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Transcript
Pure water does not conduct electricity! Def: substances that, when dissolved in water (aqueous solution), conduct an electric current. Therefore, an electrolytic solution allows electricity to flow. The electrical conductivity of a solution is a measure of its ability to allow an electric current to flow through it. When an electrolyte is dissolved in water, it separates into two ions of opposite charges (positive and negative). This is a physical change. 3 conditions must be met in order for an electric current to flow: 1. Electric charges (ions) must be present ions are found in ionic compounds 2. These charges must be mobile when dissolved in water, the ions are pulled apart and are free to conduct electricity 3. The charges must move in a particular direction the electrodes on the electrical conductivity meter direct the charges Ionic compounds!!!! When an ionic compound is placed in water, the ions dissociate. This means that they separate. The solution will now be filled with ions. Def: A solution that contains an electrolyte (hence, that conduct electricity!) Applications: batteries! solid aqueous • When NaCl dissolves in water, sodium and chlorine ions are produced. • A dissociation equation must be balanced (a subscript on the reactant side becomes a coefficient on the product side.) • The charges on the ions must be present. (This is determined by the periodic table) • Subscripts must be written showing the state of the compound or ion. H2O C12H22O11(s) C12H22O11(aq) When dissolved in water, no ions are produced! For example: when sugar is dissolved in water, the molecules remain intact, although they become detached! Positive ions Negative ions negative electrode (cathode) positive electrode (anode) Acids Bases Salts The following are all acids: HCl, H2SO4, HBr, H2S What are some properties of these compounds? • • • • Turn blue litmus paper red. Conduct electricity (electrolytic!) React with metals Sour in taste (but never taste an unknown acid!!) What ions are produced when these acids are dissolved in water? HCl →H+1 + Cl-1 H2SO4 →2H+1 + SO4-2 Acids produce hydrogen ions HBr → H+1 + Br-1 in solution. H2S → 2H+1 + S-2 CH3COOH → H+1 + CH3COO-1 Acids always contain a “H” in the formula. They may also end with “COOH” (exception!) Combinations of C’s and H’s only are not acids. They are hydrocarbons (CH4 and C3H8 ). NH3 is also an exception: it is a base. Bases The following are all bases: NaOH, Mg(OH)2,KOH What are some properties of these compounds? • • • • • Turn red litmus paper blue. Conduct electricity (electrolytic!) Do not react with metals Bitter Slippery to the touch Electrolytic Dissociation What ions are produced when these bases are dissolved in water? Bases produce NaOH →Na+1 + OH-1 Mg(OH)2→Mg+2 + 2OH-1 hydroxide ions in solution. +1 -1 KOH → K + OH NH3 + H20 → NH4+ + OH-1 (exception!) Bases contain “OH” in their formula. A substance produced by the chemical bonding of a metallic ion and nonmetallic ion (other than H+ and OH- ) Ionic compounds (NaCl, MgBr2 , CaSO4) What are some properties of these compounds? • Do not affect litmus paper (neutral!) • Conduct electricity • Do not react with metals 1. 2. 3. 4. 5. 6. 7. 8. 9. NaOH HClO4 CsOH HI HBr HNO3 MgCl2 Sr(OH)2 H2SO4 10.CH3COOH 11.Ba(OH) 2 12.CH4 13.MgSO4 14.Ca(OH)2 15.HNO2 16.K3P 17.HSO418.KOH The pH of a solution is actually an indication of the concentration of H+ ions in that solution. pH means the “power of Hydrogen” Acids release hydrogen ions in solution (water). The water already contains a mixture of hydrogen and hydroxide ions. H2O →2H+1 + OHTherefore in an acidic solution there will be both hydrogen and hydroxide ions. However there will be more hydrogen ions. The pH of acids is less than 7. Bases release hydroxide ions in solution (water). The water already contains a mixture of hydrogen and hydroxide ions. H2O →2H+1 + OHTherefore in a basic solution there will be both hydrogen and hydroxide ions. However there will be more hydroxide ions. The pH of bases is greater than 7 pH = -log[H+] [H+] is the concentration of hydrogen ions On the pH scale, a difference of 1 unit is equivalent to 10 fold difference in acidity! Ex: a solution with a pH of 3 is 10 times more acidic than a solution with a pH of 4! Each unit on the scale represents a factor of 10. A substance with a pH of 9 is 10x10x10x10 more basic than a substance with a pH of 5. 9-5=4 104 = 10x10x10x10 = 10 000 A substance with a pH of 2 is 10x10x10x10x10 more acidic than a substance with a pH of 7. 7-2=5 105 = 10x10x10x10x10 = 100 000 Makes sense?