Q1. Balance the following equation. How many carbon atoms are on the reactant side?

C5H10O2 + O2 ⟶ CO2 + H2O

Background

Topic: Balancing Chemical Equations & Counting Atoms

This question tests your ability to interpret a chemical equation and count the number of specific atoms (carbon) on the reactant side before balancing.

Key Terms and Concepts:

• Reactant side: The left side of the chemical equation.

• Subscript: The small number after an element symbol in a formula, indicating the number of atoms of that element in one molecule.

Step-by-Step Guidance

1. Identify the chemical formula for each reactant. Here, focus on C5H10O2.

2. Look at the subscript for carbon (C) in C5H10O2. This tells you how many carbon atoms are in one molecule.

3. Check if there is a coefficient in front of C5H10O2 (in the unbalanced equation, there is not).

4. Multiply the coefficient (if any) by the subscript to get the total number of carbon atoms on the reactant side.

Try solving on your own before revealing the answer!

Q2. Balance the reaction between aluminum hydroxide and sulfuric acid to form aluminum sulfate and water. How many total oxygen atoms are on the products side of the balanced equation?

Background

Topic: Balancing Chemical Equations & Atom Counting

This question tests your ability to balance a chemical reaction and count the total number of oxygen atoms in the products.

Key Terms and Concepts:

• Balancing equations: Making sure the number of each type of atom is the same on both sides.

• Product side: The right side of the equation.

• Aluminum hydroxide: Al(OH)3

• Sulfuric acid: H2SO4

• Aluminum sulfate: Al2(SO4)3

• Water: H2O

Step-by-Step Guidance

1. Write the unbalanced equation: Al(OH)3 + H2SO4 ⟶ Al2(SO4)3 + H2O.

2. Balance the equation by adjusting coefficients so that the number of each atom is equal on both sides.

3. Once balanced, count the number of oxygen atoms in each product molecule (Al2(SO4)3 and H2O).

4. Multiply the number of oxygen atoms in each molecule by its coefficient, then sum for all products.

Try solving on your own before revealing the answer!

Q3. Of the reactions below, which is not a combination reaction?

• a. C + O2 ⟶ CO2

• b. 2 Mg + O2 ⟶ 2 MgO

• c. 2 N2 + 3 H2 ⟶ 2 NH3

• d. 2 Al + 6 HCl ⟶ 3 H2 + 2 AlCl3

Background

Topic: Types of Chemical Reactions

This question tests your ability to identify combination (synthesis) reactions, where two or more reactants form a single product.

Key Terms:

• Combination (synthesis) reaction: Two or more substances combine to form one product.

• Other types: Decomposition, single replacement, double replacement, combustion.

Step-by-Step Guidance

1. Review each reaction and count the number of reactants and products.

2. For a combination reaction, there should be two or more reactants and only one product.

3. Identify which reaction does not fit this pattern.

Try solving on your own before revealing the answer!

Q4. Which of the following equations is a decomposition reaction?

• a. 2 CH4 + 4 O2 ⟶ 2 CO2 + 4 H2O

• b. 2 Mg + O2 ⟶ 2 MgO

• c. NH4Cl ⟶ NH3 + HCl

• d. Zn + 2 HCl ⟶ H2 + ZnCl2

Background

Topic: Types of Chemical Reactions

This question tests your ability to recognize a decomposition reaction, where a single compound breaks down into two or more simpler substances.

Key Terms:

• Decomposition reaction: A single reactant breaks down into two or more products.

Step-by-Step Guidance

1. Look for the reaction with only one reactant on the left side.

2. Check that the single reactant forms two or more products.

3. Compare each option to this pattern.

Try solving on your own before revealing the answer!

Q5. What is the molar mass of calcium acetate?

Background

Topic: Molar Mass Calculation

This question tests your ability to calculate the molar mass of a compound from its chemical formula.

Key Terms and Formula:

• Molar mass: The mass (in grams) of one mole of a substance.

• Calcium acetate: Ca(C2H3O2)2

• Atomic masses: Ca = 40.08 g/mol, C = 12.01 g/mol, H = 1.008 g/mol, O = 16.00 g/mol

Step-by-Step Guidance

1. Write the formula: Ca(C2H3O2)2.

2. Count the number of each atom: 1 Ca, 4 C, 6 H, 4 O.

3. Multiply the number of each atom by its atomic mass.

4. Add up all the masses to get the total molar mass.

Try solving on your own before revealing the answer!

Q6. What is the molar mass of ammonium sulfate?

Background

Topic: Molar Mass Calculation

This question tests your ability to determine the molar mass of a compound from its formula.

Key Terms and Formula:

• Ammonium sulfate: (NH4)2SO4

• Atomic masses: N = 14.01 g/mol, H = 1.008 g/mol, S = 32.07 g/mol, O = 16.00 g/mol

Step-by-Step Guidance

1. Write the formula: (NH4)2SO4.

2. Count the number of each atom: 2 N, 8 H, 1 S, 4 O.

3. Multiply the number of each atom by its atomic mass.

4. Add up all the masses to get the total molar mass.

Try solving on your own before revealing the answer!

