Q: How many atoms are in $$2.00$$ moles of iron ($$\mathrm{Fe}$$)? (Avogadro’s number $$= 6.022 \times 10$$^{23}$$)

$$1.20 \times 10$$^{24}$$ atoms

Question 1

Which experiment provided the first direct evidence for the existence of atoms, as explained by Einstein and confirmed by Perrin?

Accepted Answer

Brownian motion observations

Question 2

Which law states that the total mass of substances does not change during a chemical reaction?

Accepted Answer

Law of Conservation of Mass

Question 3

A compound contains 16.0 g of oxygen and 2.0 g of hydrogen. What is the mass ratio of oxygen to hydrogen, and which law does this illustrate?

Accepted Answer

$$8:1$$, Law of Definite Proportions

Question 4

Which of the following is NOT a postulate of Dalton’s Atomic Theory?

Accepted Answer

Atoms of one element can change into atoms of another element during chemical reactions.

Question 5

Which experiment led to the discovery of the electron?

Accepted Answer

Cathode ray tube experiment

Question 6

What is the relative charge and approximate mass (in amu) of a neutron?

Accepted Answer

Charge: $$0$$, Mass: $$1.00866$$ amu

Question 7

An isotope of magnesium is represented as $$^{25}_{12}\mathrm{Mg}. $$How many neutrons does it contain?

Accepted Answer

$$13$$

Question 8

Which group in the periodic table contains the noble gases?

Accepted Answer

Group 8A

Question 9

A neutral atom of sulfur has an atomic number of $$16$$ and a mass number of $$32. $$How many protons, neutrons, and electrons does it have?

Accepted Answer

Protons: $$16$$, Neutrons: $$16$$, Electrons: $$16$$

Question 10

Which element is a metalloid and is commonly used in semiconductors?

Accepted Answer

Silicon

Question 11

Which of the following best describes the periodic law?

Accepted Answer

Elements are arranged in order of increasing atomic number, and elements with similar properties recur at regular intervals.

Question 12

Which main-group element is most likely to form a $$2+$$ ion?

Accepted Answer

Magnesium

Question 13

Calculate the atomic mass of an element with two isotopes: $$^{10}\mathrm{B} (19.9$$%, mass = 10.0129 amu) and $$^{11}\mathrm{B} (80.1$$%, mass = 11.0093 amu).

Accepted Answer

$$10.81$$ amu

Question 14

Which instrument is used to measure the masses of atoms and the percent abundances of isotopes?

Accepted Answer

Mass spectrometer

Question 15

How many atoms are in $$2.00$$ moles of iron ($$\mathrm{Fe}$$)? (Avogadro’s number $$= 6.022 	imes 10$$^{23}$$)

Accepted Answer

$$1.20 	imes 10$$^{24}$$ atoms

Question 16

A sample contains $$0.500$$ grams of carbon ($$\mathrm{C}). $$How many moles of carbon are present? (Molar mass of C $$= 12.01 g/$$mol)

Accepted Answer

$$0.0416$$ mol

Question 17

Which of the following statements about ions is correct?

Accepted Answer

Cations are positively charged and anions are negatively charged.

Question 18

Which of the following elements is a transition metal?

Accepted Answer

Iron

Question 19

If a neutral atom of chlorine ($$Z=17) $$gains one electron, what is the resulting ion and its charge?

Accepted Answer

$$\mathrm{Cl}^-$$, 1-$

Question 20

Which of the following best explains why the atomic mass of carbon is $$12.01 g/$$mol and not exactly $$12.00 g/$$mol?

Accepted Answer

Because the atomic mass is an average of all naturally occurring isotopes of carbon.

Chapter 2 Student Notes

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