Basic Chemistry IX. Chemical calculations without calculator. Vladimíra Kvasnicová. Neutralization: acid + base salt + water

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1 Neutralization: acid + base salt + water non-stoichiometric neutralization: acid or base in excess Basic Chemistry IX Vladimíra Kvasnicová strong acid + strong base Calculate ph of a solution prepared by mixing 20 ml of 0,01 M sulfuric acid with 20 ml of 0,01 M sodium hydroxide. acid in excess acidic solution (ph = 2,3) weak acid + strong base Calculate ph of a solution prepared by mixing 100 ml of 0,1 M acetic acid (pk = 4,76) with 50 ml of 0,1 M sodium hydroxide. acid in excess buffer solution (ph = 4,76) prepare 200 ml of a 0.5 M solution? How many millilitres of a stock solution of glycine (100 mg/l) and how many millilitres of water do we need to prepare 25 ml of a glycine solution at a concentration of 4 mg/l? Calculate the ph of a M solution of Ba(OH) 2. What is the resulting ph of a solution created by mixing 10 ml of a 0.02 M solution of a weak acid (K A = 10-4 ) with 10 ml of a 0.01 M solution of NaOH? prepare 200 ml of a 0.5 M solution? [18 g] How many millilitres of a stock solution of glycine (100 mg/l) and how many millilitres of water do we need to prepare 25 ml of a glycine solution at a concentration of 4 mg/l? [1 ml / 24 ml] Calculate the ph of a M solution of Ba(OH) 2. [12] What is the resulting ph of a solution created by mixing 10 ml of a 0.02 M solution of a weak acid (K A = 10-4 ) with 10 ml of a 0.01 M solution of NaOH? [4]

2 How many grams of sodium hydroxide (Mr 40) do we need to prepare 250 ml of a 0.2 M solution? How many millilitres of a stock solution of sucrose (0.1 mol/l) and how many millilitres of water do we need to prepare 100 ml of a sucrose solution at a concentration of 5 mmol/l? sulphuric acid of ph 3? What is the ph of a 1 mmol/l solution of a weak monoprotic base (K B 10-4 )? How many grams of sodium hydroxide (Mr 40) do we need to prepare 250 ml of a 0.2 M solution? [2 g] How many millilitres of a stock solution of sucrose (0.1 mol/l) and how many millilitres of water do we need to prepare 100 ml of a sucrose solution at a concentration of 5 mmol/l? [5 ml / 95 ml] sulphuric acid of ph 3? [0,0005 mol/l] What is the ph of a 1 mmol/l solution of a weak monoprotic base (K B 10-4 )? [10,5] prepare 200 ml of a 25 % solution with a density of 1.1 g/ml? sodium hydrogenphosphate with an osmolarity of 0.3 osmol/l? Calculate the ph of a 0.05 M solution of sulphuric acid. What is the ph of a 10 mmol/l solution of a weak monoprotic acid (K A = 10-5 )? prepare 200 ml of a 25 % solution with a density of 1.1 g/ml? [55 g] sodium hydrogenphosphate with an osmolarity of 0.3 osmol/l? [0,1 mol/l] Calculate the ph of a 0.05 M solution of sulphuric acid. [1] What is the ph of a 10 mmol/l solution of a weak monoprotic acid (K A = 10-5 )? [3,5]

3 How many grams of sucrose (Mr 342) do we need to prepare 1 litre of 10 % solution with a density of 1.05 g/ml? What is the osmolarity of a 0.2 mol/l solution of sodium hydrogencarbonate? Ba(OH) 2 with ph 12? What is the final ph of a solution created by mixing 50 ml of 0.01 M ammonium hydroxide (pk B = 4,75) with 25 ml of 0.02 M ammonium chloride? How many grams of sucrose (Mr 342) do we need to prepare 1 litre of 10 % solution with a density of 1.05 g/ml? [105 g] What is the osmolarity of a 0.2 mol/l solution of sodium hydrogencarbonate? [0,4 osmol/l] Ba(OH) 2 with ph 12? [0,005 mol/l] What is the final ph of a solution created by mixing 50 ml of 0.01 M ammonium hydroxide (pk B = 4,75) with 25 ml of 0.02 M ammonium chloride? [9,25] strong acids perchloric acid sulfuric acid hydroiodic acid hydrobromic acid hydrochloric acid nitric acid strong bases sodium hydroxide potassium hydroxide barium hydroxide calcium hydroxide magnesium hydroxide weak acids carbonic acid (unstable: H 2 CO 3 CO 2 + H 2 O) sulfurous acid (unstable: H 2 SO 3 SO 2 + H 2 O) hydrofluoric acid hydrosulfuric acid hydrocyanic acid trihydrogenphosphoric acid organic acids weak bases ammonium hydroxide Oxidation-reduction reactions (redox) oxidation = loss of electrons, oxidation number raises (originally: chemical reaction with oxygen) reduction = gain of electrons, oxidation number lowers (originally: loss of oxygen or reaction with hydrogen) 4 Na + O 2 2 Na 2 O or 2 Na + Cl 2 2 NaCl 2 half reactions: Na is oxidized to Na + O 2 is reduced to O 2- or Cl 2 is reduced to Cl - (oxidation number of an atom in an elementary substance is zero)

4 Oxidation-reduction reactions oxidizing agent = species that oxidizes another species; itself is reduced at the same time reducing agent = species that reduces another species; itself is oxidized at the same time 4 Na + O 2 2 Na 2 O or 2 Na + Cl 2 2 NaCl Electrochemical series of elements shows the order in which metals replace one another from their salts electropositive metals will replace hydrogen from acids K-Ca-Na-Mg-Al-Zn-Cd-Fe-Ni-Sn-Pb-H-Cu-Hg-Ag-Pt-Au Fe + CuSO 4 FeSO 4 + Cu Oxidation-reduction reactions Whether a reaction will occur between a given element and a monoatomic ion depends on the relative ease with which the two species gain or lose electrons. the list of elements in order of their ease of losing electrons during reactions in aqueous solutions explains their chemical reactivity with acids: react vigorously with acids (and also with liquid water) to give H 2 react with acids to give H 2 (e.g. Zn + H 2 S ZnS + H 2 ) do not react with acids to give H 2 K-Ca-Na-Mg-Al-Zn-Cd-Fe-Ni-Sn-Pb-H-Cu-Hg-Ag-Pt-Au strongest reducing properties weakest reducing properties strong oxidizing agent Standard redox potentials E weak reducing agent In the Electron Transport Chain (Respiratory Chain) in cells electrons are transfered from NADH (organic molecule) gradually to oxygen which is thus reduced to H 2 O reducing properties oxidizing power increases reducing power increases Gibbs energy G Redox potential E weak oxidizing agent strong reducing agent oxidizing properties Zn + Cu 2+ Zn 2+ + Cu The figure is found at Ed1/Chapter14_13/REDOX_POTENTIALS_ElectronTransportChain_Fig14-21.htm (December 2006)

5 The figure is found at (December 2006)