Test I – Chemistry Flashcard

Dimensional Analysis
A method of conversion using the relation between units of measurement 
Dimensional Analysis Problem: Convert 6.2 grams to ounces 

1 g=0.035274oz

 

6.2g(0.035274oz/1g)=0.2186988oz

 

0.22 oz in 6.2 g

Dimension Analysis Problem: meters/second to miles/hour

Convert 18 m/s to mi/hr

.001 km=1m

1 km=0.621371 mi

1 min=60 s

60 min=1 hr

 

18m(.001km/1m)(0.621371mi/1km)=0.01118468 mi/s

0.01118468 mi/s (60s/1min)(60mins/1hr)=40.264848 mi/hr

4.0 x 10^1 mi/hr

Density
A physical property; mass divided by volume (D=M/V)

Density Problem: 

What is the volume of a piece of aluminum with a mass of  0.002 g?

(Density of aluminum is 2.7 g/cc)

D=M/V

 

2.7 g/cc=0.002g/V

 

V=0.002g/2.7g/cc

V=0.0007407

V=7 x 10^-4

Dimensional Analysis Problem: 

Convert 6 square inches to square centimeters

1 in=2.54 cm

 

6 in^2 (2.54cm/1 in)^2=51.8616 cm^2

 

50 cm^2

Density Problem: 

Find the mass of a piece of steel with a volume of 6.8 cc

 

(Density of steel is 7.85g/cc)

D=M/V

 

7.85g/cc=M/6.8cc

M=53.38g

M=53g

Pure Substance
A substance that is homogenous and cannot be separated by physical means; compounds, elements
Element
A substance containing only one type of atom; hydrogen, oxygen
Compound
A substance containing two or more elements that can be separated by chemical, but not physical, change; water, carbon dioxide
Mixture
A combination of substances that can be separated through physical means; salt water, a salad 
Heterogeneous Mixture
A mixture in which the different properties of the substances are visible; salad
Homogeneous Mixture
A mixture in which the different properties of the substances are not visible; salt water
Characteristic Properties of Pure Substances
Density, boiling point, melting point, solubility, color, etc
Chemical Property vs Physical Property
A chemical property can only be observed through a chemical change or reaction, whereas a physical property can be observed without changing the matter’s composition
Chemical Change vs Physical Change
A chemical change involves the rearrangement of atoms to form one or more new substances with different properties, whereas a physical change affects the form of a substance rather than its composition;
Law of Conservation
Matter is always conserved. The matter before a reaction is equal to the matter after a reaction.;

Application of the Law of Conservation:;

;

Two substances react. There are 6.3 grams of substance A, and the reaction of substances A and B results in 9.7 grams of substance C. How many grams of substance B were involved in the reaction?;

;

6.3 g+ x g=9.7 g

x=3.4g

;

3.4 g of substance B

Dalton’s Postulates

1. All matter is composed of small, indivisible particles called atoms.

2. All atoms of a given element are identical in mass and properties. 

3.  Compounds are formed by a combination of two or more atoms in definite arrangements in the ratio of small whole numbers. 

4. Atoms are not created, destroyed or converted into other kinds of atoms during chemical reactions.  They are simply rearranged into new compounds.


 

Protons
Positively charged subatomic particle inside of the nucleus
Neutron
Subatomic particle inside of the nucleus with no charge
Electron
Negatively charged subatomic particle orbiting nucleus in the electron cloud
Atoms vs Ions

An atom has no charge, so number p+=number e-

An ion is charged either positively or negatively. An ion of an element has more (neg ion) or less (pos ion) electrons than an atom of that element (the number of protons does not change, because the number of protons identifies the element) 

AMU
A unit of mass used to express atomic weights. It is equal to the weight of 1/12 of a carbon-12 atom
Isotopic Abundance
The abundance of an isotope in nature as compared to other isotopes of that element

Isotopic Abundance Problem: 

In element X, there are two different isotopes. X-13 has an isotopic abundance of 93.456% and X-12 has an isotopic abundance of 6.544%. What is the atomic mass of this element? 

13x.93456+12x.006544=12.227808

 

Atomic Mass of 12.227808 amu

How to determine whether isotopes are of the same element
Number of protons (or, if a neutral atom, electrons) 

Use Area of Aluminum Foil Lab: 

Determine the area of a piece of aluminum foil with a mass of 1.78 g

 

D=2.7g/cc

 

2.7g/cc=1.78g/V

V=1.78g/2.7/cc

V=0.6592593 cc

V=0.66cc

Isotopes
Variants of an element wherein the number of neutrons (and mass number) are different but the number of protons remains the same
Forms of Electromagnetic Radiation (from Left to Right)
Radio, Microwave, Infrared, Visible (ROYGBIV), Ultraviolet,  X-Ray, Gamma Ray
From High to Low Energy on the Electromagnetic Spectrum

-Frequency Decreases

-Wavelength Increases

Law of Multiple Proportions
When two elements can combine to form more than one compound the amounts of one of them that combines with a fixed amount of the other will exhibit a simple multiple relation.
Rutherford’s Experiment (Gold Foil)
Rutherford aimed alpha particles at a piece of gold foil, expecting them all to pass through. He was surprised to find that some of them were deflected back. This was because they hit the dense, positive nucleus; this discovery changed the model of the atom.;
Thomson’s Model of the Atom 
Thomson created the plum pudding model of the atom: a positively charged mass with negatively charged particles dispersed throughout
Electron Excitation in Relation to Absorption and Emission 
When an atom absorbs energy in the form of photons (light), an electron can gain enough energy to get excited and move to another energy level. When an electron drops to a lower energy level, this corresponds with the emission of light. 

How to Use the Formula C=wf

(And an example problem: What is the frequency of a photon of light with the wavelength of 600 nm?

speed of light=(wavelength)(frequency)

speed of light=3.00×10^8 m/s

w is in nm (1×10^-9m) and f in hertz (1/seconds)

 

3.00×10^8m/s=600nm(1×10^-9nm/1nm)(f)

5×10^16s=f

f=2×10^-17 hertz

Mixture Examples
Hardwater, soft water, supermarket salt, drugstore hydrogen peroxide

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