# Sample problems elemental chemistry

1. Question: What is the mass in grams of 1 mole of carbon (C¹²) atoms? Solution: The mass of 1 mole of any substance is equal to its molar mass. The molar mass of carbon is approximately 12.01 g/mol. So, the mass of 1 mole of carbon atoms is approximately 12.01 grams.

2. Question: How many moles are there in 56 grams of iron (Fe⁵⁶)? Solution: The molar mass of iron (Fe) is 55.85 g/mol. Therefore, 56 grams of iron is equal to 56 g / 55.85 g/mol = 1.0027 moles.
3. Question: What is the mass in grams of 2 moles of oxygen (O¹⁶) atoms? Solution: The molar mass of oxygen is approximately 16 g/mol. Therefore, the mass of 2 moles of oxygen atoms is 2 x 16 g/mol = 32 grams.
4. Question: How many moles are there in 24 grams of carbon (C¹²)? Solution: The molar mass of carbon is 12 g/mol. So, 24 grams of carbon equals 24 g / 12 g/mol = 2 moles.
5. Question: What is the mass in grams of 0.5 moles of hydrogen (H¹)? Solution: The molar mass of hydrogen is approximately 1 g/mol. Therefore, the mass of 0.5 moles of hydrogen atoms is 0.5 x 1 g/mol = 0.5 grams.
6. Question: How many atoms are in 3 moles of helium (He⁴)? Solution: One mole of any substance contains 6.022 x 10²³ entities (Avogadro’s number). So, 3 moles of helium contain 3 x 6.022 x 10²³ atoms = 1.8066 x 10²⁴ atoms.
7. Question: Calculate the number of atoms in 0.25 moles of neon (Ne²⁰)? Solution: There are 0.25 x 6.022 x 10²³ = 1.5055 x 10²³ atoms in 0.25 moles of neon.
8. Question: What is the molar mass of water (H₂O)? Solution: The molar mass of water is (2 x hydrogen) + oxygen = (2 x 1.01 g/mol) + 16.00 g/mol = 18.02 g/mol.
9. Question: How many grams are in 4 moles of nitrogen (N¹⁴) molecules (N₂)? Solution: The molar mass of nitrogen is 14 g/mol, so the molar mass of N₂ is 28 g/mol. Therefore, 4 moles of N₂ weigh 4 x 28 g/mol = 112 grams.
10. Question: How many moles are in 36 grams of water (H₂O)? Solution: The molar mass of water is 18.02 g/mol. So, 36 grams of water is 36 g / 18.02 g/mol = 2 moles.
11. Question: How many moles are there in 98 grams of sulfur (S³²)? Solution: The molar mass of sulfur is 32 g/mol. So, 98 grams of sulfur equals 98 g / 32 g/mol = 3.0625 moles.
12. Question: What is the mass of 3 moles of magnesium (Mg²⁴)? Solution: The molar mass of magnesium is 24 g/mol. Therefore, the mass of 3 moles of magnesium is 3 x 24 g/mol = 72 grams.
13. Question: How many atoms are in 1.5 moles of phosphorus (P³¹)? Solution: One mole contains 6.022 x 10²³ entities. So, 1.5 moles of phosphorus contain 1.5 x 6.022 x 10²³ atoms = 9.033 x 10²³ atoms.
14. Question: Calculate the number of moles in 40 grams of calcium (Ca⁴⁰). Solution: The molar mass of calcium is 40 g/mol. Therefore, 40 grams of calcium equals 40 g / 40 g/mol = 1 mole.
15. Question: How many grams are in 2.5 moles of potassium (K³⁹)? Solution: The molar mass of potassium is 39 g/mol. Therefore, the mass of 2.5 moles of potassium is 2.5 x 39 g/mol = 97.5 grams.
16. Question: What is the mass in grams of 5 moles of aluminum (Al²⁷)? Solution: The molar mass of aluminum is 27 g/mol. Therefore, the mass of 5 moles of aluminum is 5 x 27 g/mol = 135 grams.
17. Question: How many moles are in 160 grams of oxygen (O¹⁶) molecules (O₂)? Solution: The molar mass of O₂ is 32 g/mol. So, 160 grams of oxygen is 160 g / 32 g/mol = 5 moles.
18. Question: Calculate the number of atoms in 2 moles of silicon (Si²⁸). Solution: One mole contains 6.022 x 10²³ entities. So, 2 moles of silicon contain 2 x 6.022 x 10²³ atoms = 1.2044 x 10²⁴ atoms.
19. Question: How many moles are in 127 grams of iodine (I¹²⁷)? Solution: The molar mass of iodine is 127 g/mol. Therefore, 127 grams of iodine equals 127 g / 127 g/mol = 1 mole.
20. Question: What is the mass in grams of 0.75 moles of chlorine (Cl³⁵)? Solution: The molar mass of chlorine is 35.5 g/mol. Therefore, the mass of 0.75 moles of chlorine atoms is 0.75 x 35.5 g/mol = 26.625 grams.