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Chemestry test 1 notes

by: rebecca goodrich

Chemestry test 1 notes CH 101

rebecca goodrich

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These notes will cover the first exam material
General Chemistry
Paul Rupar
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This 9 page Bundle was uploaded by rebecca goodrich on Thursday February 4, 2016. The Bundle belongs to CH 101 at University of Alabama - Tuscaloosa taught by Paul Rupar in Fall 2015. Since its upload, it has received 24 views. For similar materials see General Chemistry in Chemistry at University of Alabama - Tuscaloosa.


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Date Created: 02/04/16
Law of definite proportions- ratio of mass and quantity will always be the same Ex. 40 g of CO2 is made up of 12 g of carbon. How much oxygen is present? What is the ratio of oxygen to carbon. 40g= total mass 40 g-12 g carbon leaves 28 g oxygen 28 O/ 12 g C = 7:3 John Dalton (1766-1844) Elements are made up of atoms All atoms of an element are the same An atom cannot be created or destroyed Compounds are made of atoms in whole number ratios During a reaction atoms separate and recombine Charges Positive and negative charges (opposite attract), Like charges repel JJ Thomson and the cathode Ray Tube - Glass tube containing metal electrodes from which almost all the air has been evacuated - When connected to a high voltage power supply a glowing area is seen emanating from the cathode - The beam is deflected by external charges and magnets - The cathode rays are made of tiny particles o Negatively charged particles because the were deflected towards the positive plate - Every material contains these particles - Calculated the mass charge ratio of these particles o Charge mass ratio= 1.76*10^9 C.g - The charge was the same as hydrogen ion - If the particle has the same amount of charge as a hydrogen ion then the mass has almost 2000x smaller than hydrogen atoms - Particles are pieces of atoms / a part of atoms - Thomson “discovered” the electron Mulligan- oil drop experiment - Used to determine what the charge of an electron was - Small drops of oil were suspended within a chamber - As the drops of oil fell through the air they were negatively charged by ionizing radiation - Milikan applied an electric field to stop the oil drops from falling - By knowing the mass of the oil drops and the strength of the electric Field, milikan could measure the amount of charge on the drops - He calculated the mass of the oil drops through the assumption that the drops were perfect spheres and therefore the volume is 4/3 pi r^3 - The charge of each drop was always a multiple of -1.60 *10^- 19 C - The charge of e- - Charge always comes in well defined packs - Quantification of physics Found the mass of the electron was 9 *10^-28 g Electrons Electrons are tiny negatively charged particles All atoms are made from electrons The electron has a charge of -1.6*10^-19 C The electron has a mass of 9.1*10^-28g The cathode rays are made of streams of Electrons Review Normal matter is not charged and atoms are not charged Normal matter contains small particles called electrons Why are atoms not negatively chared? - there must be positively charged particles countering the reaction Plum Pudding Model of the Atom- JJ Thomson - There is a positively charged sphere surrounded - First model of the atom to suggest physical parts - Atoms have inner structure Background- - Alpha particles are positively charged particles emitted by dsome radioactive materials o 8000 times heavier than e- Rutherford gold foil Experiment - Rutherford shot alpha particles through gold foil and studied the reaction o A few alpha particles are deflected and others would go through o 98% of the alpha particles went strait through o 2% were deflected at large angles o 0.005% bounced of - Conclusions- Most alpha particles travel though because atoms and matter are empty space o A few of the alpha particles deflect/ bounce o Therefore there must be something very small, very dense, that is positively charged o The atom contains a dense center called the nucleus o The center of the atom o The nucleus is 10^11 times smaller than the atom o Most of the mass of the atom is in the nucleus o The nucleus is positively charged – balancing the electrons o The electrons are in the empty space surrounding the nucleus o He concluded that the nucleus is made of protons o The protons are positively charged o The charges of protons are equal and opposite to that of electrons Atomic Mass A. Many elements have multiple, stable isotopes B. The ratio of diferent isotopes within a sample is constant a. Ex. Chlorine: has 2 common isotopes 35 cl and 37 cl i. CL is 75.77% abundant, 37 CL is 24.33 abundant ii. CL 35- has 17 pt, because it has 17 on periodic table, 18 neutrons because 35-117 C. We calculate the average of the isotopes to determine the atomic mass of an element a. Formula for atomic mass= the sum of (fractional abundance of isotope)n * (mass of isotope)n b. Ex. The exact mass of 35 Cl is 34.97 anu and the exact mass of 37 CL is 36.67 amu. What is the atomic Mass of Chlorine? i. Atomic Mass = (.7577)(34.97)+ (.2433)(36.67)= 35.42 amu Mass Spectrometry - There are many diferent ways for a scientist to measure the mass of an isotope - A mass spectromenter can measure the mass of atoms and molecules - A mass spectrometer works by moving ions past magnets and measuring how much the ions are deflected by the magnets - Lighter ions are deflected more by the magnets o Heavier ions are deflected less - A mass spectrum is a graph that gives the relative mass and relative abundance of each particle - Releative mas of the particle is plotted on the x axis - Releative abundance of the particles is plotted on the y axis 3 signals= 35 cl-35 cl, 