1 Properties of Acids Solutions of acids have a sour taste Don’t taste them in the lab !!! They change the colors of many indicators Acids turn blue litmus to red Acids turn bromothymol blue from blue to yellow They react with metals to generate hydrogen gas, H 2
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Properties of Acids - Texas A&M University · Properties of Acids ... Properties of Bases ... There are four acid-base reaction combinations that are possible: Strong acids – strong
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Properties of Acids
Solutions of acids have a sour taste
Don’t taste them in the lab !!!
They change the colors of many indicatorsAcids turn blue litmus to redAcids turn bromothymol blue from blue to yellow
They react with metals to generate hydrogen gas, H2
They react with metal oxides forming the salt of the metal and water
CaO + 2HCl → CaCl2 + H2O
They react with metal hydroxides forming the salt of the metal and water
Ca(OH)2 + 2HCl → CaCl2 + 2H2O
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OxidesCompounds of oxygen and another elementThere are two ways to name oxides
Based on the oxidation number of the elementLi2O – lithium oxideBaO – barium oxideFeO – iron(II) oxideFe2O3 – iron(III) oxideBased on the number of atoms of each elementLi2O – dilithium oxideBaO – barium oxideFeO – iron oxideFe2O3 – diiron trioxide
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Example 1Name the following compounds:
BeO, Al2O3, Cu2O, OsO4, Cr2O3, CrO3
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Example 2Write formulas for the following compounds:
Example 7Write total and net ionic equations for the reaction between cobalt (III) hydroxide and hydrofluoric acid
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Example 8Write total and net ionic equations for the reaction between aluminum hydroxide and diluted sulfuric acid
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Properties of Acids - SummarySolutions of acids have a sour tasteThey change the colors of many indicatorsThey react with metals to generate hydrogen gas, H2
They react with metal oxides forming the salt of the metal and waterThey react with metal hydroxides forming the salt of the metal and waterAqueous solutions of acids conduct an electric current
Polyprotic acids ionize in two or three steps:H2SO4(aq) + H2O(l) → H3O+(aq) + HSO4
–(aq)HSO4
–(aq) + H2O(l) → H3O+(aq) + SO42–(aq)
The first step in the ionization of a polyproticacids always occur to a greater extent than the second or the third step
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Example 9Write sequence of reactions that takes place upon ionization of phosphoric acid
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Structure of AcidsStructures of binary acids usually are obvious
In most ternary acids the central atom is surrounded by oxygen atoms and then hydrogen atoms are connected to oxygen atoms
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Strengths of Binary AcidsThe strength of an acid reflects the ease of removing a proton from that acid
The H–X bond strength in hydrohalic acids:HF >> HCl > HBr > HI
Acid strength has the reverse trend:HF << HCl < HBr < HI
The same trend applies to the binary acids formed by the VIA elementsBond strength order:
H2O >> H2S > H2Se > H2TeAcid strength has the reverse trend:
H2O << H2S < H2Se < H2Te
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Strengths of Ternary AcidsIn most ternary acids the proton to be removed is bound to an oxygen atomTherefore, the strength of the acid depends on the strength of the O–H bond
HClO HClO2 HClO3 HClO4
Red – more negative (higher electron density)Blue – more positive (lower electron density)
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Strengths of Ternary AcidsTernary acid strength usually increases with:
an increasing oxidation state of the central atom for the acids of the same elementan increasing electronegativity of the central atom for the acids containing elements from the same group in the same oxidation state
ExamplesWhich acid in each pair is stronger:
HNO2 or HNO3?
H2SO4 or H2SO3?
H2SeO3 or H2SO3?
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Strengths of Ternary AcidsIt is important to remember that the comparison of acid strengths can be carried out only for the acids with similar structuresFor example, ternary acids of phosphorus represent an important exception
H3PO2 H3PO3 H3PO4
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The Preparation of AcidsThe binary acids are prepared by reacting the nonmetallic element with H2:
H2(g) + Cl2(g) → 2HCl(g)
Volatile acids, ones with low boiling points, are prepared by reacting salts with a nonvolatile acid like sulfuric or phosphoric:NaF(s) + H2SO4(conc.) → NaHSO4(s) + HF(g)NaCl(s) + H2SO4(conc.) → NaHSO4(s) + HCl(g)
We must use phosphoric acid to prepare HBr or HI:NaBr(s) + H3PO4(conc.) → NaH2PO4(s) + HBr(g)NaI(s) + H3PO4(conc.) → NaH2PO4(s) + HI(g)
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The Preparation of AcidsTernary acids are made by reacting nonmetal oxides (acid anhydrides) with water: