Introduction to Stoichiometry

Stoichiometry is the branch of chemistry that deals with elements, compounds, and the ratio of reactants and products in chemical reactions

• True

• False

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Reaction stoichiometry is based on chemical equations and

• a. the law of conservation of mass.

• b. the law of conservation of moles

• c. the law of conservation of molecules

• d. Avogadro’s law

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The number of significant figures in an answer to a mole city or stoichiometry problem is most often determined by:

• a. the number of significant figures in the coefficients used to balance the equation.

• b. the number of decimal places in the molar masses of substances on the periodic table.

• c. the number of significant figures of any measured quantities in the problem.

• d. the number of significant figures in Avogadro's number.

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The chemical equation P4O10 + 6H2O -> 4H3PO4 can be interpreted correctly as

• a. 1 molecule of P4O10 + 6 molecules of H2O form 4 molecules of H3PO4.

• b. 1 mol of P4O10 + 6 mol of H2O reacts to form 4 mol of H3PO4.

• c. 1 g of P4O10 + 6 g of H2O produces 4 g of H3PO4.

• d. Both (a) and (b)

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What is the ratio of moles of NaNO3 to CdS in the following chemical equation?

Na2S + Cd(NO3)2 -> 2NaNO3 + CdS

• 1:1

• 1:2

• 2:1

• 3:1

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NGSS.HS-PS1-7

In stoichiometry, molar mass is used to

• a. determine the mole ratio.

• b. balance a chemical equation.

• c. convert the amount in moles of one substance to an amount in moles of another substance.

• d. relate the mass of a substance to the amount in moles of that substance.

Molar mass can be used to relate

• a. mass of reactant to moles of reactant.

• b. moles of product to mass of product.

• c. mass of product to moles of product.

• d. All of the above

In the chemical reaction described by the equation

4Fe(s) + 3O2(g) --> 2Fe2O3(s),

the mole ratio of iron(III) oxide to iron is

• 1:1

• 1:2

• 2:3

• 4:1

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NGSS.HS-PS1-7

How many steps would it take to know if how many grams of Copper (II) Sulfate reacts with 2.00g of Iron? Assume you have the balanced equation

• a. 0 steps - You already know the answer, which is 2.00 grams

• b. 2 steps - You need to convert 2.00g Iron to moles, compare mole ratios and that is your answer

• c. 1 step - just convert 2.00g of Iron to moles and that is your answer

• d. 3 steps - Convert 2.00g Iron to Moles, then compare mole ratios, then convert to grams of copper sulfate

In the chemical equation wA + xB --> yC + zD, if you know the

number of moles of A that react, you can determine

• a. the number of moles of each reactant and product.

• b. the number of moles of B only.

• c. the total number of moles of C and D only.

• d. the total number of moles of A and B only.

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NGSS.HS-PS1-7