35 cl-37 cl, 37 cl-37cl why use mass spectrometry - TO determine isotopic ratio - Measuring the mass of molecules o Can be applied to proteins - Commonly used in foresnsic analysis - Commonly used in medical diagnostics CH 2 Measurement: A quanitative observation - every measurement has a number and a unit - the unit is a comparison to an agreed standard The units are not arbitrary; but are based on a real object or on a fundamental property - kg- was based as a blob of pt-Ir alloy sitting in a vault in France – platinum and iron o 1 lb= 0.4535 kg - - m= distance that light travels in 1/ 299792458 sec certainty and uncertainty - in a scientific measurement, every digit written ins certain except for the last digit - The last digit is estimated, and unless stated otherwise, has an uncertainty of +- 1 - Most measurements have an uncertainty With liquid measurements, measurfe from the bottom of the meniscus In a measurement, all non place holding numbers are significant All non-zero numbers are significant- 2.345 (4 sig figs) All interior zeros are significant- 2304.03 (6 sig figs) Leading zeros are not significant- 0.0034 (2 sig figs) Trailing zeros may or may not be significant -zero after a decimal pt=always significant-4.00= 3sig figs Trailing zeros before a decimal pt are significant- 100.3= 4 sig Trailing zeros before an implied decimal point are ambiguous - 5400= ??? sig figs Exact numbers Some numbers and measurements are exact. Exact numbers have an unlimited number of significant figures Significant figure rules When multiplying and dividing the number of significant figures is the same as that of the lowest number - When adding and subtracting the result has the same number of decimal places as the number with the lowest number of decimal places - Rounding When rounding- 0-4 round down Drop all digits after the last sig fig and leave the last sig fig alone - add insignificant zeroes to keep the value if necessary 5-9 round up - drop all digits after the last sig fig and increase the last sig fig b one - add insignificant zeroes to keep the values if necessary to avoid accumulating extra error from rounding, round only at the end SI – kilometer, meter Volume 1 liter (L) = 1000 milliliters (mL) 3 1 liter (L) = 1000 cubic centimeters (cm ) 1 liter (L) = 1.057 quarts (qt) 1 U.S. gallon = 3.785 liters (L) (gal) Temperature Celsius= freeze at 0 (32 F), boils at 100 (212 F) pleasant day 22C (77F) Coldest possible temperature= absolute zero= -273 C= 0 K C=F-32/1.8 F=1.8C+32 derived units- a combination of other units velocity is a combination a combination of distance and time volume is a measure of space units for volume derive from cubed lengths cubic inches more common units of volume include gallons quarts liters although cubed is not used these are still cubed units si unit of volume= m^3 other common uits of vol= L= 1000 1ml=1cm^3 1ml H2o=1g Density Ratio of mass to volume= m/vol= g/cm^3 Energy of matter All matter pposses energy Energy is classified as kinetic or potential energy Energy can be converted from one form to another When matter undergoes a chemical or physical change the amount of energy in the matter changes as well Kinetic energy= energy of motion Like cars moving Movement of molecules, atoms, electrons, etc Potential energy is energy that is stored in the matter Composition of the matter and its position relative to other things Spontaneous poccesses Materials that have high potential energy are less stable Processes in nature tend to occur spontaneously to lower potential energy Changes in energy An object which has les potential energy at the end of the process has lost energy Energy is never created or destroyed Energy is the ability to do work THe mole A mole of something= 6.02*10^23 somethings= avagadro’s number - why= the mass of 1 mol of a pure compound is numerically equal to its amu mass in grams How many atoms in moles = number of moles times 6.02*10^23 CH 3 Why we need to know about light People use light to probe matter The interaction of light with matter tells us a lot about the nature of molecules We need to be able to describe light if we want to describe matter Waves and structures The world of chemistry runs on quantum mechanics Everything at the molecular scale behaves as a wave A wave can be measured using 3 diferent parameters: the amplitude (height of wave; Wavelength- represented by the symbol lambda, distance from one crest t the next Frequency- the number of waves that pass a point in a given period of time Measured in hertz (or cycles) inverse sec= s^-1= weird v Inverse relationship between frequency and wavelentgth Frequency = velocity/wavelength The nature of light Light is a form of electromagnetic radiation All electromagnetic waves move through space at the same constant speed -3.00*10^8 m/s in a vacuum= the speed of light= c bnbnbnb nnn nn n m since the speed of light is constant , if we know the wavelength we can find the frequency and visa verss7890-= Photons according to Einstein The smallest chunk of light is called a photon or quantum of light The energy of each photon is determined by frequency E=hv H= planck’s constant= 6.626*10^-34 Js R= freq Color = the color of light is determined by its wavelength White light is a mixture of all the colors Visible light comprises only a small fraction of all the wavelenths of light called the- electromagnetic spectrum E= hv Short wavelength (high freq) light is high energy Long wavelength (low frequency) is low energy Very high energy electromagnetic radiation= short freq = can be damaging Ionizing radiation The photoelectric efect It was observed that many metals emit electrons when a light shines on their surface Due to the transfer of photon E to e- Only works with high energy photons Doesn’t work with low energy photons


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