Question 1

The _____ is defined as the number equal to the number of carbon atoms in exactly 12 grams of pure ¹²C.

Accepted Answer

The definition given in the question is that of a mole. It is a unit used in chemistry to represent a specific number of particles, specifically 6.022 x 10^23 particles (also known as Avogadro's number).

Question 2

A white salt sample is analyzed and found to be made of potassium, oxygen, and carbon. It contains 56.58% of potassium and 34.73% of oxygen. The salt has a molar mass of 138.205 g. Compute the salt's empirical and molecular formulas.

Accepted Answer

The empirical formula is KC₂O₂, and the molecular formula is K₂C₂O₂.

Question 3

​Nicotine is a stimulant drug that contains carbon, hydrogen, and nitrogen. The mass percent of carbon, hydrogen, and nitrogen in nicotine is 74.03%, 8.698%, and 17.267%, respectively. If the molar mass of nicotine is 162.23 g, determine its molecular formula.

Accepted Answer

The empirical formula based on mass percentages is C₅H₇N. The empirical formula mass is approximately 81.12 g/mol. Dividing the molar mass of nicotine (162.23 g/mol) by the empirical formula mass gives a factor of 2, indicating the molecular formula is C₁₀H₁₄N₂.

Question 4

A sample of a compound containing hydrogen, carbon, and sulfur is reacted with oxygen. The carbon content in the carbon dioxide obtained is 41.34% and the hydrogen content in the water obtained is 3.47%. Determine the empirical formula of the compound.​

Accepted Answer

Assume we have 100g of the compound. Then, we have 41.34g of carbon and 3.47g of hydrogen. The remaining mass is sulfur. 
Let's calculate the number of moles of each element: 
- Carbon: 41.34g / 12.01 g/mol = 3.44 mol
- Hydrogen: 3.47g / 1.01 g/mol = 3.44 mol
- Sulfur: (100g - 41.34g - 3.47g) / 32.07 g/mol = 1.56 mol
Divide each value by the smallest number of moles (1.56 mol) to get the empirical formula:
- Carbon: 3.44 mol / 1.56 mol = 2.205 ≈ 2
- Hydrogen: 3.44 mol / 1.56 mol = 2.205 ≈ 2
- Sulfur: 1.56 mol / 1.56 mol = 1
The empirical formula is therefore CS2H2S. The only choice that matches this formula is B.

Question 5

​A sample of dysprosium (atomic mass 162.5 u) contains 8 atoms. Determine the mass of the sample.

Accepted Answer

The mass of one atom of dysprosium is 162.5 u. For 8 atoms, the total mass is $8 \times 162.5 = 1300$ u. Since 1 u is equal to $1.660539 \times 10^{-24}$ g, the mass in grams is $1300 \times 1.660539 \times 10^{-24} = 2.1587 \times 10^{-21}$ g, which is closest to option A.

Quiz 3: Stoichiometry

The _____ is defined as the number equal to the number of carbon atoms in exactly 12 grams of pure 12C.​

A white salt sample is analyzed and found to be made of potassium, oxygen, and carbon. It contains 56.58% of potassium and 34.73% of oxygen. The salt has a molar mass of 138.205 g. Compute the salt's empirical and molecular formulas.

​Nicotine is a stimulant drug that contains carbon, hydrogen, and nitrogen. The mass percent of carbon, hydrogen, and nitrogen in nicotine is 74.03%, 8.698%, and 17.267%, respectively. If the molar mass of nicotine is 162.23 g, determine its molecular formula.

A sample of a compound containing hydrogen, carbon, and sulfur is reacted with oxygen. The carbon content in the carbon dioxide obtained is 41.34% and the hydrogen content in the water obtained is 3.47%. Determine the empirical formula of the compound.​

​A sample of dysprosium (atomic mass 162.5 u) contains 8 atoms. Determine the mass of the sample.

The _____ is defined as the number equal to the number of carbon atoms in exactly 12 grams of pure ¹²C.

Nicotine is a stimulant drug that contains carbon, hydrogen, and nitrogen. The mass percent of carbon, hydrogen, and nitrogen in nicotine is 74.03%, 8.698%, and 17.267%, respectively. If the molar mass of nicotine is 162.23 g, determine its molecular formula.

A sample of a compound containing hydrogen, carbon, and sulfur is reacted with oxygen. The carbon content in the carbon dioxide obtained is 41.34% and the hydrogen content in the water obtained is 3.47%. Determine the empirical formula of the compound.

A sample of dysprosium (atomic mass 162.5 u) contains 8 atoms. Determine the mass of the sample.