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Reactions in Aqueous Solutions

Reactions in Aqueous Solutions. By: Shivali Gupta, Michelle Sodipo, Sae’Von Springer , Timothee Schlumburger , Anju Shilpa Suresh, Destiney Randolph. Predicting Whether a Reaction will Occur. Formation of a solid Transfer of electrons Formation of water Formation of a gas

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Reactions in Aqueous Solutions

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  1. Reactions in Aqueous Solutions By: Shivali Gupta, Michelle Sodipo, Sae’VonSpringer , TimotheeSchlumburger, AnjuShilpaSuresh, DestineyRandolph

  2. Predicting Whether a Reaction will Occur • Formation of a solid • Transfer of electrons • Formation of water • Formation of a gas If any of these happen, a reaction is likely to take place.

  3. Reactions in Which a Solid Forms • One kind of reaction which results in the formation of a solid is precipitation, which forms a precipitate. • By mixing certain solutions of compounds, a chemical reaction occurs resulting in a solid. • When ionic compounds dissolve in water, the ions separate and float freely in the solution. • We can test this by testing the electrical conductivity of the solutions” • Pure water, with no ions present cannot conduct electricity. • Water with ions present conducts electricity. • This kind of solution is called a “strong electrolyte” Ex. Barium Nitrate because each Ba(NO3)2 compound produces the ions Ba(2+), NO3(1-), and NO3(1-)

  4. By finding these ions, or reactants, we can then proceed to make some educated guesses about the possible products that these ions can form. • To make an educated guess, you must first take each ion, and consider all the possible combinations. • Eliminate all the unlikely combinations, for example, all the combinations that have two cations or two anions.

  5. However, to specify the formation of a solid product, you have to ensure that the combination has opposite charges. • Na(1+) and Cl(1-) => solid • (vs.) Be(2+) and F(1-) => Not a solid

  6. Describing Reactions in Aqueous Solutions • Molecular equation- a chemical equation showing the complete (undissociated) forms of all reactants and products. Ex: K2CrO4(aq) + Ba(NO3)2(aq) BaCrO4(s) + 2KNO3(aq)

  7. Complete Ionic Equation- a chemical equation for a reaction in solution representing all strong electrolytes as ions. 2K+(aq) + CrO4-2(aq) + Ba+2(aq) + 2NO3-(aq) BaCrO4(s) + 2K+(aq) + 2NO3-(aq)

  8. Spectator Ions- an ion present in solution that does not participate in a reaction • Net Ionic equation- a chemical equation for a reaction in solution showing only those components that are directly involved in the reaction. Strong electrolytes are represented as ions. Ex: Ba+2(aq) + CrO4-2(aq) BaCrO4(s)

  9. Acids! Originally associated with citrus fruits Acid = Latin “Acidus” = Sour Mineral Acids, such as sulfuric (H2SO4) & nitric acid (HNO3) found around 1300 Derived from from the treatment of minerals In 1800s, Svante Arrhenius discovered nature of acids

  10. Svante Arrhenius Swedish physics graduate Experiment showed that HCL, HNO3, and H2SO4 behaved as strong electrolytes, because of ionization reactions. Nearly every molecule of acids breaks down into ions when placed in water. Acid = Substance that produces H+ ions (protons) id Acids when it is dissolved in water Strong Acids = Acid that breaks apart to make H+ ions in solutions

  11. Bases Aqueous solution that exhibit basic behavior always contain hydroxide ions Base = Substance that produces hydroxide ions (OH-) in water Strong Base = Substance that breaks apart to form OH- ions in solutions When strong acids and strong bases are mixed, H= and OH-, the chemical change forms water molecules

  12. In Chapter 3, we talked about ionic compounds which are compounds formed in the reaction of a metal and a nonmetal. 2Na(s) + Cl2(g)  2NaCl(s) • Sodium metal is composed of sodium atoms (net charge of zero) with seven protons & electrons • Similarly, the chlorine molecule consist of two uncharged chlorine atoms with seventeen protons & electrons • HOWEVER, in the product (sodium chloride), the sodium and chlorine is presented as Na+ and Cl- respectively Na + Cl Na+ and Cl- One electron is transferred from each sodium atom to each chlorine atom This process coverts neutral atoms to become ions

  13. Na + Cl Na+ and Cl- An electron from sodium is transferred over to Chlorine. Now, sodium’s charge, which was originally zero because of the equal number of electrons and protons, is now positive because it gave away one of it’s electrons. Similarly, Chlorine’s charge, which was also originally zero with a balance of seventeen protons and electrons, is now negative as it receives an extra electron from sodium.

