Exam 1 Review!

Homework

100

Sig Figs 0.0030 0.1044 43,069 0.00004715 57,600

2 4 5 4 5

200

FREE POINTS!

FREE POINTS!

300

Magnesium oxide (MgO) forms when the metal burns in air. a) If 1.25 g of MgO contains 0.754 g of Mg, what is the mass ratio of magnesium to oxide? b) How many grams of Mg are in 534 g of MgO?

a) 0.754/1.25=0.603 b)534 g MgO * (0.603 g Mg/1 g MgO)=322 g Mg

400

Earth's surface area is 5.10e8 km2, its crust has a mean thickness of 35 km and a mean density of 2.8 g/cm3. The two most abundant elements in the crust are oxygen (4.55e5 g/t, where t stands for "metric ton"; 1t=1000 kg) and silicon (2.72e5 g/t), and the two rarest nonradioactive elements are ruthenium and rhodium, each with an abundance of 1e-4 g/t. What is the total mass of each of these elements in Earth's crust?

Vol of Crust=(35 km)(5.1e8 km2)=1.785e10 km3 1.785e10 km3 * (1000 m/1 km)^3*(1 cm/0.01 m)^3=1.785e25 cm3 Mass of Crust=1.785e25 cm3*(2.8 g/1 cm3)*(1kg/1000g)*(1t/1000 kg)=4.998e19 t Mass of Oxygen=4.998e19 t * (4.55e5 g Oxygen/1 t)=2.3e25 g Oxygen Mass of Silicon=4.998e19 t * (2.72e5 g silicon/1 t)=1.4e25 g silicon Mass of ruthenium=mass of rhodium=(4.998e19 t) * (1e-4 g element/ 1 t)=5e15 g each of ruthenium and rhodium

500

Chlorine has two naturally occurring isotopes, Cl-35 (mass=34.9689 amu) and Cl-37 (mass=36.9659 amu). If chlorine has an atomic mass of 35.4527 amu, what is the percent abundance of each isotope?

Atomic Mass=(Isotopic Mass of Cl-35)*(Fractional Abundance)+(Isotopic Mass of Cl-37) *(Fractional Abundance) 35.4527=(35.9689)x+36.9659(1-x) x=0.75774 Cl-35: 75.774% Cl-37: 24.226%

Ch 2

100

Magnesium and nitrogen Iodine and cadmium Sulfur and cesium

Magnesium Nitride Cadmium Iodide Cesium sulfide

200

What ions do the elements form? Iodine, calcium, aluminum

I-, Ca2+, Al3+

300

Cation & Anion

cation: metal atom loses 1+ electron, becoming POSITIVELY charged ion anion: nonmetal atom gains 1+ electron, becoming NEGATIVELY charged ion

400

Group Names

1A Alkali Metals 2A Alkaline Earth Metals 7A Halogens 8A Noble Gases

500

Ionic vs. Covalent Compounds

Ionic Compounds: transferring electrons from one element to another Covalent Compounds: sharing electrons between atoms of different elements

Theories

100

Properties & States of Matter

Physical Prop:characteristics a substance shows by itself, w/o changing into or interacting w/ another substance ex. melting point, density Physical Change: when a substance alters its physical properties, NOT its composition ex. ice melts Chemical Prop:characteristics a substance shows as it changes into or interacts w/ another substance ex. flammability, corrosiveness Chemical Change: when a substance is converted into a different substance ex. decomposition rxn, combustion rxn States of Matter: Solid, Liquid, Gas

200

Atomic Overview: Element, Molecule, Compound, Mixture

Element: simplest type of matter w/ unique physical & chemical properties, consists of only one kind of atom Molecule: independent structure of 2+ atoms bound together Compound: 2+ different elements that are bonded chemically Mixture: 2+ substances (elements/compounds) that are physically intermingled

300

Precision vs. Accuracy

Precision: reproducibility, refers to how close the measurements in a series are to each other Accuracy: refers to how close each measurement is to the actual value

400

Law of Mass Conservation, Law of Definite Composition, Law of Multiple Proportions

1) Total mass of substances does not change during a chemical rxn 2) No matter what its source, a particular compound is composed of the same elements in the same parts (fractions) by mass. (Mass fraction, mass percent) 3) If elements A & B react to form 2 compounds, the different masses of B that combine w/ a fixed mass of A can be expressed as a ratio of small whole numbers.

500

Structure of the Atom

An atom is an electrically neutral, spherical entity. In the center of an atom is a positively charged nucleus surrounded by one or more negatively charged electrons. p48

Experiments/Examples

100

Naked I.C.E. Experiment

ICE=Internal Combustion Engine. Plastic bottle with 2 metal pieces sticking out from either side. Contained small amount of ethanol, which acted as fuel. When tesla coil touched the metal ("lightening"), produced flame. Flame (color) ignited by gas molecules from liquid. High pressure caused the cork to pop off. Combustion Rxn. CH3CH2OH(l)+ O2 (g) ---> CO

200

Fish Tank Experiment

Fish Tank with dry ice. Blew bubbles into it. What happened? CO2 heavier than air? Placed candle into. Flammable in tank?

300

Fan Experiment (Sterling Engine)

You tell me!

400

1.00 g block of gold (p=19.32 g/cm3) is hammered into a sheet. Dimensions of the sheet are 8 ft by 5 ft. 25.4 mm=1 in. What is the thickness of the sheet in nm?

Vol=8*5*h=(40 ft2) * h 40 ft2 * (12 in/1 ft)^2* (2.54 cm/1 in)^2=37,161.22 cm2 Density=Mass/Volume 19.32 g/cm3=(1.00 g)/Volume Volume=0.0518 cm3=(37161.22 cm2)*h h=1.39e-6 cm=13.9 nm

500

Rutherford Alpha-Scattering Experiment

Experiment: Small, dense, positively charged alpha particles emitted from radium aimed at gold foil. Circular, zinc-sulfide screen registered the deflection (scattering) of the alpha particles by emitting light flashes when the particles struck it. Results: Only 1/20,000 deflected by more than 90 degrees. Conclusion: Only few alpha particles were being repelled by something small, dense, and positive within gold atoms. Atom is mostly space occupied by electrons. In the center is a tiny region, which Rutherford called the nucleus. Nucleus contains all the positive charge and essentially all the mass of the atom.

Notes

100

Intensive & Extensive Property

Intensive Property: independent of amount ex. density, temperature Extensive Property: depends on amount ex. mass, volume, heat (cup vs. pot)

200

Significant Figure Rules: Mult/Div & Add/Subt

Mult/Div: Final answer has same SFs as # w/ fewest SFs in calculation ex. (3.0)*(4.127)=12 Add/Subt: Answer must contain same # of decimal places as the measurement with the fewest decimal places ex. 83.5+23.28=106.8

300

Atomic Theory (2/4)

1) All normal matter is composed of atoms. An atom is the smallest body/unit that retains identity of that element. 2) Atoms of one element cannot be converted to other atoms/elements in a chemical reaction. 3) All atoms of an element have same number of protons. All neutral atoms of an element have the same number of electrons. All atoms of an element exhibit same chemistry. 4) Compounds are formed by the chemical combination of set ratios.

400

Mass Number, Atomic Number, Isotopes

Mass Number= p + n Atomic Number = p Isotopes: differ in the number of neutrons

500

Periodic Table Trends: Metals, Nonmetals, Metalloids

Metals: left & middle Nonmetals: right Metalloids: between metals and nonmetals (lie along the staircase line) Elements in a GROUP (vertical) have SIMILAR chemical properties. Elements in a PERIOD (horizontal) have DIFFERENT chemical properties.