Q: How many atoms are present in $$2.45$$ mol of copper?

$$1.38 \times 10$$^{24}$$ atoms

Q: Which of the following is the correct formula for calculating the number of neutrons in an atom?

$$\text{Number of neutrons} = \text{Mass number} - \text{Atomic number}$$

Question 1

Which experiment provided the first direct evidence for the existence of atoms as discrete particles?

Accepted Answer

Brownian motion observed by Einstein in 1905

Question 2

According to the law of definite proportions, which of the following statements is correct?

Accepted Answer

The mass ratio of elements in a compound is always the same, regardless of the sample's origin.

Question 3

A sample of water decomposes to produce 18.0 g of water, 16.0 g of oxygen, and 2.0 g of hydrogen. What is the mass ratio of oxygen to hydrogen in water?

Accepted Answer

$$8:1$$

Question 4

Which of the following best describes the result of Rutherford's gold foil experiment?

Accepted Answer

Most alpha particles passed straight through, but a few were deflected at large angles, indicating a small, dense, positively charged nucleus.

Question 5

Which subatomic particle has a mass approximately $$1/1836$$ that of a proton?

Accepted Answer

Electron

Question 6

An isotope of chlorine consists of $$75.77\%$$ $$^{35}\mathrm{Cl} ($$mass $$= 34.97$$ amu) and $$24.23\%$$ $$^{37}\mathrm{Cl} ($$mass $$= 36.97$$ amu). What is the average atomic mass of chlorine?

Accepted Answer

$$35.5$$ amu

Question 7

Which of the following statements about ions is correct?

Accepted Answer

A cation is formed when an atom loses electrons.

Question 8

Which law states that when two elements form more than one compound, the masses of one element that combine with a fixed mass of the other are in ratios of small whole numbers?

Accepted Answer

Law of Multiple Proportions

Question 9

A neutral atom of sodium ($$^{23}\mathrm{Na}) $$has 11 protons. How many electrons and neutrons does it have?

Accepted Answer

11 electrons, 12 neutrons

Question 10

Which experiment determined the charge of the electron?

Accepted Answer

Millikan's oil drop experiment

Question 11

How many atoms are present in $$2.45$$ mol of copper?

Accepted Answer

$$1.38 	imes 10$$^{24}$$ atoms

Question 12

Which of the following is a property of metals?

Accepted Answer

Good conductor of heat and electricity

Question 13

A sample of carbon monoxide contains $$2.67 g of $$oxygen for every $$1.33 g of $$carbon. What is the mass ratio of oxygen to carbon in this compound?

Accepted Answer

$$2:1$$

Question 14

Which of the following best explains why atoms of the same element can have different masses?

Accepted Answer

They have different numbers of neutrons.

Question 15

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

Accepted Answer

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

Question 16

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 17

If a magnesium atom has 12 protons, 12 neutrons, and 10 electrons, what is its charge?

Accepted Answer

$$+2$$

Question 18

Which of the following best describes the modern periodic table?

Accepted Answer

Elements are arranged in order of increasing atomic number.

Question 19

Which of the following is the correct value for Avogadro's number?

Accepted Answer

$$6.022 	imes 10$$^{23}$$

Question 20

A sample contains $$0.265 g of $$carbon. How many moles of carbon are present? (Atomic mass of C = $$12.01 g/$$mol)

Accepted Answer

$$0.0221$$ mol

Atoms, Elements, and the Foundations of Modern Chemistry

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