Topic 08 introduction
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This document provides an introduction to acids and bases, including: 1) How acids and bases are defined according to the Arrhenius, Bronsted-Lowry, and Lewis theories. Acids donate protons while bases accept protons. 2) Examples of strong acids like HCl and weak acids like acetic acid. Strong acids fully dissociate in water while weak acids only partially dissociate. 3) The pH scale measures hydrogen ion concentration from 0-14, with lower values being more acidic and higher more basic. Neutral solutions have a pH of 7.
![In aqueous solutions, a proportion of the water
molecules dissociate;
The ions formed are H+ or positively charged
hydrogen ions and negatively charged hydroxide ions
(OH-)
Technically
+ -
2 H2O(l) H3O (aq) + OH (aq)
+ − -14
Equilibrium Constant Kw = [H ][OH ] = 1 x 10](https://image.slidesharecdn.com/topic08-introduction-120905184045-phpapp02/85/Topic-08-introduction-2-320.jpg)
![ Some chemical compounds contribute additional H+
to make the solution more acidic. Other compounds
remove H+ ions.
A compound that increases [H+] is called an acid
Examples: HCl, H2SO4, HNO3, CH3COOH](https://image.slidesharecdn.com/topic08-introduction-120905184045-phpapp02/85/Topic-08-introduction-3-320.jpg)
![Strong Acid
example HCl
+ -
HCl(aq) H (aq) + Cl (aq)
[H+ ][Cl- ]
k= >> 1
[HCl]
• completely dissociated
• pH of 0.1 M soln = 1
• strong electrolyte
• reacts vigorously
• note simplified “net ionic”
equation](https://image.slidesharecdn.com/topic08-introduction-120905184045-phpapp02/85/Topic-08-introduction-22-320.jpg)
![Weak Acid
example CH3COOH
+ -
CH3COOH (aq) H (aq) + CH3COO (aq)
[H+ ][CH3COO- ]
k= << 1
[CH3COOH]
• partially dissociated
• pH of 0.1 M soln = 2.9
• weak electrolyte
• reacts slowly](https://image.slidesharecdn.com/topic08-introduction-120905184045-phpapp02/85/Topic-08-introduction-23-320.jpg)
![What is the pH scale?
pH is a measurement of hydrogen ion concentration
It tells you how acidic or basic (or alkaline) something is
Ranges from 0 (most acidic) to 14 (most basic)
pH log[ H ]](https://image.slidesharecdn.com/topic08-introduction-120905184045-phpapp02/85/Topic-08-introduction-24-320.jpg)
Topic 08 introduction
- 1. IB Chemistry Power Points Topic 08 Acids and Bases www.pedagogics.ca Introduction to Acids and Bases
- 2. In aqueous solutions, a proportion of the water molecules dissociate; The ions formed are H+ or positively charged hydrogen ions and negatively charged hydroxide ions (OH-) Technically + - 2 H2O(l) H3O (aq) + OH (aq) + − -14 Equilibrium Constant Kw = [H ][OH ] = 1 x 10
- 3. Some chemical compounds contribute additional H+ to make the solution more acidic. Other compounds remove H+ ions. A compound that increases [H+] is called an acid Examples: HCl, H2SO4, HNO3, CH3COOH
- 4. A compound that removes H+ ions from an aqueous solution is called a base. Often this is done by adding OH- ions for example NaOH, KOH, Ca(OH)2. Soluble bases are called alkalis.
- 5. Types of Neutralization Reactions With hydroxides acid + base water + a salt HCl + NaOH H2O + NaCl (aq) • With metal oxides acid + base water + a salt 2 HCl + Cu2O H2O + CuCl2 (aq) • With ammonia acid + base a salt HCl + NH3 NH4Cl (aq)
- 6. The base is under assault!
