BMST - Basic Math and Science Chemical Reactions and Stoichiometry Questions and Answers

Question 1

When the following chemical equation is balanced, what is the correct coefficient for sodium hydroxide (NaOH)?  ___ FeCl₃ + ___ NaOH → ___ Fe(OH)₃ + ___ NaCl

Accepted Answer

3

Answer

To balance the equation, we must have the same number of each type of atom on both sides. The unbalanced equation has 1 Fe, 3 Cl, 1 Na, 1 O, and 1 H on the left, and 1 Fe, 1 Cl, 1 Na, 3 O, and 3 H on the right. To balance the Cl atoms, a coefficient of 3 is needed for NaCl. To balance the Na atoms, a coefficient of 3 is then needed for NaOH. This also balances the O and H atoms. The final balanced equation is FeCl₃ + 3NaOH → Fe(OH)₃ + 3NaCl.

Question 2

A chemist observes a reaction where a single, complex compound breaks down into two or more simpler substances when heat is applied. Which of the following reaction types does this observation describe?

Accepted Answer

Decomposition

Answer

A decomposition reaction is a type of chemical reaction in which one compound breaks down into two or more simpler substances. The general form is AB → A + B. Synthesis is the opposite (A + B → AB), while single and double replacement reactions involve the exchange of elements between two or more compounds.

Question 3

What is the approximate molar mass of magnesium nitrate, Mg(NO₃)₂?

Accepted Answer

148.3 g/mol

Answer

To calculate the molar mass, sum the atomic masses of all atoms in the formula. Mg: 24.3 g/mol. N: 14.0 g/mol. O: 16.0 g/mol. The formula Mg(NO₃)₂ has 1 Mg, 2 N, and 6 O atoms. Molar Mass = (1 × 24.3) + (2 × 14.0) + (6 × 16.0) = 24.3 + 28.0 + 96.0 = 148.3 g/mol.

Question 4

In the complete combustion of propane (C₃H₈), the balanced equation is: C₃H₈ + 5O₂ → 3CO₂ + 4H₂O. If 44.1 g of propane is burned, how many grams of carbon dioxide (CO₂) are produced?

Accepted Answer

132.3 g

Answer

First, find the moles of propane (C₃H₈, molar mass ≈ 44.1 g/mol): 44.1 g / 44.1 g/mol = 1.0 mole C₃H₈. According to the balanced equation, the mole ratio of C₃H₈ to CO₂ is 1:3. So, 1.0 mole of C₃H₈ will produce 3.0 moles of CO₂. Finally, convert moles of CO₂ to grams (molar mass of CO₂ ≈ 44.0 g/mol): 3.0 moles × 44.0 g/mol = 132.0 g. The closest answer is 132.3 g.

Question 5

A technician is performing a reaction that requires 1 mole of reactant X for every 2 moles of reactant Y. The technician mixes 3 moles of X with 5 moles of Y. Which of the following statements is true?

Accepted Answer

Reactant Y is the limiting reactant, and some X will be left over.

Answer

To completely use 3 moles of X, you would need 3 moles X * (2 moles Y / 1 mole X) = 6 moles of Y. Since only 5 moles of Y are available, Y is the limiting reactant. To completely use 5 moles of Y, you would need 5 moles Y * (1 mole X / 2 moles Y) = 2.5 moles of X. Since 3 moles of X are available, there is an excess of X. Therefore, reactant Y is the limiting reactant and will be completely consumed, leaving some reactant X.

BMST - Basic Math and Science Test Practice Test

BMST - Basic Math and Science Test Practice Test

BMST - Basic Math and Science Chemical Reactions and Stoichiometry Questions and Answers