Q: If you are given the volume and molarity of a solution, which formula should you use to find the number of moles?

$\text{moles} = \text{Molarity} \times \text{Volume (L)}$

Question 1

Which of the following best describes the purpose of a stoichiometric calculation in solution chemistry?

Accepted Answer

To determine the amount of unknown compound produced or required using the given quantity and balanced equation coefficients.

Question 2

Given the reaction $2 \mathrm{Na} (s) + 2 \mathrm{H}_2\mathrm{O} (l) \rightarrow 2 \mathrm{NaOH} (aq) + \mathrm{H}_2 (g)$, how many moles of sodium hydroxide are produced when 0.75 moles of sodium react with excess water?

Accepted Answer

$1.5$ moles

Question 3

A student is given 16.2 g of magnesium metal to react with hydrochloric acid according to $\mathrm{Mg} (s) + 2 \mathrm{HCl} (aq) \rightarrow \mathrm{MgCl}_2 (aq) + \mathrm{H}_2 (g)$. What is the first step in determining the volume of 0.25 M HCl needed for complete reaction?

Accepted Answer

Convert grams of magnesium to moles using its molar mass.

Question 4

In the reaction $2 \mathrm{HBr} (aq) + \mathrm{Ca(OH)}_2 (aq) \rightarrow \mathrm{CaBr}_2 (aq) + 2 \mathrm{H}_2\mathrm{O} (l)$, what is the mole ratio of HBr to Ca(OH)$_2$?

Accepted Answer

$2:1$

Question 5

A solution contains 0.325 M HCl. How many milliliters are required to react completely with 16.2 g of magnesium metal? (Molar mass of Mg = 24.3 g/mol, reaction: $\mathrm{Mg} + 2 \mathrm{HCl} \rightarrow \mathrm{MgCl}_2 + \mathrm{H}_2$)

Accepted Answer

$5,265$ mL

Question 6

If 34.12 mL of HBr is required to neutralize 82.56 mL of 0.156 M Ca(OH)$_2$ according to $2 \mathrm{HBr} + \mathrm{Ca(OH)}_2 \rightarrow \mathrm{CaBr}_2 + 2 \mathrm{H}_2\mathrm{O}$, what is the molarity of the HBr solution?

Accepted Answer

$0.439$ M

Question 7

Which step in a stoichiometric calculation involves using the coefficients from the balanced equation?

Accepted Answer

Mole to mole comparison

Question 8

In the reaction $2 \mathrm{MnO}_4^- + 3 \mathrm{SO}_3^{2-} + 2 \mathrm{H}_2\mathrm{O} \rightarrow 2 \mathrm{MnO}_2 + 3 \mathrm{SO}_4^{2-} + 4 \mathrm{OH}^-$, how many moles of $\mathrm{SO}_3^{2-}$ are required to react with 0.50 moles of $\mathrm{MnO}_4^-$?

Accepted Answer

$0.75$ moles

Question 9

A chemist mixes 25.0 mL of 0.120 M MnO$_4^-$ (MW: 118.9 g/mol) with 32.0 mL of 0.140 M SO$_3^{2-}$ (MW: 80.07 g/mol). Using the reaction $2 \mathrm{MnO}_4^- + 3 \mathrm{SO}_3^{2-} + 2 \mathrm{H}_2\mathrm{O} \rightarrow 2 \mathrm{MnO}_2 + 3 \mathrm{SO}_4^{2-} + 4 \mathrm{OH}^-$, what is the theoretical yield of MnO$_2$ in grams?

Accepted Answer

$11.12$ g

Question 10

Which of the following is the correct sequence of steps for solving a solution stoichiometry problem?

Accepted Answer

Convert given to moles, use mole ratio, convert to desired units

Question 11

If 38.74 mL of 0.275 M H$_2$O reacts with excess sodium according to $2 \mathrm{Na} + 2 \mathrm{H}_2\mathrm{O} \rightarrow 2 \mathrm{NaOH} + \mathrm{H}_2$, how many moles of hydrogen gas are produced?

Accepted Answer

$0.00533$ moles

Question 12

Why is it important to use the coefficients from the balanced chemical equation in stoichiometric calculations?

Accepted Answer

They indicate the proportional relationship between reactants and products.

Question 13

A reaction requires 2 moles of HCl for every mole of Mg. If you have 0.5 moles of Mg, how many moles of HCl are needed?

Accepted Answer

$1.0$ moles

Question 14

In a neutralization reaction, what is the role of the acid and base?

Accepted Answer

The acid donates protons and the base accepts them, forming water and a salt.

Question 15

If you are given the volume and molarity of a solution, which formula should you use to find the number of moles?

Accepted Answer

$	ext{moles} = 	ext{Molarity} 	imes 	ext{Volume (L)}$

Question 16

A student needs to prepare 250 mL of 0.160 M NaOH solution. How many moles of NaOH are required?

Accepted Answer

$0.040$ moles

Question 17

Which of the following is a real-world application of stoichiometry in medicine?

Accepted Answer

Calculating the correct dosage of a drug based on patient body mass and reaction yield.

Question 18

If a solution contains 0.250 M HCl and you need 100 mL for a reaction, how many moles of HCl are present?

Accepted Answer

$0.025$ moles

Question 19

In the reaction $2 \mathrm{Na} + 2 \mathrm{H}_2\mathrm{O} \rightarrow 2 \mathrm{NaOH} + \mathrm{H}_2$, what is the limiting reactant if you have 1.0 mole of Na and 1.0 mole of H$_2$O?

Accepted Answer

Neither; both will run out at the same time.

Stoichiometry and Mole-to-Mole Calculations in GOB Chemistry

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