Q: Which formula is used to calculate the relative atomic mass of an element with multiple isotopes?

$$\text{Relative Atomic Mass} = \sum (\text{Isotopic Mass} \times \text{Fractional Abundance})$$

Q: Which of the following best defines a mole in chemistry?

A mole is $$6.022 \times 10$$^{23}$$ particles of a substance.

Q: Which of the following is the correct formula to convert grams of a substance to moles?

$$\text{Moles} = \frac{\text{Grams}}{\text{Molar Mass}}$$

Q: Which of the following is the correct molecular formula for a compound with an empirical formula of $$\text{CH}_2\text{O}$$ and a molar mass of $$180\ \text{g/mol}$$?

$$\text{C}_6\text{H}_{12}\text{O}_6$$

Q: A student calculates the molar mass of $$\text{Al}_2\text{O}_3. $$Which calculation is correct?

$$2 \times 26.98 + 3 \times 16.00 = 101.96\ \text{g/mol}$$

Question 1

Which of the following best describes the difference between accuracy and precision in chemical measurements?

Accepted Answer

Accuracy refers to how close measurements are to the true value, while precision refers to how close measurements are to each other.

Question 2

A student measures the mass of a sample five times and obtains the following results: 2.01 g, 2.00 g, 2.02 g, 2.01 g, and 2.00 g. The true mass is 2.50 g. Which statement best describes the student's measurements?

Accepted Answer

The measurements are precise but not accurate.

Question 3

Which formula is used to calculate the relative atomic mass of an element with multiple isotopes?

Accepted Answer

$$	ext{Relative Atomic Mass} = \sum (	ext{Isotopic Mass} 	imes 	ext{Fractional Abundance})$$

Question 4

Which of the following best defines a mole in chemistry?

Accepted Answer

A mole is $$6.022 	imes 10$$^{23}$$ particles of a substance.

Question 5

What is the molar mass of $$	ext{Ca(OH)}_2$$?

Accepted Answer

$$74.10\ 	ext{g/mol}$$

Question 6

A compound contains 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen by mass. What is its empirical formula?

Accepted Answer

$$	ext{CH}_2	ext{O}$$

Question 7

Which of the following is the correct formula to convert grams of a substance to moles?

Accepted Answer

$$	ext{Moles} = \frac{	ext{Grams}}{	ext{Molar Mass}}$$

Question 8

A student dissolves 10.0 g of NaCl in water. What is the number of moles of NaCl present? ($$	ext{Molar mass of NaCl} = 58.44\ 	ext{g/mol})$$

Accepted Answer

$$0.171\ 	ext{mol}$$

Question 9

Which of the following statements about significant figures is correct?

Accepted Answer

All nonzero digits are significant.

Question 10

A sample contains $$3.01 	imes 10$$^{23}$$ molecules of water. How many moles of water are present?

Accepted Answer

$$0.50\ 	ext{mol}$$

Question 11

Which of the following is the correct molecular formula for a compound with an empirical formula of $$	ext{CH}_2	ext{O}$$ and a molar mass of $$180\ 	ext{g/mol}$$?

Accepted Answer

$$	ext{C}_6	ext{H}_{12}	ext{O}_6$$

Question 12

A chemist needs to prepare 0.25 mol of $$	ext{KCl}. $$What mass of $$	ext{KCl}$$ should be weighed out? ($$	ext{Molar mass of KCl} = 74.55\ 	ext{g/mol})$$

Accepted Answer

$$37.28\ 	ext{g}$$

Question 13

Which of the following best describes the empirical formula?

Accepted Answer

The empirical formula shows the simplest whole-number ratio of atoms in a compound.

Question 14

A student calculates the molar mass of $$	ext{Al}_2	ext{O}_3. $$Which calculation is correct?

Accepted Answer

$$2 	imes 26.98 + 3 	imes 16.00 = 101.96\ 	ext{g/mol}$$

Question 15

Which of the following is NOT a step in determining the empirical formula from percent composition?

Accepted Answer

Add the atomic numbers of each element.

Question 16

A sample of glucose ($$	ext{C}_6	ext{H}_{12}	ext{O}_6) $$contains 180 g. How many moles of glucose are present?

Accepted Answer

$$1.00\ 	ext{mol}$$

Question 17

Which of the following is the correct definition of Avogadro's number?

Accepted Answer

The number of particles in one mole of a substance.

Question 18

A student is given a sample containing $$1.20 	imes 10$$^{24}$$ molecules of $$	ext{CO}_2$$. How many moles of $$	ext{CO}_2$$ are present?

Accepted Answer

$$2.00\ 	ext{mol}$$

General Chemistry: Measurement, Moles, and Chemical Calculations Study Guide

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