------------------------------------
                                 180.0 ame or 180.0 u written
    tl;dr: forget about the decimal places in atomic weights - as long as it's about fertilizer.
     
    In order to be complete, one more detail needs to be explained. The information shown here assumes an ideal atomic weight, which cannot be found in the periodic table - with a few exceptions. If you look at the atomic weight of hydrogen, it should be exactly 1.0 u (or 1.0 ame). However, 1.0080 is given.
     
    This is where reality gets in the way. There is almost no element in nature that occurs without isotopes. The atoms in the periodic table are "sorted" according to the number of protons. But the number of neutrons can vary. For magnesium, for example, only about 78.6% contains 12 neutrons in any sample (i.e. no matter where you find magnesium on Earth). 10.1% have 13 neutrons and 11.3% of them have 14 protons. This is how you get an atomic weight of magnesium of 24.327 u. It works out like this:
     
    786 24 Mg isotopes with a mass of 24 u provide a mass of 18864 u.
    101  25 Mg isotopes with a mass of 25 u provide a mass of 2525 u.
    113  26 Mg isotopes with a mass of 25 u provide a mass of 2938 u.
    The total gives the weight of 1000 Mg atoms: 24,327 u. So statistically one Mg atom weighs 24.327 u.
     
    If you put together fertilizer according to your own formulas, this inaccuracy should only come into play for very (very) large quantities. This last paragraph only serves to remind you of the chemistry lessons you may have already forgotten at school and to clear up the confusion about the crooked numbers. 
    Context: 
    ID: 544

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