In chemistry, the mole is a standard unit of measurement that refers to the individual elements that make up a substance. Often the quantities of the compounds are expressed in grams, therefore needing to be converted into moles. You'll get a clearer picture of the number of molecules you work with if you make this conversion instead of using weight, which can vary from one molecule to another. While the conversion process is simple, it is important to perform some basic steps. Using this guide you will be able to learn how to convert grams to moles.
Steps
Part 1 of 2: Calculate the Molecular Mass
Step 1. Get the tools you need to find the solution to a chemistry problem
Having everything you need available allows you to simplify the process of finding the solution to the problem. Here's what you need:
- Pencil and sheet of paper - the calculations to be carried out will be easier if you have the possibility to put them on paper; furthermore, for your solution to be considered valid, you will need to show all the steps taken to get there;
- A periodic table - used to obtain the atomic weight of the basic elements that form chemical compounds;
- A calculator - is needed to greatly simplify calculations involving complex numbers.
Step 2. Identify the chemical elements that characterize the compound to be expressed in moles
The first step in calculating the molecular mass is to identify all the elements that are part of the chemical compound in question. This step is simple, since the initials of each element consist of one or two letters.
- If an element's abbreviation consists of two letters, the first will be uppercase, the second lowercase. For example, "Mg" is the abbreviation for magnesium.
- The chemical compound identified by the formula "NaHCO3"has 4 elements inside: Sodium (Na), Hydrogen (H), Carbon (C) and Oxygen (O).
Step 3. Determine the number of atoms each element provides to the final compound
In order to calculate the molecular mass, you need to know the number of atoms of each element in the compound. This information is written as a subscript of each element.
- For example, the compound "H2O "has two atoms of hydrogen and one of oxygen.
- If the formula of the compound is enclosed in brackets and has a subscript number, it means that each element present in the compound must be multiplied by the number indicated in the subscript of the formula. For example, the compound "(NH4)2S "has two" N "atoms, eight" H "atoms and one" S "atom.
Step 4. Note the atomic weight of each element
To do this in the simplest way possible, we need to refer to the periodic table of chemical elements. Once the element in question has been identified in the table, the atomic weight is normally indicated under its chemical symbol.
- The atomic weight, or mass, of an element is expressed in atomic mass units (amu, from the English "atomic mass unit").
- For example, the mass of an oxygen atom is 15.99.
Step 5. Calculate the molecular mass
To do this, it is necessary to multiply the number of atoms of each element present in the compound by the respective atomic weight. Knowing the molecular mass is necessary in order to convert grams into moles.
- Multiply the number of atoms of each element in the compound by its respective atomic weight.
- At the end, add together the atomic weight of the individual elements present in the compound.
- For example, the compound "(NH4)2S "has a molecular mass of (2 * 14.01) + (8 * 1.01) + (1 * 32.07) = 68.17 g / mol.
- Molecular mass is also called molar mass.
Part 2 of 2: Converting Grams to Moles
Step 1. Set the formula to perform the conversion
The number of moles of a given chemical compound can be calculated by dividing the number of grams by the molecular mass.
The formula is as follows: moles = grams of chemical compound / molecular mass of the chemical compound
Step 2. Enter the values into the formula
After setting the formula correctly, the next step is to replace the variables with real values. A simple way to check that everything is correct is to look at the units of measure. Simplifying the units of measurement present in the formula should remain only the moles.
Step 3. Solve the equation
Use the calculator to divide grams by molecular mass. The result will be the number of moles of your chemical element or compound.
For example, let's assume we have 2 grams of (NH4)2S and want to convert them to moles. The molecular mass of the compound (NH4)2S is 68.17 g / mol. Dividing 2 by 68.17 yields 0.0293 moles of (NH4)2S.
Advice
- In your solution to the problem always include the name of the element or compound in question.
- If you are asked to show work done for your assigned assignment or chemistry exam, be sure to highlight the final result by highlighting it with a circle or box.
