Exam 1 (Ch E-2.5)

Question 1

Define the law of definite proportions

Answer 1

All samples of a given compound regardless of their source or how they were prepared will have the same proportion of their constituent elements.

Question 2

Define the law of conservation of mass

Answer 2

In chemical reactions matter is neither created nor destroyed.

Question 3

Define the law of multiple proportions

Answer 3

When elements A and B form different compounds, the masses of element B that combine with 1g of element A can be expressed in a ratio of small whole numbers.

Question 4

Describe Dalton’s theory

Answer 4

Atomic Theory
1) Each element is composed of tiny indestructible particles called atoms.

2) All atoms of the same element have the same mass and other properties than distinguish them from other elements.

3) Atoms combine in simple whole number ratios.

4) Atoms of 1 element can’t change into atoms of another element.

Question 5

What is the photoelectric effect?

Answer 5

The photoelectric effect explains the particle nature of light. It consists on the idea that many metals emit electrons when light is shined at them. The energy required to emit electrons depends on the frequency of light. A minimum threshold frequency needs to be reached to eject one electron. The intensity of the light doesn’t change the threshold frequency.

Question 6

What is precision?

Answer 6

How well several measurements of the same thing agree. “reproducible”

Question 7

What is accuracy?

Answer 7

Agreement of the measurements with the accepted value of the quantity.

Question 8

Are interior zeros significant?

Answer 8

yes

Question 9

Are leading zeros significant? (ex. 0.0028)

Answer 9

no

Question 10

Are trailing zeros significant? (ex. 76.000)

Answer 10

yes, they determine the precision of the instrument.

Question 11

Are trailing zeros before the d.p significant? (ex. 8400.5)

Answer 11

yes

Question 12

How should you round after addition or subtraction?

Answer 12

The answer should have the same number of decimal places and the input number with the least decimal places.

Question 13

How should you round after multiplication or division?

Answer 13

the answer should have the same number of sig figs as the input number with the least sig figs (ignoring exact values or constants).

Question 14

What is the formula for density?

Answer 14

D=m/v (g/cm^3)

Question 15

What is energy?

Answer 15

capacity to work

Question 16

What is work?

Answer 16

Action of a force through a distance.

Question 17

What is Kinetic energy?

Answer 17

Energy due to motion.

Question 18

What is potential energy?

Answer 18

energy that can be release through a chemical reaction.

Question 19

What is the difference between a theory and a law?

Answer 19

A law is s set of observations which will always be the same under the same conditions wheres a hypothesis is a model to explain why something happens.

Question 20

What is a pure substance?

Answer 20

A pure substance can consist of 1 element or 1 compound.

Question 21

What is a mixture?

Answer 21

A mixture is an impure substance. It can be a homogenous mixture –> difficult to separate or a heterogenous mixture –> easier to separate.

Question 22

What is the difference between an ion and an isotope?

Answer 22

An ion of an element has the same number of protons and neutrons but have lost or gained electrons. An isotope has the same number of protons but different number of neutrons.

Question 23

How do you calculate the average mass of an element?

Answer 23

(natural abundance/100) Mass of isotope 1 + Mass of isotope 2 (natural abundance/100)

Question 24

Define Cations and Anions

Answer 24

Cation - positive ion
Anion - Negative ion

Question 25

What is mass spectroscopy?

Answer 25

Technique that separates particles according to their mass using a magnetic field.

Question 26

How do you calculate the number of particles of an element using moles?

Answer 26

(Mass of sample/ molar mass of element) x (6.022x10^23/Moles)

Question 27

What is wavelength?

Answer 27

Distance between two peaks

Question 28

What is Amplitude of a wave?

Answer 28

Half distance between trough and peak.

Question 29

What is Frequency of a wave?

Answer 29

The number of times that a wave passes by a specific point per unit of time.

Question 30

What is the order of the electromagnetic spectrum (in decreasing wavelength)?

Answer 30

radiowave –> microwave–> infrared –> visible light –> ultraviolet –> x-rays –> gamma rays

Question 31

Describe interference patterns of waves

Answer 31

When two waves collide, one of two things can happen:
Destructive –> Peaks of waves don’t align (aren’t in phase) and they cancel each other, producing no light.
Constructive –> Peaks of both waves align (are in phase) and they merge, producing brighter light.

Question 32

What happens to the electrons as you increase the frequency in the photoelectric effect?

Answer 32

No electrons will be ejected until threshold frequency is reached. One it’s reached the excess energy (increased frequency) will be given to the electron as kinetic energy.

Question 33

Explain Bohr’s model of the atom

Answer 33

Bohr produced an early model of the atom in which there were orbits around the nucleus. Orbits have fixed energies. When electrons jumped between energy levels energy was emitted.

Question 34

What were the limitations to Bohr’s model of the atom?

Answer 34

• It didn’t take into account the wave nature of electrons.
• It didn’t explain why electrons didn’t crash into the nucleus.
• Couldn’t accurately predict behaviors of atoms bigger than hydrogen.

Question 35

How did they prove the electron’s interference pattern wasn’t caused by electrons bumping into each other?

Answer 35

They slowed down the experiment and observed one electron pass through the double slit and their still saw it produced an interference pattern due to diffraction if wave.

Question 36

What is the De Broglie principle?

Answer 36

Wavelength is inversely related to kinetic energy

Question 37

Describe Heisenberg’s Uncertainty principle

Answer 37

The more accurately you know the position the less accurately you know the velocity.

Question 38

What does the principal quantum number tell us?

Answer 38

The Principal quantum # (n) tells us the energy level and size of the orbitals. It can be any whole number bigger than zero. We can identify it by looking at the row # in the periodic table.

Question 39

What does the angular momentum quantum number tell us?

Answer 39

The angular momentum quantum # (l) tells us the shape of the orbitals. It can be any number from zero to n-1. You can find l by looking at the groups on the periodic table.

0=s
1=p
2=d
3=f

Question 40

What does the magnetic quantum number tell us?

Answer 40

The magnetic quantum # (ml) tells us the 3d orientation of the orbitals. It can be any number between -l and +l.

Question 41

What does the spin quantum number tell us?

Answer 41

The spin # (ms) tells us the orientation of the electron in the orbital. It can be +1/2 or -1/2

Question 42

Why is the wave nature of matter not important for a baseball?

Answer 42

The De Broglie wavelength of a baseball would be too small (to be observed) because of the big mass and slow velocity of the ball.

Question 43

What does it mean in terms of energy is ΔE<0?

Answer 43

It means that the atom is emitting energy. It happens when the electron falls from a higher energy level to a lower energy level.

Question 44

What does it mean in terms of energy is ΔE>0?

Answer 44

It means that the electron is absorbing (gaining) energy. This happens when an electron goes from a lower energy level to a higher energy level.

Question 45

What are the differences between Bohr’s model of the atom and the quantum mechanical model of the atom?

Answer 45

Bohr suggested a deterministic model of the atom in which electrons were found found in orbits surrounding the nucleus. The quantum mechanical model of the atom is more probabilistic and suggests a probability density map of orbitals where the electrons are likely to be found.

Question 46

Is Bohr’s model consistent with Heisenberg’ uncertainty principle?

Answer 46

No. Because with Bohr’s model you can know both the position and motion of an electrons which Heisenberg’s principle suggests we can’t.