CHM 104 1st Edition Exam 2 Study Guide Lecture 1 6 Lecture 1 February 11 Introduction to the LeChatlier s Principle How does a reaction react when thrown out of equilibrium forward and backward reaction rates are equal and is put under stress Equilibrium is when the forward and backward reaction rates of a reaction are equal and when it experiences certain stressors it works to bring the reaction back into equilibrium Example Reaction H2 I2 2HI If H2 is added the reaction shifts to the RIGHT because to undo this stress the reaction tries to make more products HI If I2 is removed the reaction shifts to the left to make more reactants and return to equilibrium If HI is removed the reaction will shift to the right to make more of the product to return to equilibrium Example Reaction 2NOCl 2NO Cl2 If the pressure of the system is increased the reaction shifts to the side with FEWER moles Think of this in terms of the PV n RT equation When pressure increases the moles also increase So when the pressure moles of the system is increased in order to return to equilibrium the reaction must shift to the side with the least number of moles In this case the reaction would shift to the LEFT 2 vs 3 moles If the pressure is decreased the opposite effect occurs This will make the reaction shift to the right the side with more moles IF there are the same numbers of moles on both sides then a pressure change will NOT disturb the reaction s equilibrium Lecture 2 February 20 Introduction to Strong and Weak Acids What kind of compounds can be considered an acid What is water considered to be an acid or base What happens when you add water to a strong acid How do we determine pH of an acid What is a strong acid A strong acid is a strong electrolyte that in solution dissociates completely in into its ions Acids are DONORS of the ion H These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Strong acids include HCl HBr HI HClO4 H2SO4 and HNO3 When water is added to a strong acid the products include H 3O and the conjugate base of the strong acid Example Reaction HNO3 H2O H3O NO3 REMEMBER EQUATIONS WITH A STRONG ACID WILL NOT BE IN EQUILIBRIUM What happens when water reacts with itself Can it act as an acid AND base Take a look at this equation H2O H2O H3O OH In this example water acts as an acid and a base because the products include H 3O and OH the main ion of a dissociated base OH is the conjugate base and the H 3O is the conjugate acid This reaction is called autoionization Now this autoionization equation can be used to find the equilibrium constant of water called K w This is determined using the same tactics used to find K c Ka and Kb Kw H3O OH Remember water is not included because it is a liquid The H3O concentration since it is a STRONG acid will have the same H concentration Therefore H OH Kw and will always equal 1 0 10 14 In acid base equilibrium equations the weaker acid base side is favored When neutral H and OH are both 1 0 10 7 M when the H concentration exceeds the OHconcentration the solution is acidic and vice versa When the concentrations for H and OH are given how can we find pH and pOH What s the relationship between pH and pOH pH log H pOH log H pH SCALE 1 Strong Acid 14 Strong Base pH pOH 14 What if the pH or pOH are given and not the concentrations The same equations above will be used You must undo the log to get H 10 pH and OH 10 pOH Example Problem A blood sample has an OH of 2 5 10 7 What is the pH and the H concentration pOH log 2 5 10 7 Poh 6 60 pH pOH 14 14 6 60 pH 7 4 H 10 pH 10 7 4 4 0 10 8 M So we just learned how strong acids act but how do weak acids act A weak acid is an acid that doesn t disassociate completely but only partially The Ka of a weak acid is much smaller than one of a stronger acid and have higher pHs than a stronger acid In strong acids the disassociated ions had the same concentration as the original solution but with weak acids since it is dissociated only partially they will have different concentrations than the initial solution For example 5 M of the weak acid HF will NOT have 5 M of H and 5 M F But with a strong acid like HCl 5M of this solution ALSO means 5 M H and 5 M Cl Lecture 3 February 25 Introduction to Polyprotic Acids What are polyprotic acids How do they act in comparison to a regular monoprotic acid A polytropic acid is an acid that can donate more than one 1 proton of H For example H2SO4 H HSO4 HSO4 H SO4 2 With problems dealing with polytropic diprotic acids two K a values are involved Ka2 is ALWAYS smaller than Ka1 Because of the small Ka value these reactions are favored towards the REACTANTS In these problems TWO ICE TABLES are needed The equilibrium concentrations calculated in the first ICE table are the initial concentrations of the second ICE table Lecture 4 February 27 Introduction to Weak Bases What are weak bases and how do they act in solution Weak bases react with water to produce OH They ARE in equilibrium Must have a lone pair in its Lewis structure in order to accept an H ion Example Reaction NH3 H2O NH4 OH These reactions are very reactant favored For a weaker base there is going to be a STRONGER conjugate acid and vice versa The pH pOH is calculated the same way as a weak acid an ICE table and calculating the equilibrium constants Key concept All bases have a lone pair but not everything with a lone pair will be a base Lecture 5 March 2 Introduction to Salt Hydrolysis Salt Hydrolysis is the reaction of adding water to a salt This salt is the PRODUCT of acid base neutralization The products of strong acid base reaction are water and this salt A salt from a strong base and strong acid however will NOT hydrolyze so the pH would be 7 For example KCl is the salt from the strong acid HCl and the strong base KOH By itself K does not accept pH because it is neither an acid nor a base By itself Cl does not accept pH either because it has no H to donate and it does not act as a base But when a salt from a strong acid and a weak base hydrolyze the pH will be lower When a salt from a …