1.
What is the molar mass of water (H2O)?
Correct Answer
A. 18 g/mol
Explanation
The molar mass of water (H₂O) is 18 grams per mole (g/mol). To find this, you add the atomic masses of the elements in a water molecule. Hydrogen (H) has an atomic mass of approximately 1 g/mol, and there are two hydrogen atoms in water, so that's 2 g/mol. Oxygen (O) has an atomic mass of about 16 g/mol. Adding these together (2 + 16) gives you 18 g/mol. This means that one mole of water molecules weighs 18 grams. The molar mass is important for converting between moles and grams in chemistry calculations.
2.
How many grams are in 2 moles of carbon dioxide (CO2)?
Correct Answer
C. 88 g
Explanation
To find out how many grams are in 2 moles of carbon dioxide (CO₂), you need to know the molar mass of CO₂. The molar mass of CO₂ is 44 grams per mole (g/mol). This is because carbon (C) has a molar mass of 12 g/mol and oxygen (O) has a molar mass of 16 g/mol. Since there are two oxygen atoms, you multiply 16 by 2 to get 32 g/mol. Adding the carbon and oxygen masses together (12 + 32), you get 44 g/mol. For 2 moles, you multiply 44 g/mol by 2, which equals 88 grams.
3.
What is the mass in grams of 0.5 moles of sulfuric acid (H2SO4)?
Correct Answer
B. 49 g
Explanation
To find the mass in grams of 0.5 moles of sulfuric acid (H₂SO₄), you first need to determine the molar mass of H₂SO₄. Hydrogen (H) has a molar mass of 1 g/mol and there are 2 hydrogen atoms, so that's 2 g/mol. Sulfur (S) has a molar mass of 32 g/mol, and oxygen (O) has a molar mass of 16 g/mol with 4 oxygen atoms, so that's 64 g/mol (16 × 4). Adding these together (2 + 32 + 64), the molar mass of H₂SO₄ is 98 g/mol. For 0.5 moles, multiply 98 g/mol by 0.5, which equals 49 grams.
4.
How many moles are in 20 grams of NaCl?
Correct Answer
C. 0.342 mol
Explanation
To find out how many moles are in 20 grams of sodium chloride (NaCl), you need to know the molar mass of NaCl. Sodium (Na) has a molar mass of 23 grams per mole (g/mol) and chlorine (Cl) has a molar mass of 35.5 g/mol. Adding these together gives a molar mass of 58.5 g/mol for NaCl. To find the number of moles, you divide the mass by the molar mass. So, 20 grams divided by 58.5 g/mol equals approximately 0.342 moles. This means there are 0.342 moles in 20 grams of NaCl.
5.
What is the molar mass of ammonia (NH3)?
Correct Answer
D. 17 g/mol
Explanation
The molar mass of ammonia (NH₃) is 17 grams per mole (g/mol). To calculate this, you add the atomic masses of the elements in the ammonia molecule. Nitrogen (N) has an atomic mass of 14 g/mol, and hydrogen (H) has an atomic mass of 1 g/mol. Since there are three hydrogen atoms in ammonia, you multiply the atomic mass of hydrogen by 3 (1 × 3), which equals 3 g/mol. Adding the nitrogen and hydrogen masses together (14 + 3), you get 17 g/mol. This means one mole of ammonia weighs 17 grams.
6.
How many grams are in 1 mole of potassium permanganate (KMnO4)?
Correct Answer
D. 158.03
Explanation
To find the mass of 1 mole of potassium permanganate (KMnO₄), you need to calculate its molar mass. Potassium (K) has a molar mass of 39.1 g/mol, manganese (Mn) has a molar mass of 54.9 g/mol, and oxygen (O) has a molar mass of 16 g/mol. Since there are four oxygen atoms, you multiply 16 by 4 to get 64 g/mol. Adding these together (39.1 + 54.9 + 64), the total molar mass of KMnO₄ is 158.03 g/mol. Therefore, 1 mole of potassium permanganate weighs 158.03 grams.
7.
What is the mass in grams of 2.5 moles of methane (CH4)?
Correct Answer
C. 40 g
Explanation
To find the mass in grams of 2.5 moles of methane (CH₄), you need to know the molar mass of methane. Carbon (C) has a molar mass of 12 grams per mole (g/mol) and hydrogen (H) has a molar mass of 1 g/mol. Since there are four hydrogen atoms, you multiply the atomic mass of hydrogen by 4 (1 × 4), which equals 4 g/mol. Adding the carbon and hydrogen masses together (12 + 4), the molar mass of methane is 16 g/mol. For 2.5 moles, you multiply 16 g/mol by 2.5, which equals 40 grams.
8.
How many moles are in 75 grams of calcium carbonate (CaCO3)?
Correct Answer
B. 0.75 moles
Explanation
To find out how many moles are in 75 grams of calcium carbonate (CaCO₃), you need to know its molar mass. Calcium (Ca) has a molar mass of 40 grams per mole (g/mol), carbon (C) has a molar mass of 12 g/mol, and oxygen (O) has a molar mass of 16 g/mol. There are three oxygen atoms, so multiply 16 by 3 to get 48 g/mol. Adding these together (40 + 12 + 48), the molar mass of CaCO₃ is 100 g/mol. To find the number of moles, divide 75 grams by 100 g/mol, which equals 0.75 moles.
9.
What is the molar mass of sulfuric acid (H2SO4)?
Correct Answer
C. 98 g/mol
Explanation
The molar mass of sulfuric acid (H₂SO₄) is 98 grams per mole (g/mol). To calculate this, you add the atomic masses of each element in the molecule. Hydrogen (H) has an atomic mass of 1 g/mol, and there are two hydrogen atoms, so that’s 2 g/mol. Sulfur (S) has an atomic mass of 32 g/mol. Oxygen (O) has an atomic mass of 16 g/mol, and there are four oxygen atoms, so that’s 64 g/mol (16 × 4). Adding these together (2 + 32 + 64) gives a total molar mass of 98 g/mol for sulfuric acid.
10.
What is the molar mass of carbon dioxide (CO2)?
Correct Answer
A. 44 g/mol
Explanation
The molar mass of carbon dioxide (CO₂) is 44 grams per mole (g/mol). To calculate this, you add the atomic masses of the elements in the molecule. Carbon (C) has an atomic mass of 12 g/mol. Oxygen (O) has an atomic mass of 16 g/mol, and since there are two oxygen atoms, you multiply 16 by 2 to get 32 g/mol. Adding these together (12 + 32), the total molar mass of CO₂ is 44 g/mol. This means that one mole of carbon dioxide weighs 44 grams.