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Acids-Bases and Indicators Chemistry 1105
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background An extremely large class of reactions Found in Biochemistry – Cleaning products Industrial fabrication foods
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Theory Historically known but not understood Gay-Lussac defined them in 1814 But in terms of each other Svante Arrhenius won the Nobel Prize for his definition the Acids and Base work This is still the one most often used for acids and bases
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Definitions Arrhenius Acid Releases hydrogen ion Produces H 3 O + HNO 3 + H 2 O → H 3 O + + NO 3 - Arrhenius BASE Releases OH ion in water NaOH + H 2 O Na + + OH - + H 2 O
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Strong vs. Weak Strong Acid/Base Completely Dissociates No Equilibrium No Reactants Are Observed After Reaction HNO 3 + H 2 O → H 3 O + + NO 3 - NaOH + H 2 O → Na + + OH - + H 2 O Only Few Strong Acids And Bases
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Strong vs. Weak Weak Acid/Base Partially Dissociates Reaction Is In Equilibrium Products And Reactants Observed HF + H 2 O ↔ H 3 O + + F -
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pH Reference is Water Water is amphoteric- Characteristics of both acid and base H 2 O + H 2 O ↔ H 3 O+ + OH - In Pure Water, [H 3 O+] = 1.0 x 10^(-7) [OH - ] = 1.0 x 10^(-7) pH = -log [H 3 O+] = -log(1.0 x 10^(-7)) = 7 Most water is not 7 Our is between 4-5
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history Brønsted and Lowery in 1923 Showed that an acid or a base could be donors and acceptors with a H present HF + H2O ↔ H3O+ + F- And as in water H 2 O ↔ H+ + OH - Where HO- a Lewis base and H+ the Lewis acid.
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Indicators Complex molecules that absorb light at different wavelengths Acid or a base and it reacts with the compound Changes the wavelength and thus the color
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Indicators Iitmus paper- made from lichens Red, acid, Blue, base Lots of possible indicators and more daily Thymolblue Methyl orange Yamada is a universal indicator Red to orange in acid, green at neutral, and blue to indigo in acid
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Acid Content The number of hydrogen ions available in the acid Sulfuric acid H 2 SO 4 ACID CONCENT =2 HCl = 1 Measured by Titrations
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Titrations Titration is a procedure used to determine the concentration of an acid or base. Neutralization HCl+NaOH NaCl+H 2 O Need to know The initial concentration of the base The initial volume of acid The amount of base that is used to neutralize the acid
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Titration Moles of acid = moles of the base Changes pH starts acidic goes basic At neutralization of strong acid and strong base =7 Neutral. Not always 7, Depends on the acid and the base
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Experimental Procedure Acid and Base In 5 wells 3 drops of X and 3 drops of Y Using litmus paper blue and red record reaction One drop yamada, thymolblue, methy orange pH scale 10 wells add one drop of each of the std solutions1-10 Then add I drop yamada, record color
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pH scale Determine the pH of the X and Y Now test pH using Yamada Nitric acid (0.1 M) Acetic acid (0.1 M) Ammonia hydroxide (0.1 M)
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Titration Use unknown acid from above Add one drop in each of 10 wells Add one drop Yamada to each well number 1 add 1 drop NaOH Well number 2 add 2 drops etc. to ten with 10 drops Now repeat with the other unknown base and titrate with acid
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1) Place 3 drops of solution X Place 3 drops of solution Y 2) Test pH with red and blue litmus paper, Yamada, bromocresol, and thymol blue Indicators. 3)Place 5 drops of each pH solution 1-10 in Separate wells. Add one drop of YAMADA indicator 4)Using the scale determine pH of solutions X and Y. 5) Take 5 drops of 0.1M nitric acid and 5 drops of 0.1M acetic acid and test with Yamada indicator Creating a pH scale 1 2 3 4 5 6 7 8 9 10 NOTE: THE COLORS ARE JUST AN EXAMPLE DO NOT REPRESENT REAL COLORS IN THE EXPERIMENT 1 X Y
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How should it look?
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Titration In 12 different clean wells place: 1 drop of BASE (unknown X or Y) to each wells 1 drop of indicator Titrate with base HCl 0.005M adding 1 drop to well 1 2 drops to well 2 3 drops to well 3 Continue until you find the green neutral color
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Titration Add 0.005M NaOH In 12 different clean wells place: 1 drop of ACID (unknown X or Y) to each wells 1 drop of indicator Titrate with base NaOH 0.005M adding 1 drop to well 1 2 drops to well 2 3 drops to well 3 Continue until you find the green neutral color
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Titration In 12 different clean wells place: 1 drop of ACID (unknown X or Y) to each wells 1 drop of indicator Titrate with base NaOH 0.005M adding 1 drop to well 1 2 drops to well 2 3 drops to well 3 Continue until you find the green neutral color
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Acid and Base Which well is neutralization How many drops Do report (Note: Each drop is 0.05 mls)
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