Matter and Changes
Classify each as an element, compound, homogeneous mixture, or heterogeneous mixture:
air, pure water, iron, and granite.
Air: homogeneous mixture
Pure water: compound
Iron: element
Granite: heterogeneous mixture.
How many significant figures are in each measurement: 4.52, 0.0569, and 8.9210?
4.52 = 3
0.0569 = 3
8.9210 = 5
What metric prefix represents 10−310^{-3}, and what is its symbol?
milli-, symbol m
Which subatomic particles are found in the nucleus, which are found outside the nucleus, and what are their charges?
Nucleus - Protons +1 and Neutrons 0
Outside nucleus - Electrons −1.
According to Dalton's atomic theory, what is true about the atoms that make up a compound?
Compounds contain atoms of different elements combined in fixed ratios; a given compound always has the same kinds and ratio of atoms.
Name all seven homonuclear diatomic elements and give their formulas.
H₂, N₂, O₂, F₂, Cl₂, Br₂, I₂
Classify each as a physical or chemical property: the color of copper, the density of gold, and the tendency of gasoline to burn.
Color: physical property
Density: physical property
Flammability: chemical property.
A set of measurements are very close to one another but not close to the accepted value. Are the measurements accurate, precise, both, or neither?
Precise, but not accurate. Precision describes how closely repeated measurements agree; accuracy describes closeness to the correct/accepted value.
Convert 3.5 km to meters and report the answer in scientific notation.
3.5×103 m
An atom has a mass number of 23 and an atomic number of 11. How many protons and neutrons does it contain?
11 protons and 12 neutrons. Atomic number = number of protons; neutrons = mass number − atomic number = 23 − 11 = 12
A particular compound always contains the same elements in the same proportions. What law does this illustrate?
The Law of Definite Proportions
Give the empirical formula of hydrogen peroxide, H₂O₂.
HO. Divide both subscripts by their common factor of 2
Classify each as a physical or chemical change: ice melting, sugar dissolving in water, and iron rusting.
Melting: physical
Dissolving: physical
Rusting: chemical
Evaluate 12.11 + 18.0 + 1.013 and report the answer with the correct precision.
31.1
Addition/subtraction is limited by the measurement with the fewest decimal places; 18.0 has one decimal place.
Convert 75.0 inches to feet using dimensional analysis.
6.25 ft
Two atoms have the same number of protons but different numbers of neutrons. What are they called, and what remains the same about their identity?
Isotopes. They are isotopes of the same element because they have the same number of protons/atomic number, but they have different mass numbers because their neutron counts differ.
H₂O and H₂O₂ contain the same two elements but in different ratios. What law does this illustrate?
The Law of Multiple Proportions
Name both compounds: CO and CO₂.
CO = carbon monoxide
CO₂ = carbon dioxide
Which of these are intensive properties and which are extensive properties: mass, volume, temperature, and density?
Intensive: temperature and density
Extensive: mass and volume
Evaluate 4.56 × 1.4 using the correct number of significant figures.
6.4
The calculator result is 6.384, but multiplication/division is limited by the number with the fewest significant figures. Since 1.4 has two sig figs, the result has two.
A metal has a density of 7.8 g/mL and a volume of 3.0 mL. What is its mass?
23 g
A chlorine atom has 17 protons and 17 electrons. It gains one electron. What ion forms, is it a cation or an anion, and how many protons and electrons does it now have?
Cl⁻ is an anion with 17 protons and 18 electrons.
What do elements in the same vertical column of the periodic table have in common, and what are these columns called?
They are called groups, and elements within a group have similar properties. Columns are called groups
Using the Stock system, name Fe₂O₃. What charge does the iron ion have?
Iron(III) oxide
Fe³⁺
Three O²⁻ ions give −6 total, so two Fe ions must total +6; each Fe is +3.
A sample contains liquid water and visible pieces of ice. Is it a pure substance or a mixture? Is its composition homogeneous or heterogeneous? If the ice melts, is that a physical or chemical change?
Pure substance (H₂O)
Heterogeneous because two distinct phases are present
Melting is a physical change.
Evaluate 479.1 ÷ 0.082 - Report the answer in scientific notation using the correct number of significant figures.
5.8 × 10³
479.1 has four significant figures and 0.082 has two, so the result must contain two significant figures.
What is the mathematical relationship between density, mass, and volume? Rearrange it to show how you would solve for all three quantities.
m=dV
d=m/V
V=m/d
* Remember the density triangle *
An element has two naturally occurring isotopes: 11.0093 amu with 80.22% abundance and 10.0129 amu with 19.78% abundance. (a) Calculate its average atomic mass. (b) Identify the element. (c) In a sample of 100 atoms, approximately how many would have masses of 11.0093 amu, 10.0129 amu, and exactly 10.81 amu?
(a) ≈10.81 amu. (b) Boron. (c) ≈80 atoms at 11.0093 amu, ≈20 atoms at 10.0129 amu, and 0 atoms at exactly 10.81 amu. The 10.81 amu value is a weighted average, not the mass of an individual boron atom.
Using only their positions on the periodic table, predict the charges of the ions formed by a Group 1A metal, a Group 2A metal, aluminum in Group 3A, and oxygen in Group 6A.
Group 1A: +1
Group 2A: +2
Al: +3
Oxygen: −2
Write the correct formula for ammonium sulfite.
(NH₄)₂SO₃