![]() (ii) relationship between number of hydrogen atoms and number of water molecules:įrom the molecular formula we see that 1 molecule of water is made up of 2 atoms of hydrogen and 1 atom of oxygen. N(H 2O molecules) = number of water molecules N(H 2O molecules) = n(H 2O molecules) × N A (i) relationship between moles of water molecules and number of water molecules is: Step 4: What is the relationship between moles of water molecules and number of hydrogen atoms? ![]() Step 3: What is the relationship between moles of particles and number of particles? N(H 2O molecules) = moles of water molecules = 1.5 mol N(H atoms) = number of hydrogen atoms = ? Determine the number of hydrogen atoms in 1.5 moles of water, H 2O, molecules. Number of ammonia molecules = 2.1 × 10 24 molecules (Note: 2 significant figures are justified) Step 5: Substitute in the vales and solve for N: Step 4: Write the equation for the relationship between between moles of ammonia molecules and number of ammonia molecules: Step 3: What is the relationship between the moles of particles and the number of particles? N = amount of ammonia molecules in moles = 3.5 mol Step 2: What information (data) has been given in the question? N(ammonia) = number of ammonia molecules = ? Step 1: What is the question asking you to do?Ĭalculate the number of ammonia molecules. Question 1: Calculate the number of ammonia, NH 3, molecules in 3.5 moles of ammonia. Step 5: Substitute in the vales and solve for the unknownĬalculating the number of particles (N = n × N A).Step 4: Write the equation for the specific relationship you need to solve the problem.Step 3: What is the general relationship between the moles of particles and the number of particles?.Step 2: What information (data) has been given in the question?.Step 1: What is the question asking you to do?.The solutions to these problems are given as a set of 6 general steps to help structure your approach to problem solving: Worked Examples: Moles-Avogadro Number Calculations Moles of atoms of element Y = n(Y) = (N × b) ÷ N AĬonsider the following examples in which 1.927 × 10 24 molecules of a compound with the general formula X 2Y are present Moles of atoms of element X = n(X) = (N × a) ÷ N A Number of atoms of element Y = N(Y) = N × b Number of atoms of element X = N(X) = N × a The equation n = N ÷ N A can also be used to find the amount in moles of atoms or ions in a compound if you know both the molecular formula for the compound and the number of molecules of the compound that are present.įor N molecules of a compound with the general formula X aY b: If you know a substance contains 3.011 × 10 23 particles of the substance, then the moles of substance will be (3.011 × 10 23) ÷ (6.022 × 10 23) = 0.5 molģ.011 × 10 23 helium atoms = 0.5 mol of helium atomsģ.011 × 10 23 sodium ions = 0.5 mol of sodium ionsģ.011 × 10 23 water molecules = 0.5 mol of water molecules ![]() The table below gives the moles of each element present in the compound, and also shows us how to calculate the number of atoms of each element present: (n × b) × 6.022 × 10 23 atoms of element YĬonsider n moles of each of these compounds with the general formula XY 2. ![]() The mathematical equation, N = n × N A, can also be used to find the number of atoms of each element in a known amount (in moles) of a compound.įor a compound with the molecular formula X aY b: The mathematical equation, N = n × N A, can be used to find the number of atoms, ions or molecules in any amount (in moles) of atoms, ions or molecules: ![]()
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