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Solution Stoichiometry Guides

  • Stoichiometry
  • Balancing Redox Half-Reactions
  • Acid-Base
  • Titrations

Steps for Solving Stoichiometry Problems

  1. Find out what ions are present in the solution after the reaction has occurred. Basically split the compounds that can dissociate and leave the solids as they are.

  2. Write the final balanced net ionic equation for the overall reaction.

  3. Calculate the number of moles of reactants using the information (usually the mass of the reactant) given.

  4. Using that, find out which reactant is the limiting reagent.

  5. Using the limiting reagent, calculate the number of moles of products formed.

  6. Convert the moles of products back to grams.

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Steps for Balancing Redox Half-Reactions in Acidic Solutions

  1. Separate the original equation into oxidation and reduction half reactions.

  2. For each of the half reaction balance all the major elements first. Then balance the oxygen using H2O, hydrogen using H­+, and charge using electrons.

  3. If the number of electrons for the half-reactions do not match, multiply one or both by the lowest common denominator.

  4. Add the half-reactions together and cancel out the common species. They can only be canceled out if one is on the reactant side of on half-reaction and the other is on the product side of the other half-reaction.

  5. Check and make sure that the elements and charges are balanced and equal.

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How to perform Acid-Base Reactions

  1. First write the equation and balance it.
  2. Calculate the moles in the reactants using the information given (usually the volume and the molarity).
  3. Find the limiting reactant.
  4. Then, with the limiting reactant, use mole ratios to find the amount of products that can be formed.

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Titrations

A titration is when you add a strong acid and a strong base at a precise amount so that the pH of the solution will become 7, or the equivalence point. You can determine the equivalence point by using an indicator, which changes the color of the solution when the solution reaches a certain pH. Phenolphthalein is a base indicator that indicates when a solution is over the pH of 9, it will turn pink. The endpoint of the solution is when the whole solution turns to the color. In order for a titration to be successful, the following must happen:

  1. The reaction between the known and unknown solutions must be determined.
  2. The equivalence point must be accurately determined.
  3. The volume of the known solution needed to reach the equivalence point must be known.

When the process is done correctly, it is known as an acid-base reaction.

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