Q: Which of the following is the correct formula for calculating the atomic mass of an element with two isotopes?

$$\text{Atomic mass} = (\text{fraction}_1 \times \text{mass}_1) + (\text{fraction}_2 \times \text{mass}_2)$$

Q: A sample contains 4.0 g of helium. How many moles of helium are present? (Molar mass of He = 4.0 g/mol)

$$4.0 \text{ g} \times \frac{1 \text{ mol}}{4.0 \text{ g}} = 1.0 \text{ mol}$$

Q: How many atoms are present in 0.25 mol of sodium? ($$N_A = 6.022 \times 10$$^{23}$$ atoms/mol)

$$0.25 \text{ mol} \times 6.022 \times 10$$^{23}$$ \text{ atoms/mol} = 1.51 \times 10$$^{23}$$ \text{ atoms}$$

Q: A sample of silicon has a mass of 28.09 g. How many moles of silicon are present? (Molar mass of Si = 28.09 g/mol)

$$28.09 \text{ g} \div 28.09 \text{ g/mol} = 1.00 \text{ mol}$$

Q: Which of the following statements about Avogadro's number is correct?

Avogadro's number is $$6.022 \times 10$$^{23}$$ and represents the number of particles in 1 mole of a substance.

Q: A student is given a 32.07 g sample of sulfur. How many moles of sulfur are present? (Molar mass of S = 32.07 g/mol)

$$32.07 \text{ g} \div 32.07 \text{ g/mol} = 1.00 \text{ mol}$$

Question 1

Which of the following best describes a homogeneous mixture?

Accepted Answer

A mixture in which the components are distributed uniformly throughout, so the composition is the same everywhere.

Question 2

Which of the following statements about atoms and ions is correct?

Accepted Answer

A cation is an atom that has lost electrons and thus has a positive charge.

Question 3

Which of the following is the correct formula for calculating the atomic mass of an element with two isotopes?

Accepted Answer

$$	ext{Atomic mass} = (	ext{fraction}_1 	imes 	ext{mass}_1) + (	ext{fraction}_2 	imes 	ext{mass}_2)$$

Question 4

A sample contains 4.0 g of helium. How many moles of helium are present? (Molar mass of He = 4.0 g/mol)

Accepted Answer

$$4.0 	ext{ g} 	imes \frac{1 	ext{ mol}}{4.0 	ext{ g}} = 1.0 	ext{ mol}$$

Question 5

Which of the following best describes an element?

Accepted Answer

A pure substance that cannot be separated into simpler substances by a chemical process.

Question 6

How many atoms are present in 0.25 mol of sodium? ($$N_A = 6.022 	imes 10$$^{23}$$ atoms/mol)

Accepted Answer

$$0.25 	ext{ mol} 	imes 6.022 	imes 10$$^{23}$$ 	ext{ atoms/mol} = 1.51 	imes 10$$^{23}$$ 	ext{ atoms}$$

Question 7

A sample of silicon has a mass of 28.09 g. How many moles of silicon are present? (Molar mass of Si = 28.09 g/mol)

Accepted Answer

$$28.09 	ext{ g} \div 28.09 	ext{ g/mol} = 1.00 	ext{ mol}$$

Question 8

Which of the following statements about Avogadro's number is correct?

Accepted Answer

Avogadro's number is $$6.022 	imes 10$$^{23}$$ and represents the number of particles in 1 mole of a substance.

Question 9

A neutral atom of chlorine has an atomic number of 17 and a mass number of 35. How many neutrons does it have?

Accepted Answer

$$35 - 17 = 18$$ neutrons

Question 10

Which of the following is a correct statement about isotopes?

Accepted Answer

Isotopes of an element have the same number of protons but different numbers of neutrons.

Question 11

A student is given a 32.07 g sample of sulfur. How many moles of sulfur are present? (Molar mass of S = 32.07 g/mol)

Accepted Answer

$$32.07 	ext{ g} \div 32.07 	ext{ g/mol} = 1.00 	ext{ mol}$$

Question 12

Which of the following best describes a compound?

Accepted Answer

A substance composed of two or more elements chemically combined in fixed proportions.

Question 13

Which of the following is the correct relationship for the number of neutrons in an atom?

Accepted Answer

$$	ext{Number of neutrons} = 	ext{mass number} - 	ext{atomic number}$$

Question 14

A sample contains $$5.47 	imes 10$$^{21}$$ atoms of silicon. How many moles of silicon are present? (N_A = 6.022$$ 	imes $$10^{23}$$ atoms/mol)

Accepted Answer

$$\frac{5.47 	imes 10$$^{21}$$}{6.022 	imes 10$$^{23}$$} = 0.00909 	ext{ mol}$$

Question 15

Which of the following is a correct statement about the states of matter?

Accepted Answer

Solids have a definite shape and volume.

Question 16

A student has 18.0 g of helium. How many moles of helium does this represent? (Molar mass of He = 4.0 g/mol)

Accepted Answer

$$18.0 	ext{ g} \div 4.0 	ext{ g/mol} = 4.5 	ext{ mol}$$

Question 17

Which of the following is the best example of a heterogeneous mixture?

Accepted Answer

Salad with lettuce, tomatoes, and cucumbers

Question 18

Which of the following is true about the mass number of an atom?

Accepted Answer

It is the sum of the number of protons and neutrons in the nucleus.

Question 19

Which of the following is the correct definition of a molecule?

Accepted Answer

A combination of two or more atoms held together by chemical bonds.

General Chemistry Study Notes: Chapter 1 – Atoms and Matter

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