Chemistry notes

• empirical formula- the formula of a compound that express the smallest whole-number ratio of the atoms present 
• molecular formula- the actual formula of a compound- the one that gives the composition of the molecules that are present 
• steps for determining the empirical  formula of a compound 
• step 1: obtain the mass of each element present (in grams) 
• step 2 determine the number of moles of each type of atom
• step 3 divide the number of moles of each element by the smallest number of moles to convert the smallest number to 1. If all of the numbers so obtained are integers ( whole numbers), they are the subscripts in the empirical formula. If one or more of these numbers are not integers, go on to step 4 
• step 4: multiply the numbers you derived in step 3 by the smallest integer that will convert all of them to whole numbers. This set of whole numbers represents the subscripts in the empirical formula. 
•  calculating PH 
• step 1 [H+] 
• press the log key press the +/- key 
• PH = -log [H+]
• PH + pOH = 14 
• steps for calculating [ H+]
• enter PH change the sign of the pH by using the +/- key 
• Take the inverse log of -pH
• a solution is buffered by the presence of a weak acid and its conjugate base 
• intermolcecular forces- forces that occur between molecules 
•  a dipole-dipole attraction: Molecules with dipole moments can attract each other by lining so that the positive and negative ends are close to each other
• London dispersion forces- the forces that exist among noble gas atoms and non polar molecules 
• 0 degrees Celsius is normal freezing point 
• 1 atm is normal pressure 
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