Q7. When the following equation is balanced, the coefficients are ________?

C8H18 + O2 ⟶ CO2 + H2O

Background

Topic: Balancing Chemical Equations

This question tests your ability to balance a combustion reaction and identify the correct set of coefficients.

Key Terms:

• Coefficient: The number in front of a chemical formula indicating the number of molecules or moles.

• Combustion reaction: A hydrocarbon reacts with O2 to form CO2 and H2O.

Step-by-Step Guidance

1. Write the unbalanced equation: C8H18 + O2 ⟶ CO2 + H2O.

2. Balance carbon atoms first by adjusting the coefficient for CO2.

3. Balance hydrogen atoms by adjusting the coefficient for H2O.

4. Balance oxygen atoms last by adjusting the coefficient for O2.

Try solving on your own before revealing the answer!

Q8. How many hydrogen atoms are in 24.68 grams of NH3?

Background

Topic: Mole Concept and Avogadro's Number

This question tests your ability to convert grams to moles, then to molecules, and finally to atoms.

Key Terms and Formulas:

• Molar mass of NH3: 17.03 g/mol

• Avogadro's number: particles/mol

• Each NH3 molecule contains 3 H atoms.

Step-by-Step Guidance

1. Calculate moles of NH3:

2. Find the number of NH3 molecules:

3. Multiply by 3 to get the number of hydrogen atoms:

Try solving on your own before revealing the answer!

Q9. What is the empirical formula of a compound with 3.407 moles of carbon, 4.54 moles of hydrogen, and 3.406 moles of oxygen?

Background

Topic: Empirical Formula Determination

This question tests your ability to determine the simplest whole-number ratio of atoms in a compound.

Key Terms and Formula:

• Empirical formula: The simplest whole-number ratio of atoms in a compound.

Step-by-Step Guidance

1. List the moles of each element: C = 3.407, H = 4.54, O = 3.406.

2. Divide each by the smallest number of moles to get the ratio.

3. Round to the nearest whole number (if necessary, multiply all ratios by a common factor to get whole numbers).

Try solving on your own before revealing the answer!

Q10. What is the empirical formula of a compound that is 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen by mass?

Background

Topic: Empirical Formula from Percent Composition

This question tests your ability to convert percent composition to an empirical formula.

Key Terms and Formula:

• Empirical formula: Simplest whole-number ratio of atoms.

• Assume 100 g sample: 40.0 g C, 6.7 g H, 53.3 g O.

• Convert grams to moles:

Step-by-Step Guidance

1. Convert each percent to grams (assume 100 g sample).

2. Convert grams to moles for each element.

3. Divide each by the smallest number of moles to get the ratio.

4. Adjust to whole numbers if needed.

Try solving on your own before revealing the answer!

Q11. If the molar mass of the compound described by the empirical formula CH3N is 116 g/mol, what is the molecular formula?

Background

Topic: Molecular Formula Determination

This question tests your ability to use the empirical formula and molar mass to find the molecular formula.

Key Terms and Formula:

• Empirical formula mass: Sum of atomic masses in CH3N.

• Molecular formula: (Empirical formula)n, where n = (molar mass)/(empirical formula mass).

Step-by-Step Guidance

1. Calculate the empirical formula mass for CH3N.

2. Divide the given molar mass by the empirical formula mass to find n.

3. Multiply each subscript in the empirical formula by n to get the molecular formula.

Try solving on your own before revealing the answer!

Q12. In the following reaction, 3.5 moles of O3 are reacted with 4.0 moles of NaI and 1.5 moles of H2O. What is the limiting reactant?

O3 + 2 NaI + H2O ⟶ O2 + I2 + 2 NaOH

Background

Topic: Limiting Reactant

This question tests your ability to identify the limiting reactant in a chemical reaction given the starting amounts of each reactant.

Key Terms and Formula:

• Limiting reactant: The reactant that is completely consumed first, limiting the amount of product formed.

• Use mole ratios from the balanced equation to compare how much product each reactant could make.

Step-by-Step Guidance

1. Write the balanced equation and note the mole ratios for each reactant.

2. Calculate how many "reactions" each reactant can support based on the coefficients.

3. The reactant that supports the fewest complete reactions is the limiting reactant.

Try solving on your own before revealing the answer!

Q13. Using the information provided for the reaction in question 12, how many grams of I2 is formed in the reaction?

Background

Topic: Stoichiometry – Mass of Product from Limiting Reactant

This question tests your ability to use the limiting reactant to calculate the mass of product formed.

Key Terms and Formula:

• Stoichiometry: Calculating amounts of reactants and products using balanced equations.

• Molar mass of I2: 253.8 g/mol

Step-by-Step Guidance

1. Identify the limiting reactant from Q12.

2. Use the mole ratio between the limiting reactant and I2 from the balanced equation.

3. Calculate the moles of I2 produced.

4. Convert moles of I2 to grams using its molar mass.

Try solving on your own before revealing the answer!

Q14. 5.0 moles of lithium hydroxide and 4.0 moles of carbon dioxide are reacted to form lithium carbonate and water. What mass of the excess reactant is left over once the reaction is complete?

