Stiochiometry F09

Stiochiometry F09 - Experiment 3 Stoichiometry Laws to...

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Experiment 3: Stoichiometry: Laws to Moles to Molarity Objective To determine the mass of a product of a chemical reaction To make a solution of assigned molarity Grading Lab Report (90%) TA points (10%) Before Coming to Lab. .. Read the lab instructions Complete the online quiz Introduction The word stoichiometry derives from two Greek words: stoicheion (meaning "element") and metron (meaning "measure"). Stoichiometry deals with calculations about the masses (sometimes volumes) of reactants and products involved in a chemical reaction. Consequently, it is a very mathematical part of chemistry. In the first part of this lab, sodium bicarbonate is reacted with an excess of hydrochloric acid. O H (g) CO NaCl(aq) HCl(aq) (s) NaHCO 2 2 3 + + + By measuring the mass of NaHCO 3 and balancing the equation (above), the mass of NaCl expected to be produced can be calculated and then checked experimentally. Then, the actual amount of NaCl produced can be compared to the predicted amount. This process includes molar ratios, molar masses, balancing and interpreting equations, and conversions between grams and moles and can be summarized as follows: 1. Check that the chemical equation is correctly balanced. 2. Using the molar mass of the given substance, convert the mass given in the problem to moles. 3. Construct a molar proportion (two molar ratios set equal to each other). Use it to convert to moles of the unknown. 4. Using the molar mass of the unknown substance, convert the moles just calculated to mass.
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In the second part of this lab, since a great deal of chemistry is done with solutions, a solution will be prepared of allocated molarity. Molarity, or more correctly molar concentration, is defined to be the number of moles of solute divided by the number of liters of solution: solution substance M V n c = with units of [mole/L]. However molar concentration depends on the temperature so a higher temperature would result in an increased volume with a consequential decrease in molar concentration. This can be a significant source of error, of the same order as the error in the volume measurements of a burette, when the temperature increases more than 5 ºC. Steps to preparing a solution of a certain concentration:
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Stiochiometry F09 - Experiment 3 Stoichiometry Laws to...

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