- 7. Three theories of acids Arrhenius (most common) Bronsted-Lowry Lewis
- 8. Arrhenius (most common): + an acid dissociates to yield H - and a base dissociates to yield OH Hydrochloric acid + - H + Cl Sodium hydroxide + - Na + OH
- 9. Bronsted-Lowry + an acid is a proton (H ) donor and a base is a proton acceptor
- 11. Lewis: An acid is an electron pair acceptor Lewis Acid Lewis Base and a base is an electron pair donor A dative covalent bond is formed
- 12. This is a common example that is not an obvious acid/base rxn Boron trifluoride acts as a Lewis Acid. The boron has only 6 electron in valence shell so the lone pair of electrons forms a dative bond and fills up the valence shell of the boron
- 13. Indicators Acids and bases are substances with specific physical and chemical properties. We can determine if substances are acidic or basic by testing their reaction with indicators.
- 14. Indicators are organic substances that change color in the presence of an acid or a base. Some common indicators in acid in base Litmus red blue Phenolphthalein colorless pink Methyl orange red yellow
- 16. Reactions of acids – examples to know React with active metals (above copper in reactivity series) 2 HCl + Ca CaCl2 + H2 Reaction with carbonates H2SO4 + Na2CO3 Na2SO4 + CO2 + H2O Reaction with bicarbonates HNO3 + NaHCO3 NaNO3 + CO2 + H2O
- 17. Acid/base properties of Period 3 oxides (topic 3) Metal oxides Na2O and MgO react with water to form hydroxides (basic solutions) Na2O + H2O 2 NaOH (aq) Aluminum oxide is amphoteric (will react as a base with an acid or vice versa) Al2O3 + 6 HCl 2 AlCl3 + 3 H2O Other period 3 oxides (non-metal S, P, Cl oxides) react with water to form acidic solutions SO3 + H2O H2SO4 (aq) see page 15 in study guide
- 18. Acid/base properties of Period 3 chlorides (topic 13) Chlorides across Period 3 become more acidic across the period NaCl (aq) is neutral MgCl2 (aq) is weakly acidic Chlorides of Al, Si, P, S and Cl2 react with water to produce HCl (aq) solutions see Study guide page 16
- 19. Strong Acids vs Weak Acids The strength of an acid or base depends on how easily it dissociates in water. The dissociation of an acid or base is an equilibrium. HA(aq) H+(aq) + A-(aq) BOH(aq) B+(aq) + OH-(aq) Strong acids or bases dissociate (ionize) easily – the equilibrium favors the ionic products : kc >> 1
- 20. Strong vs Weak How to tell Strong acids and bases are mostly ionized and therefore solutions are good electrolytes (high conductivity). The pH of the solution can also be measured.
- 21. Strong vs Weak When the strength of an acid or base is discussed, it is very important NOT to confuse “strength” with “concentration” 3 A 5M acid solution contains 5 mol of acid per dm but its strength is determined by how much of that acid is ionized. Strong acids : HCl, H2SO4, HNO3 (mono vs diprotic) Strong bases : NaOH, KOH, Ba(OH) 2 Weak acids: CH3COOH, H2CO3, carbonic acid CO2(aq) Weak bases: NH3, ethylamine CH3CH2NH2
- 22. Strong Acid example HCl + - HCl(aq) H (aq) + Cl (aq) [H+ ][Cl- ] k= >> 1 [HCl] • completely dissociated • pH of 0.1 M soln = 1 • strong electrolyte • reacts vigorously • note simplified “net ionic” equation
- 23. Weak Acid example CH3COOH + - CH3COOH (aq) H (aq) + CH3COO (aq) [H+ ][CH3COO- ] k= << 1 [CH3COOH] • partially dissociated • pH of 0.1 M soln = 2.9 • weak electrolyte • reacts slowly
- 24. What is the pH scale? pH is a measurement of hydrogen ion concentration It tells you how acidic or basic (or alkaline) something is Ranges from 0 (most acidic) to 14 (most basic) pH log[ H ]
- 25. How does scale work? The scale is logarithmic. As you go up or down, the concentration is changed by a power of ten Example pH 3 is 100 times more concentrated than pH 5 neutral pH 10 is 100 times less concentrated than pH 8