Chemistry Concepts: Moles and Limiting Reactants

How many formula units are in a given number of moles?

• 6.022 x 10^23 formula units per mole

• 3.011 x 10^23 formula units per mole

• 1.204 x 10^24 formula units per mole

• None of the above

How to convert mass (grams) to moles?

• By dividing the mass by the molar mass

• By multiplying the mass by the molar mass

• By adding the mass to the molar mass

• By subtracting the molar mass from the mass

How to find the amount of product produced in a reaction given the reactants? For a chemical reaction like: Fe2+(aq) + 2 SCN−(aq) → Fe(SCN)2(s), this equation tells you that: 1 mole of Fe2+ reacts with 2 moles of SCN− to form 1 mole of Fe(SCN)2.

• By using stoichiometry to calculate the moles of product from the moles of reactants.

• By measuring the temperature change in the reaction.

• By observing the color change in the reaction.

• By calculating the pH of the solution.

Avogadro's number is used to:

• determine the number of atoms or molecules in a mole of a substance

• measure the volume of a gas at standard temperature and pressure

• calculate the energy of a photon

• find the pH of a solution

The mass of one mole of a substance is called:

• Molar mass

• Atomic mass

• Molecular weight

• Avogadro's number

Which of the following is used to convert between grams and moles?

• Avogadro's number

• Molar Mass

• Stoichiometry

• Limiting Reactant

Complete, Balance, and Identify the Equations: a. Molecular Equation - The molecular equation shows the complete compounds in their undissolved state or as they appear in solution without breaking them into ions. Example formula: 2 NaCl (aq)+Pb(NO3)2(aq)→PbCl2(s)+2 NaNO3(aq)2NaCl (aq)+Pb(NO3)2(aq)→PbCl2(s)+2NaNO3(aq). Explanation: In this molecular equation, we write the reactants and products as whole compounds. (aq) means the substance is dissolved in water, and (s) means it is a solid (precipitate).

• What is the state of NaCl in the molecular equation?

• What is the state of PbCl2 in the molecular equation?

• What is the state of NaNO3 in the molecular equation?

• What is the state of Pb(NO3)2 in the molecular equation?

Complete, Balance, and Identify the Equations: b. Total Ionic Equation - The total ionic equation shows all the ions that are present in the solution, where soluble compounds are broken into their respective ions. Example: 2 Li+(aq)+SO42−(aq)+Sr2+(aq)+2 Cl−(aq)→2 Li+(aq)+2 Cl−(aq)+SrSO4(s)2Li+(aq)+SO42−(aq)+Sr2+(aq)+2Cl−(aq)→2Li+(aq)+2Cl−(aq)+SrSO4(s). Explanation: (aq) is for aqueous, meaning the ions are dissolved in the solution. We show all the ions involved in the reaction, not just the compounds.

• The total ionic equation shows all the ions present in the solution.

• The total ionic equation shows only the compounds involved in the reaction.

• The total ionic equation does not include aqueous ions.

• The total ionic equation is the same as the molecular equation.

Balance the Reaction and Identify Precipitate: To balance the equation, we need to make sure that the number of atoms of each element is the same on both sides. This will give us a balanced equation. For the equation:

• Balance the Reaction and Identify Precipitate

• Identify the Catalyst and Balance the Reaction

• Determine the Limiting Reactant and Balance the Reaction

• Calculate the Molar Mass and Balance the Reaction

The importance of balancing atoms in the reaction: Fe2(SO4)3(aq) + 3 Ba(NO3)2(aq) → 2 Fe(NO3)3(aq) + 3 BaSO4(s) is to:

• ensure the conservation of mass.

• increase the reaction rate.

• produce more products.

• change the state of reactants.