Unit 7 Reactions in Aqueous Solutions

Types of Chemical Reactions  Precipitate reaction Double Replacement  Acid – Base reaction  Oxidation – Reduction reaction (redox) Combustion reaction Synthesis reaction Decomposition reaction Single Replacement

Signs of a Chemical Reaction  Color change  Change in temperature  Formation of a gas (look for bubbles)  Formation of a precipitate (precipitate is a solid formed when mixing 2 liquids together) Remember !

Precipitate Reaction Reactants are dissolved as ions in solution. They are strong electrolytes. K 2 CrO 4 (aq) + Ba(NO 3 ) 2 (aq)  products 2 K + 1 (aq) + CrO (aq) + Ba + 2 (aq) + 2 NO (aq)  products Problem is to decide what the products are!

Solubility Rules  Soluble means that the product will dissolve in water.  Low solubility means that is insoluble, it will NOT dissolve in water.  The chart lists anions (negative ions) and cations (positive ions)

Formation of a Precipitate: Happens when 2 solutions are mixed, and a solid is formed due to a combination of ions that is not soluble, will not dissolve in H 2 O. 1. Determine the ions present in each solution 2. Using the Solubility of common compounds in water chart, determine which combination of ions has low solubility Low solubility means will precipitate and form a solid 3. Write the balanced ionic equation for the formation of the precipitate. Ba(NO 3 ) 2  Na 2 CrO 4 

Chemical Equations – 3 types to write  Complete Molecular chemical equations show all chemicals as complete formulas. K 2 CrO 4 (aq) + Ba(NO 3 ) 2 (aq)  BaCrO 4 (s) + 2 KNO 3 (aq)  Complete Ionic chemical equations show all chemicals in their actual form. 2K + 1 (aq) +CrO (aq) +Ba + 2 (aq) +2NO (aq)  BaCrO 4(s) +2K 1 (aq) +2NO (aq)  Net Ionic chemical equations show only the chemicals that are directly involved in the reaction. Ba + 2 (aq) + CrO (aq)  BaCrO 4 (s) Spectator ions, those not involved, are not included.

Write all 3 types of chemical reactions for the following combinations. 1. Barium nitrate with sodium chromate 2. Aluminum sulfate with strontium nitrate 3. Cobalt (II) chloride with potassium hydroxide 4. Magnesium chloride with sodium hydroxide 5. Copper (II) chloride with sodium carbonate

Mixture is a substance composed of two or more individual components. The physical properties (such as density, melting point, boiling point) can change. A homogeneous mixture is uniform in composition. A solution is a homogeneous mixture. Example: sugar dissolved in H 2 O A heterogeneous mixture is non-uniform in composition. Example: Sand mixed with gravel There are 3 kinds of solutions a. Gaseous solution: All are homogeneous mixtures. Example: the air b. Solid solution: A solid dissolved in a solid, Alloys. Example: woods alloy which is Pb, Sn, Cd, and Bi, it melts at 71 o C

Metal Alloy Turkey Timer The spring is held down with a blob of solid metal. The metal alloy, which has a low melting point. When the turkey is hot enough (done!), the metal melts, releasing the spring, and the timer pops up. Turkey is done at 170 o F or 77 o C

c. Liquid solution: A solid, liquid, or gas dissolved in a liquid.  Solvent is the liquid that does the dissolving.  Solute is the substance being dissolved.  Dilute solution (unsaturated) has very little solute in a large amount of solvent. Example: Kool-aid made with only ¼ cup of sugar.  Concentrated solution has a large amount of solute dissolved in the solvent. Example: Kool-aid made with the full cup of sugar.  Saturated solution has the most solute possible dissolved in the solvent. Example: Kool-aid made with enough sugar that some stays undissolved in the bottom of the container.

Properties of Solutions Lab  What happens to the boiling point when a salt is added to H 2 O?  What happens to the freezing point when a salt is added to H 2 O?  What happens to the temperature when a salt dissolves in H 2 O?  Do all salts dissolving in H 2 O result in the same temperature change direction?  What is a precipitate?

Water Softeners Water softeners work on an ion exchange method. Ions such as Ca + 2, Mg + 2, and Fe + 3 make water hard. Hard water resists suds (or forming bubbles). Hard water also leaves deposits of these ions in pipes and fixtures.

Water softeners are filled with resin, small beads which have a large amount of surface area. When your water softener flushes, the tank with a salt brine allows the salt solutions to flow over the resin. Na +1 cling to the resin. The next few days, every time you use water, the water runs over the resin with Na +1. The Na +1 exchanges places with undesirable ions. When most of the Na +1 is gone, the water softener flushes again.

