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Acids bases & salts. Objectives State the Bronsted-Lowry definition of acids and bases Identify the common physical and chemical properties of acids and.

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Presentation on theme: "Acids bases & salts. Objectives State the Bronsted-Lowry definition of acids and bases Identify the common physical and chemical properties of acids and."— Presentation transcript:

1 Acids bases & salts

2 Objectives State the Bronsted-Lowry definition of acids and bases Identify the common physical and chemical properties of acids and bases Explain what dissociation constants indicate about an acid or base Use experimental data to calculate a dissociation constant

3 Properties of acids/bases Taste – acid comes from latin meaning sour or tart/bases are bitter – soap Touch most dilute acids feel like water although they sting on broken skin bases feel smooth, soothing and slippery except in your eyes (soap) Reactions with metal acids react bases do not react

4 Properties continued Electrical conductivity water is poor – HCl is good, NaOH is good both are electrolytes Indicators turn color – acid turns litmus paper from blue to red base turns from red to blue Neutralization reaction between an acid and a base get salt and water (double replacement)

5 Arrhenius definition An acid is a substance that dissociates in water to produce hydrogen ions. A base is a substance that dissociates in water to produce hydroxide ions A salt is an ionic compound formed from any cation other that H + and any anion other than OH - or O -2

6 Arrhenius continued Acids react with metals to produce H 2 gas Mg +2H + -> Mg +2 + H 2 oxidation reduction reaction

7 Bronsted – Lowry definitions An acid is any substance that can donate H + ions A base is any substance that can accept H + ions a Bronsted-Lowry acid is a proton donor and a base is a proton acceptor

8 Hydronium Ion H+ is strongly attracted to the electrons of surrounding water molecules H + + H 2 O -> H 3 O + More correct HCl + H 2 O -> H 3 O + + Cl - In this case HCl is the Bronsted-Lowry acid and water is the base We still describe a solution of HCl as acidic!

9 NH 3 + H 2 O -> NH OH - Ammonia is the H + acceptor water is the H + donor (acid) Amphoteric a substance that can act as either an acid or a base

10 Conjugate Acid-Base Pairs NH 3 + H 2 O  NH OH - In 1 direction water is the acid in the reverse reaction it is the base. These cmpds become conjugate acids and conjugate bases when HCl loses an H+ ion to become its conjugate base Cl - when the conjugate base of water is the hydroxide ion OH - When ammonia gains H + to become its conjugate acid NH 4 + and the conjugate acid of OH - is H 2 O

11 Conjugate pairs A pair of compounds that differ by only one H + ion such as H 2 O and OH - or NH 3 and NH 4 + are called conjugate acid base pairs NH 3 + H 2 O  NH OH - Base acid conj. Acid conj. base

12 Determining the strengths of acids and bases A strong acid HCl readily transfers hydrogen ions to water to form H 3 O + If you place 1M of HCl in 1 liter of water you would form 1 M H 3 O + ions and 1 M Cl - ions

13 weak acids A weak acid does not readily transfer H+ ions 1 mole of acetic acid in 1 liter of water only.4% of the acetic acid molecules would form H 3 O + and C 2 H 3 O 2 -. Which means that 99.6% of the acetic acid molecules do not dissociate.

14 To show a strong acid from a weak acid use arrows HCl + H 2 O  H 3 O + + Cl - HC 2 H 3 O 2 + H 2 O H 3 O + + C 2 H 3 O 2 -

15 Strong and Weak Bases The most widely used commercial base is CaO. When CaO is dissolved in water the O -2 ions react completely with H 2 O to form OH - ions. O -2 + H 2 O  2OH - use a single arrow

16 Strength of conjugate acid – base pairs The stronger the acid the weaker its conjugate base. The stronger the base the weaker its conjugate acid.

17 The acid dissociation constant K a Weak acid HA HA + H 2 O H 3 O + + A - K eq = For a 1 M solution of a typical weak acid may be only.007% of the water molecules react. Move the water to the left side of the equation The higher the K a the more the reaction goes to the right. The greater the K a the stronger the acid Weak acids have a K a less than 1

18 Diprotic acids 2 step dissociation

19 Base dissociation constant K b The base dissociation constant is a measure of the strength of a base Do calculations of dissociation constants

20 Objectives Explain what most acidic hydrogen atoms have in common Explain what most bases have in common Describe how acids are named

21 Naming and identifying acids and bases 1 st all H’s are not acidic CH 4 As a rule an acidic hydrogen already has a slight positive charge while is it part of a molecule. (It is in the positive side of a polar covalent bond) Usually bonded with O, N, or a halogen

22 3 types of acids Binary acids - H and 1 other element usually 6A or 7A Strong HCl, HBr, and HI Weak HF, H 2 S and H 2 Se Oxy acids contain H, O and 1 other element H 2 SO 4, HNO 3 and H 3 PO 4 Carboxylic Acid – organic acids COOH group Acetic acid HC 2 H 3 O 2 vinegar

23 Bases A Bronsted-Lowry base always contains an unshared pair of electrons NH 3 attracts H + Anions: remember conjugate bases HCl Cl - Weak Cl - Br - I - NO 3 - HSO 4 - CIO 4 - Strong O -2 OH - PO 4 -3 and CO 3 -2 Amines N has an unshared pr. Of electrons

24 Naming Acids and Bases If the name of an anion ends in ide the name of the acid that produces it includes the name of the anion, a hydo prefix Hydrochloric acid – all binary acids If the name of an anion ends in ate use and ic ending Nitric acid, carboxylic acid Anion ends in ite SO 3 -2 sulfite ion H 2 SO 3 sulfurous acid


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