Q: A sample contains $$21.7\ \mathrm{g} of $$titanium (Ti). How many atoms of Ti are present? (Atomic mass of Ti = $$47.87\ \mathrm{g/mol}$$, Avogadro’s number $$= 6.022 \times 10$$^{23}$$\ \mathrm{mol}^{-1})$$

$$2.73 \times 10$$^{23}$$ atoms

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

A mole is $$6.022 \times 10$$^{23}$$ entities of a substance, such as atoms, molecules, or ions.

Question 1

Which of the following statements best describes the Law of Conservation of Matter?

Accepted Answer

The total quantity of matter remains constant when matter changes from one type to another, whether by chemical or physical change.

Question 2

Dalton’s atomic theory included several postulates. Which of the following is NOT one of Dalton’s original postulates?

Accepted Answer

Atoms can be converted into energy during chemical reactions.

Question 3

A sample of magnesium contains three isotopes: $$^{24}\mathrm{Mg} (78.99$$%, 23.985 amu), $$^{25}\mathrm{Mg} (10.00$$%, 24.986 amu), and $$^{26}\mathrm{Mg} (11.01$$%, 25.983 amu). What is the average atomic mass of magnesium? (Round to two decimal places.)

Accepted Answer

$$24.31\ \mathrm{amu}$$

Question 4

Which experiment provided the first direct evidence for the existence of the electron?

Accepted Answer

Thomson’s cathode ray tube experiment

Question 5

A neutral atom of $$^{35}\mathrm{Cl}$$ has:

Accepted Answer

17 protons, 18 neutrons, 17 electrons

Question 6

Which of the following best explains why the periodic table is organized by atomic number rather than atomic mass?

Accepted Answer

Atomic number reflects the number of protons, which determines the element’s identity and chemical properties.

Question 7

A sample contains $$21.7\ \mathrm{g} of $$titanium (Ti). How many atoms of Ti are present? (Atomic mass of Ti = $$47.87\ \mathrm{g/mol}$$, Avogadro’s number $$= 6.022 	imes 10$$^{23}$$\ \mathrm{mol}^{-1})$$

Accepted Answer

$$2.73 	imes 10$$^{23}$$ atoms

Question 8

Which of the following statements about isotopes is correct?

Accepted Answer

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

Question 9

Which of the following best describes a mole in chemistry?

Accepted Answer

A mole is $$6.022 	imes 10$$^{23}$$ entities of a substance, such as atoms, molecules, or ions.

Question 10

Which of the following is a property of metals as classified on the periodic table?

Accepted Answer

They are shiny, malleable, and good conductors of heat and electricity.

Question 11

Which scientist’s experiment led to the discovery of the atomic nucleus?

Accepted Answer

Ernest Rutherford’s gold foil experiment

Question 12

A certain element has two naturally occurring isotopes: $$^{10}\mathrm{B} (19.9$$%, 10.0129 amu) and $$^{11}\mathrm{B} (80.1$$%, 11.0093 amu). Calculate the average atomic mass of boron.

Accepted Answer

$$10.81\ \mathrm{amu}$$

Question 13

Which of the following best describes the difference between a chemical and a physical change, according to the law of conservation of matter?

Accepted Answer

Both chemical and physical changes conserve the total mass of matter.

Question 14

Which of the following is the correct symbol for an isotope of magnesium with 12 protons and 13 neutrons?

Accepted Answer

$$^{25}\mathrm{Mg}$$

Question 15

Which of the following statements about the structure of the atom is correct?

Accepted Answer

The nucleus contains most of the atom’s mass and is positively charged.

Question 16

If you have 0.55 moles of copper (Cu), what is the mass in grams? (Atomic mass of Cu = $$63.55\ \mathrm{g/mol})$$

Accepted Answer

$$34.95\ \mathrm{g}$$

Question 17

Which of the following best describes a metalloid?

Accepted Answer

An element that conducts heat and electricity moderately well and has properties of both metals and nonmetals.

Question 18

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

Accepted Answer

$$	ext{Number of neutrons} = 	ext{Mass number} - 	ext{Atomic number}$$

Question 19

Which of the following real-world examples best illustrates the law of definite proportions?

Accepted Answer

Calcium carbonate ($$\mathrm{CaCO}_3) $$always contains calcium, carbon, and oxygen in the same mass ratio, regardless of its source.

Atoms, Molecules, and Ions: A Deeper Look at Matter (Chemistry 1A Chapter 2 Study Notes)

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