Molarity (M) is a unit of concentration. Molarity is the number of moles of solute dissolved per liter of solution. M = # of moles Volume in Liters 3 moles of NaCl are dissolved in 2 liters of solution. What is the molarity?

Remember the formula for moles 3.89 grams of NiCl 2 are dissolved in 300mL of water. What is the molarity? M = # of moles Volume in Liters Moles = Grams Molar mass

What mass of AgNO 3 would be required to make 2.5 L of 0.10 M solution?

Freezing Point Depression  T = (1.86 o C)( )(i)  T = change in temperature Kg of water: 1 Kg = 1000 mL i = number of ions formed by one molecule of ionic solid (example Na 3 PO 4  3 Na PO i = 4 ions) What will the freezing point be lowered by if 125 grams of MgCl 2 is added to 500 mL of water? Moles of ionic solid Kg of water

Acid – Base Reactions Arrhenius definition: Acid donates a H + 1 Base donates a OH - 1 HCl (aq)  H + 1 (aq) + Cl - 1 (aq) NaOH (aq)  Na + 1 (aq) + OH - 1 (aq) When mixed together, products are H 2 O and salt.

HCl (aq) + NaOH (aq)  H 2 O (L) + NaCl (aq) H + 1 (aq) + Cl - 1 (aq) +Na + 1 (aq) +OH + 1 (aq)  H 2 O (L) +Na + 1 (aq) +Cl - (aq) H + 1 (aq) + OH - 1 (aq)  H 2 O (L) HNO 3 (aq) + KOH (aq) 

Acid Rain can occur naturally. CO 2 (g) + H 2 O (L)  H 2 CO 3 (aq) Pollutants from human activities can also result in acid rain. 2 SO 2 (g) + O 2 (g)  2 SO 3 (g) SO 3 (g) + H 2 O (g)  H 2 SO 4 (aq) NO 2 (g) + H 2 O (g)  H 2 NO 3 (aq) When acid rain percolates through the ground it will react with CaCO 3 (s) (limestone), dissolving the limestone creating caves. Running and dripping water with dissolved minerals form: stalactics: deposited minerals holding tight to ceiling of cave stalagmites: deposited minerals on floor of cave

Oxidation – Reduction Reactions  All involve the transfer of e -  Metal + Nonmetal Na (s) + Cl 2 (g)  NaCl (s)  Single Replacement (metal + compound) Al (s) + Fe 2 O 3 (s)  Al 2 O 3 (s) + Fe (s) Balance equations

 Combustion reaction: Hydrocarbon combining with oxygen to produce water and carbon dioxide. C 2 H 5 OH (g) +   Synthesis: Multiple atoms or molecules combining to make one product. H 2 (g) + O 2 (g)  H 2 O (g)  Decomposition: One reactant breaking apart to make multiple products. H 2 O (L)  H 2 (g) + O 2 (g)

Review 1. Ni(NO 3 ) 2  Ni NO 3 -1 Na 2 CO 3  2 Na +1 + CO 3 -2 Ni +2 + CO 3 -2  NiCO 3 2. Ni(NO 3 ) 2 + Na 2 CO 3  NiCO NaNO 3 Ni NO Na +1 + CO 3 -2  NiCO 3 + 2Na NO 3 -1 Ni +2 + CO 3 -2  NiCO 3 3. T = 9.59 o C (or freeze at o C) M HCl M CuSO g Sr(NO 3 ) L of H 2 O

Solutions Crossword Down 1. Miscible 15. Hydration Across 10. Molality 23 Nonelectrolyte 24. (Change to 20 e - ) 33. Solvation 36. Electrolyte 45. Henry

Precipitate Lab Set ISet IISet IIISet IV Ba(NO 3 ) 2 Na 2 SO 4 FeCl 3 NiCl 2 BaCl 2 Al 2 (SO 4 ) 3 Co(NO 3 ) 2 MgCl 2 Na 2 CrO 4 Sr(NO 3 ) 2 CoCl 2 Na 2 SO 4 K 2 CrO 4 BaCl 2 NaOH NaNO 3 Ba(NO 3 ) 2 KOHBa(OH) 2 KClAlCl 3 NaNO 3 MgSO 4

Practice writing chemical equations. Pick 5 reactions from the precipitate lab, one from each set. For each reaction chosen, write: 1. Molecular chemical equation 2. Complete ionic chemical equation 3. Net ionic chemical equation