Reviewing materials for stoichiometry unit

How many atoms are in N₂?

What is the total number of atoms in Pb(C₂H₃O₂)₂?

How many atoms of carbon are in Pb(C₂H₃O₂)₂?

What is the gram-formula mass (gfm) for N₂?

• 14 g/mol

• 28 g/mol

• 32 g/mol

• 44 g/mol

Answer explanation

The gram-formula mass (gfm) for N2 is 28 g/mol because nitrogen (N) has an atomic mass of 14 g/mol, and there are two nitrogen atoms in N2, making it 28 g/mol.

What is the gram-formula mass (gfm) for Pb(C₂H₃O₂)₂?

• 325.2 g/mol

• 278.1 g/mol

• 303.2 g/mol

• 367.3 g/mol

Answer explanation

The gram-formula mass (gfm) for Pb(C2H3O2)2 is calculated by adding the atomic masses of each element: Pb(207.2) + 2(C2H3O2)(118.1) = 325.2 g/mol.

94.3 g is how many moles of NaCl?

• 1.61 moles

• 2.00 moles

• 1.00 mole

• 0.80 moles

Answer explanation

To find the moles of NaCl, divide the given mass by the molar mass of NaCl (58.44 g/mol). 94.3 g / 58.44 g/mol = 1.61 moles, so the correct answer is 1.61 moles.

6.5 moles of Mg(NO₃)₂ is how many grams?

• 148.3 grams

• 162.5 grams

• 505.3 grams

• 813.7 grams

Answer explanation

The molar mass of Mg(NO3)2 is 148.3 g/mol. Therefore, 6.5 moles of Mg(NO3)2 is 6.5 * 148.3 = 505.3 grams.

What is the percent by mass of magnesium in Mg(NO₃)₂?

• 10%

• 20%

• 24.1%

• 28.6%

Answer explanation

To calculate the percent by mass of magnesium in Mg(NO3)2, find the molar mass of Mg(NO3)2 and the molar mass of Mg. Then, divide the molar mass of Mg by the molar mass of Mg(NO3)2 and multiply by 100 to get 24.1%.

How many moles are there in 4.8 x 10^24 atoms of carbon (C)?

• 8 moles

• 4 moles

• 12 moles

• 20 moles

Answer explanation

To find the number of moles, divide the number of atoms by Avogadro's number (6.022 x 10^23). 4.8 x 10^24 / 6.022 x 10^23 = 8 moles.

Which of the following best defines empirical formula, molecular formula, and hydrate?

• Empirical formula shows the simplest ratio of elements, molecular formula shows the actual number of atoms, and hydrate is a compound with water molecules.

• Empirical formula and molecular formula are the same, and hydrate does not contain water.

• Molecular formula shows the simplest ratio of elements, empirical formula shows compounds without water, and hydrate is a type of molecular formula.

• Hydrate shows the simplest ratio of elements, empirical formula is a type of hydrate, and molecular formula cannot be determined.

Answer explanation

The correct choice is: Empirical formula shows the simplest ratio of elements, molecular formula shows the actual number of atoms, and hydrate is a compound with water molecules.