  14. In a nutshell In order to form an ionic bond, it is necessary for the metal(cation) to transfer over one more electrons to the non-metal (anion) This reaction of transferring over electrons is called OXIDATION-REDUCTION REACTION.

  15. In the world around us and even in our bodies, literally millions of chemical reactions are taking place. What causes these chemical reactions?

  16. “Driving Forces” Chemical reactions have four major “driving forces” • Formation of a Solid • Formation of Water • Transfer of Electrons • Formation of a Gas

  17. Formation of a Solid • Precipitation- formation of a solid when tow solutions are mixed • Precipitate- solid formed by mixing two solutions

  18. K2CrO4 (aq) + Ba(NO3)2(aq) BaCrO4(s) +2KNO3(aq) NOTICE in this reaction that the two anions (NO3- and CrO42-) are exchanged. CrO42- was originally associated with K2 and NO3- was originally associated with Ba2+ In the product, NO3- now associates with K2 and CrO42- now associates with Ba2+ In this reaction, associations are REVERSED We call this DOUBLE-DISPLACEMENT REACTION. AB + CD  AD + CB

  19. Formation of Water strong acid + strong base  formation of water H+ (aq) + OH- (aq)  H2O (l) We classify these reactions as ACID-BASE REACTIONS Involves an H+ ion that ends up in the product water

  20. Transfer of Electrons We see this driving force particularly in the “desire” of metal to donate electrons to non metals. 2Li(s) + F2(g)  2LiF(s) Each lithium atom loses one electron to form Li+ ion Each fluorine atom gains one electron to form F- ion Process of electron transfer is called OXIDATION-REDUCTION

  21. Formation of a Gas A reaction in aqueous solution that forms a gas (which escapes as bubbles) is pulled toward the products by this event. 2H+(aq) + CO32-(aq)  CO2(g) + H2O(l) Note that it forms carbon dioxide gas as well as water which illustrates two driving forces. Because this reaction involves H+ ion that ends up in the product water, what type of reaction do we classify this as?

  22. ACID-BASE REACTION

  23. How about this one Zn(s) + 2HCl(aq)  H2(g) + ZnCl2(aq) NOTICE, in the reactants, zinc exists as uncharged atoms, whereas in the product it exists as Zn2+. This can only mean that each Zn atom lost 2 ELECTRONS. So what happened to the electrons? The electrons have been transferred to two H+ ions to form H2 What reaction has taken place?

  24. OXIDATION-REDUCTION REACTION!

  25. BUT WAIT, THERE’S MORE!

  26. Do you recall the double-displacement reaction where associations were reversed? K2CrO4(aq) + Ba(NO3)2(aq) BaCrO4(s) +2KNO3(aq) In double-displacement reaction, TWO anions (NO3- and CrO42-) have been exchanged. So, what does this have to do with this chemical formula? Zn(s) + 2HCl(aq)  H2(g) + ZnCl2(aq) In this chemical formula, ONE anion (Cl-) is being exchanged between H+ and Zn2+ We call this SINGLE-REPLACEMENT REACTION A + BC  B + AC

  27. Other Ways to Classify Reactions • Combustion Reactions • Combustion reactions- a chemical reaction involving oxygen as one of the reactants that produce enough heat so that a flame results. • Ex. Natural Gas reacts with Oxygen CH4 + 2O2 (g) CO2 (g) + 2H2O (g)

  28. Combustion reactions, are a special class of oxidation-reduction reactants • Many combustion reactions may provide heat or electricity for homes or energy for transportation. • Ex. Combustion of Gasoline (used to power cars &trucks) 2C8H18 (l) +25O2 (g) 16CO2 (g) + 18H2O (g)

  29. Synthesis (Combination) Reactions • Synthesis reactions (Combination reaction) – a chemical reaction in which a compound is formed from simpler materials. • Ex. Not involving oxygen 2Na(s) + Cl2 (g) 2NaCl(s) • Ex. Starting with elements 2H2 (g) + O2 (g) 2H2O (l) • Synthesis reactions are another subclass of the oxidation – reduction class of reactions.

  30. Decomposition Reactions • Decomposition reactions – a chemical reaction in which a compound is broken down into simpler compounds or to the component elements. • Ex. Heat • 2HgO(s) 2Hg (l) + O2 • A decomposition reaction, in which a compound is broken down into its elements, is just the opposite of synthesis (combination) reaction in which elements combine to form the compound

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