Mole Concept Examples and Solved Problems for 10th Grade

📚 Quick Study Guide

• ⚖️ The mole (mol) is the SI unit for the amount of a substance. It's defined as the amount of substance containing as many elementary entities (atoms, molecules, ions, etc.) as there are atoms in 12 grams of carbon-12.
• ⚗️ Avogadro's number ($N_A$) is approximately $6.022 \times 10^{23}$ entities per mole. This means 1 mole of anything contains $6.022 \times 10^{23}$ of those things.
• ⚸ Molar mass (M) is the mass of one mole of a substance, usually expressed in grams per mole (g/mol). It's numerically equal to the atomic or molecular weight of the substance.
• 🧪 Formula to calculate the number of moles (n): $n = \frac{m}{M}$, where 'm' is the mass of the substance and 'M' is the molar mass.
• 💡 Molar mass of a compound = sum of atomic masses of each element x number of atoms of that element present in the compound. For example, Molar mass of $H_2O$ = 2(1) + 1(16) = 18 g/mol

Practice Quiz

1. Question 1: How many moles are there in 48 grams of magnesium (Mg)? (Atomic mass of Mg = 24 g/mol)
   1. A) 0.5 moles
   2. B) 2 moles
   3. C) 1 mole
   4. D) 4 moles
2. Question 2: What is the molar mass of sodium chloride (NaCl)? (Atomic mass of Na = 23 g/mol, Cl = 35.5 g/mol)
   1. A) 58.5 g/mol
   2. B) 12.5 g/mol
   3. C) 71 g/mol
   4. D) 46 g/mol
3. Question 3: How many grams are there in 0.25 moles of calcium carbonate ($CaCO_3$)? (Molar mass of $CaCO_3$ = 100 g/mol)
   1. A) 25 g
   2. B) 400 g
   3. C) 100 g
   4. D) 0.25 g
4. Question 4: How many molecules are there in 1 mole of oxygen ($O_2$)?
   1. A) $3.011 \times 10^{23}$
   2. B) $6.022 \times 10^{23}$
   3. C) $12.044 \times 10^{23}$
   4. D) $1.0 \times 10^{23}$
5. Question 5: What is the mass of 2 moles of water ($H_2O$)? (Molar mass of $H_2O$ = 18 g/mol)
   1. A) 9 g
   2. B) 18 g
   3. C) 36 g
   4. D) 20 g
6. Question 6: How many moles are present in 11.5 g of sodium? (Atomic mass of Na = 23 g/mol)
   1. A) 1 mole
   2. B) 2 moles
   3. C) 0.5 moles
   4. D) 11.5 moles
7. Question 7: What is the molar mass of $CO_2$? (Atomic mass of C = 12 g/mol, O = 16 g/mol)
   1. A) 28 g/mol
   2. B) 32 g/mol
   3. C) 44 g/mol
   4. D) 16 g/mol