Background

Topic: Limiting Reactant and Excess Calculation

This question tests your ability to determine how much of the excess reactant remains after a reaction goes to completion.

Key Terms and Formula:

• Limiting reactant: Used up first.

• Excess reactant: Left over after the reaction.

• Balanced equation: 2 LiOH + CO2 ⟶ Li2CO3 + H2O

Step-by-Step Guidance

1. Write the balanced equation and identify the mole ratios.

2. Determine which reactant is limiting by comparing the mole ratios to the amounts given.

3. Calculate how much of the excess reactant is used up.

4. Subtract the amount used from the initial amount to find the leftover mass.

Try solving on your own before revealing the answer!

Q15. In the following reaction, how many grams of water can be formed from 4.00 grams of NH3 and 5.0 grams of O2?

4 NH3 + 5 O2 ⟶ 4 NO + 6 H2O

Background

Topic: Limiting Reactant and Mass-to-Mass Stoichiometry

This question tests your ability to determine the limiting reactant and calculate the mass of product formed.

Key Terms and Formula:

• Limiting reactant: Determines the maximum amount of product.

• Molar mass of NH3: 17.03 g/mol

• Molar mass of O2: 32.00 g/mol

• Molar mass of H2O: 18.02 g/mol

Step-by-Step Guidance

1. Convert grams of NH3 and O2 to moles.

2. Use the balanced equation to determine the limiting reactant.

3. Use the limiting reactant to calculate moles of H2O produced.

4. Convert moles of H2O to grams.

Try solving on your own before revealing the answer!

Q16. How many moles of product can be formed in the combination reaction to form iron(III) chloride from 3.5 moles of iron and 2.5 moles of chlorine?

Background

Topic: Limiting Reactant and Stoichiometry

This question tests your ability to use mole ratios to determine the amount of product formed from given reactant amounts.

Key Terms and Formula:

• Balanced equation: 2 Fe + 3 Cl2 ⟶ 2 FeCl3

• Limiting reactant: The reactant that runs out first.

Step-by-Step Guidance

1. Write the balanced equation and note the mole ratios.

2. Calculate how many moles of FeCl3 can be formed from each reactant.

3. The smaller value determines the maximum moles of product.

Try solving on your own before revealing the answer!

Q17. How many grams of lithium nitride can be formed when 3.5 grams of lithium and 2.5 grams of nitrogen are reacted in a combination reaction?

Background

Topic: Limiting Reactant and Mass-to-Mass Stoichiometry

This question tests your ability to determine the mass of product formed from given masses of reactants.

Key Terms and Formula:

• Balanced equation: 6 Li + N2 ⟶ 2 Li3N

• Molar mass of Li: 6.94 g/mol

• Molar mass of N2: 28.02 g/mol

• Molar mass of Li3N: 34.83 g/mol

Step-by-Step Guidance

1. Convert grams of Li and N2 to moles.

2. Use the balanced equation to determine the limiting reactant.

3. Calculate moles of Li3N formed from the limiting reactant.

4. Convert moles of Li3N to grams.

Try solving on your own before revealing the answer!

Q18. For the reaction in question 17, if the actual yield is 3.52 g, what is the percent yield?

Background

Topic: Percent Yield Calculation

This question tests your ability to calculate percent yield from actual and theoretical yields.

Key Terms and Formula:

• Percent yield:

Step-by-Step Guidance

1. Use the theoretical yield from Q17.

2. Plug the actual yield and theoretical yield into the percent yield formula.

3. Calculate the percent yield.

Try solving on your own before revealing the answer!

Q19. How many grams of K2O are needed to react with excess water to form 4.50 grams of potassium hydroxide? Assume a yield of 100%.

Background

Topic: Stoichiometry – Reactant Mass Calculation

This question tests your ability to use stoichiometry to determine the mass of a reactant needed to produce a given mass of product.

Key Terms and Formula:

• Balanced equation: K2O + H2O ⟶ 2 KOH

• Molar mass of K2O: 94.20 g/mol

• Molar mass of KOH: 56.11 g/mol

Step-by-Step Guidance

1. Convert grams of KOH to moles.

2. Use the balanced equation to find moles of K2O needed.

3. Convert moles of K2O to grams.

Try solving on your own before revealing the answer!

Q20. To an empty container, 4.50 moles of H2(g) and 8.50 moles of N2(g) are added and they begin to react and form NH3(g). At some point in time, there are 3.5 moles of H2(g) remaining. At this point, what are the total moles of gas in the container?

Background

Topic: Stoichiometry and Conservation of Mass (Moles)

This question tests your ability to track the changes in moles of reactants and products as a reaction proceeds.

Key Terms and Formula:

• Balanced equation: N2 + 3 H2 ⟶ 2 NH3

• Track moles: Subtract moles reacted, add moles of product formed.

Step-by-Step Guidance

1. Calculate how many moles of H2 have reacted (initial - remaining).

2. Use the stoichiometric ratio to find moles of N2 reacted and NH3 formed.

3. Calculate the moles of each gas present at this point.

4. Add up the moles of all gases to get the total.

Try solving on your own before revealing the answer!