The mole is a standard unit of measurement in chemistry that takes into account the different elements in chemical compounds. Often times, the amount of a compound is given in grams and must be converted to moles. Although, the conversion is easy, there are some important steps to follow. Using this method, you can learn how to convert grams to moles.
Step
Part 1 of 2: Calculating Molecular Mass
Step 1. Gather the tools needed to solve the chemistry problem
Providing everything you need to make it easy to pick up will simplify the process of solving the assigned questions. You need the following:
- Pencil and paper. Calculations are easier to complete if you write them down. Be sure to write down all of your working steps to get the full score.
- Periodic table. You should be able to find the atomic weights of the elements using the periodic table.
- Calculator. Calculators are needed to simplify the calculation of complex numbers.
Step 2. Identify the elements in the compound that you must convert to moles
The first step in calculating the molecular mass is to identify the individual elements that make up the compound. It is easy to distinguish the elements because the abbreviation consists of only one or two letters.
- If a compound is abbreviated to two letters, the first letter will be written in uppercase or capital letters while the second letter will be written in lowercase. For example, Mg stands for Magnesium.
- NaHCO. compound3 has four elements in it: Sodium (Na), Hydrogen (H), Carbon (C), and Oxygen (O).
Step 3. Determine the number of atoms each element has in the compound
You must know the number of atoms of each element present to calculate the molecular mass. The number of atoms contained in each element will be written as a small number below which is next to the element.
- For example, H2O has two hydrogen atoms and one oxygen atom.
- If a compound has parentheses and is followed by a lowercase number, all elements in the parentheses are multiplied by the lowercase number. For example, (NH4)2S has two N atoms, eight H atoms, and one S atom.
Step 4. Write down the atomic weight of each element
The periodic table is the easiest way to find the atomic weight of an element. Once you know the location of the element in the table, the atomic weight is usually found under the element's symbol.
- The weight or mass of an atom or element is expressed in atomic mass units (amu).
- For example, the molecular weight of oxygen is 15.99.
Step 5. Calculate the molecular mass
The molecular mass of a substance is calculated by counting the number of atoms of each element multiplied by the atomic weight of that element. Knowing the molecular mass is necessary to convert grams to moles.
- Multiply the number of atoms of each element in the compound by the atomic weight of that element.
- Add up the total weight of each element in the compound.
- For example, (NH4)2S has a molecular weight (2 x 14.01) + (8 x 1.01) + (1 x 32.07) = 68.17 g/mol.
- The molecular mass is also known as the molar mass.
Part 2 of 2: Converting Grams To Mol
Step 1. Write down the conversion formula
The number of moles you have 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 compound/molar mass of compound
Step 2. Plug your numbers into the formula
After you have written the formula correctly, the next step is simply to enter your calculations into the correct part of the formula. An easy way to check if you've written everything in the correct place is to look at the units. Crossing out all the units will only leave moles.
Step 3. Solve the equation
Using a calculator, divide the gram by the molar mass. The result is the number of moles in your element or compound.
For example, imagine you have 2 g of water, or H2O, and you want to convert it to moles. Molecular mass of H2O is 18g/mol. Divide 2 by 18, and you have 0.1111 moles of H2O.
Tips
- Always include the name of the element or compound in your answers.
- If you are asked to show your work on your chemistry assignment or test, be sure to write your answer clearly by circling it or drawing a box around your answer.
