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Chemistry 40s

Chemistry 40s. Unit 1: reaCTIONS IN AQUEOUS SOLUTIONS. LEARNING OUTCOMES. C11-1-04: Write balanced neutralization reactions between strong acids and bases.

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Chemistry 40s

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  1. Chemistry 40s Unit 1: reaCTIONS IN AQUEOUS SOLUTIONS

  2. LEARNING OUTCOMES • C11-1-04: Write balanced neutralization reactions between strong acids and bases. • C11-1-05: Perform a laboratory to activity to demonstrate the stoichiometry of a neutralization reaction between a strong base and a strong acid. • C11-1-06:Calculate the concentration or volume of an acid or a base from the concentration and volume of an acid or a base required for neutralization. • C11-1-07: Design and test a procedure to determine the identity of a variety of unknown solutions.

  3. DEFINING ACIDS & bases • According to Arrhenius: • Acids and bases must ionize or dissociate in water • Arrhenius Acid – substance that releases hydrogen ions in water • Example 1: Hydrochloric acid • HCl(aq)  H+(aq) + Cl-(aq) • Example 2: Acetic acid • HCH3COOH(aq)  H+(aq) + CH3COOH-(aq) • Usually begin with one or more hydrogen atoms

  4. Defining acids & bases • Arrhenius Base – a substance that releases hydroxide ions (OH-) in water • Example 1: Sodium hydroxide • NaOH(s)  Na+(aq) + Cl–(aq) • Example 2: Aqueous ammonia • NH3(g) + H2O(l)  NH4OH(aq) + OH-(aq) • Many bases, with the exception of ammonia, will contain one or more hydroxide ions

  5. Properties of acids • Taste sour. E.g. lemons (citric acid) and vinegar (acetic acid) • Burn when touching skin. • Neutralize basic solutions. • React with carbonates to produce carbon dioxide gas • Acid + carbonate → salt + water + carbon dioxide gas • Corrosive to metals • Many acids react with active metals to produce hydrogen gas. • Acid + metal → salt + hydrogen gas • Turn litmus red • pH < 7

  6. Common acids – know these • Hydrochloric acid = HCl • Sulfuric acid = H2SO4 • Nitric acid = HNO3 • Acetic acid = HCH3COOH • Carbonic acid = H2CO3 • Nitrous acid = HNO2 • Sulfurous acid =H2SO3 • Phosphoric acid = H3PO4 • Hypochlorous = HClO

  7. Types of acids • Acids can be classified based on the number of hydrogen ions they contain: • Monoprotic Acids e.g. HCl, HNO3, HCH3COOH • Release one proton per molecule of acid dissociated in water • Diprotic Acids e.g. HCO3, H2SO4, H2SO3 • Release two protons per molecule of acid dissociated in water • Triprotic Acids e.g. H3PO4 • Release three protons per molecule of acid dissociated in water

  8. Properties of bases • Taste bitter, similar to soap • Slippery touch • pH > 7 • Caustic, meaning bases degrade animal tissues • Neutralize acids • Turn litmus blue, phenolphthalein pink and bromothymol blue blue

  9. Common bases • Sodium hydroxide = NaOH • Potassium hydroxide = KOH • Magnesium hydroxide = Mg(OH)2 • Calcium hydroxide = Ca(OH)2 • Ammonia = NH3 • Aluminum hydroxide = Al (OH)3

  10. Types of bases • Bases can be classified based on the number of hydroxide ions that they release per molecule of water: • Monohydroxic e.g. NaOH, KOH • Release one OH- ion • Dihydroxic e.g. Mg(OH)2, Ca(OH)2 • Release two OH- ions • Polyhydroxic e.g. Al (OH)3 • Release more than two OH- ions

  11. Neutralization reactions • A neutralization reaction is special double replacement reaction between an acid and a base. • The products of this reaction are water and a salt. • Salt – a compound composed of the negative ion of an acid and the positive ion of the base. • In general, the reaction for a neutralization reaction is given by: • Acid + base  salt + water • Example: Hydrochloric acid and sodium hydroxide • HCl(aq) + NaOH(aq) → NaCl(aq) + HOH(l) • H+ from acid combines with the OH- from the base to form H2O • The leftover anion and cation = salt

  12. Writing Neutralization reactions • Just as with precipitation & dissolution you should be able to write the below equations for each neutralization reaction: • Step 1: Write the formulas for each reactant • e.g. hydrochloric acid = HCl and sodium hydroxide = NaOH • Step 2: Write the balanced molecular equation HCl(aq) + NaOH(aq)→ NaCl(aq) + HOH(l)

  13. Writing neutralization reactions • Step 3: Write the balanced ionic equation • 2 K+(aq) + 2 OH–(aq) + 2 H+(aq) + SO42–(aq) → 2 H2O(l) + 2 K+(aq) + SO42–(aq) • Step 4: Eliminate the spectators and write the balanced net ionic equation • 2 K+(aq) + 2 OH–(aq) + 2 H+(aq) + SO42–(aq) → 2 H2O(l) + 2 K+(aq) + SO42–(aq) • For all neutralization reactions the net ionic equation should be: • H+(aq) + OH–(aq) → H2O(l)

  14. Stoichiometry of neutralization • When an acidic solution is added to a basic solution, we can predict the amount of that acid needed to neutralize the base. • At the point of neutralization, the # of hydrogen ions and hydroxide ions will be equal: • Moles of H+ = Moles of OH- • AND • Moles of H+ = CA x VA • Moles of OH- = CB x VB • Therefore: • CA x VA = CB x VB

  15. Solving neutralization problems • Ex 1. Calculate the concentration of hydrochloric acid, if 25.0 mL is just neutralized by 40.0 mL of a 0.150 mol/L sodium hydroxide solution.

  16. Solving Neutralization problems • Ex 2. What volume of 1.00 mol/L potassium hydroxide is needed to neutralize 750. mL of a 0.500 mol/L nitric acid solution?

  17. Solving neutralization problems • Ex 3. What is the concentration of a sample of magnesium hydroxide, if 225 mL of the base is neutralized by 125 mL of a 0.200 mol/L hydrochloric acid solution?

  18. Solving neutralization problems • Ex 4. Calculate the volume of 0.100 mol/L carbonic acid needed to neutralize 25.0 mL of 0.200 mol/L sodium hydroxide.

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