Q: Which of the following best describes a mole?

A quantity equal to $$6.022 \times 10$$^{23}$$ items, which relates the atomic scale to the human scale.

Question 1

Which of the following best explains why significant figures are important in chemical calculations?

Accepted Answer

They indicate how many digits in a measurement are trustworthy based on the precision of the instruments used.

Question 2

Given the reaction $$4 \mathrm{NH}_3 + 5 \mathrm{O}_2 \rightarrow 4 \mathrm{NO} + 6 \mathrm{H}_2\mathrm{O}$$, how many moles of $$\mathrm{O}_2$$ are required to completely react with $$8$$ moles of $$\mathrm{NH}_3$$?

Accepted Answer

$$10$$ moles

Question 3

A student adds $$1.034 g $$and $$0.21 g $$and then multiplies the sum by $$3.00. $$According to significant figure rules, what is the correct way to report the final answer?

Accepted Answer

$$3.73$$

Question 4

Which of the following is the correct balanced equation for the reaction between ammonia and oxygen to form nitric oxide and water?

Accepted Answer

$$4 \mathrm{NH}_3 + 5 \mathrm{O}_2 \rightarrow 4 \mathrm{NO} + 6 \mathrm{H}_2\mathrm{O}$$

Question 5

What is the percent by mass of iron in $$\mathrm{Fe}_2(\mathrm{SO}_4)_3$$? (Atomic masses: Fe = $$55.85$$, S = $$32.06$$, O = $$16.00)$$

Accepted Answer

$$27.92\%$$

Question 6

If you have $$1.00 g of $$acetic acid ($$\mathrm{CH}_3\mathrm{COOH}$$), how many grams of methanol ($$\mathrm{CH}_3\mathrm{OH}) $$are needed to completely react with it according to the equation $$\mathrm{CH}_3\mathrm{COOH} + \mathrm{CH}_3\mathrm{OH} \rightarrow \mathrm{CH}_3\mathrm{COOCH}_3 + \mathrm{H}_2\mathrm{O}$$? (Molar masses: $$\mathrm{CH}_3\mathrm{COOH} = 60.05 g/$$mol, $$\mathrm{CH}_3\mathrm{OH} = 32.04 g/$$mol)

Accepted Answer

$$0.534 g$$

Question 7

Which of the following statements about balancing chemical equations is correct?

Accepted Answer

The number of atoms of each element must be the same on both sides of the equation.

Question 8

What is the formula weight (in amu) of $$\mathrm{Fe}_2(\mathrm{SO}_4)_3$$?

Accepted Answer

$$399.88$$ amu

Question 9

How many molecules are in $$2.00$$ moles of water?

Accepted Answer

$$1.2044 	imes 10$$^{24}$$

Question 10

A chemist has $$10.0 g of$$ $$\mathrm{Fe}_2(\mathrm{SO}_4)_3. $$How many grams of iron are present in this sample? (Molar mass of $$\mathrm{Fe}_2(\mathrm{SO}_4)_3 = 399.88 g/$$mol, Fe = $$55.85 g/$$mol)

Accepted Answer

$$2.79 g$$

Question 11

Which of the following best describes a mole?

Accepted Answer

A quantity equal to $$6.022 	imes 10$$^{23}$$ items, which relates the atomic scale to the human scale.

Question 12

In the reaction $$2 \mathrm{H}_2(g) + \mathrm{O}_2(g) \rightarrow 2 \mathrm{H}_2\mathrm{O}(l)$$, if you start with $$4.00 g of$$ $$\mathrm{H}_2 ($$molar mass $$2.016 g/$$mol) and excess $$\mathrm{O}_2$$, how many grams of water can be produced? (Molar mass $$\mathrm{H}_2\mathrm{O} = 18.02 g/$$mol)

Accepted Answer

$$35.7 g$$

Question 13

Which of the following is the correct sequence for solving a stoichiometry problem involving mass-to-mass conversion?

Accepted Answer

Convert mass of reactant to moles, use mole ratio from balanced equation, convert moles of product to mass.

Question 14

A reaction requires $$0.500$$ mol of $$\mathrm{O}_2. $$How many molecules of $$\mathrm{O}_2 is $$this?

Accepted Answer

$$3.011 	imes 10$$^{23}$$

Question 15

Which of the following is NOT a correct rule for balancing chemical equations?

Accepted Answer

The number of molecules must be the same on both sides.

Question 16

If $$1$$ mole of $$\mathrm{Fe}_2(\mathrm{SO}_4)_3$$ contains $$2$$ moles of Fe, how many moles of Fe are in $$0.250$$ moles of $$\mathrm{Fe}_2(\mathrm{SO}_4)_3$$?

Accepted Answer

$$0.500$$ moles

Question 17

A student is asked to balance the equation $$\mathrm{C}_2\mathrm{H}_6 + \mathrm{O}_2 \rightarrow \mathrm{CO}_2 + \mathrm{H}_2\mathrm{O}. $$Which element should they leave for last when balancing?

Accepted Answer

Oxygen

Question 18

Which of the following best describes the difference between formula weight and molecular weight?

Accepted Answer

Formula weight applies to all compounds, while molecular weight is only for molecules.

Question 19

Why is it recommended to avoid rounding intermediate results in multi-step calculations involving significant figures?

Accepted Answer

Rounding intermediate results can introduce cumulative errors, reducing the accuracy of the final answer.

Reactions and Stoichiometry: Study Notes

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