A CHEMICAL REACTION
Chemists represent a chemical reaction by writing a chemical equation. The reaction of copper with nitric acid is written as:
Cu(s) + 4HNO3(aq) à Cu(NO3)2(aq) + 2NO2(g) + 2H2O(l)
The substances to the left of the arrow are called the reactants. Those to the right of the arrow are called products. A + sign with the reactants is read “reacts with.” A + sign with the products is read as “and.” The arrow is read as “to produce.” The letters in ( ) represent the phase or state of a substance: (s) = solid, (g) = gas, (l) = liquid, (aq) = aqueous i.e. dissolved in water. Numbers before a chemical formula are called coefficients and represent the molar ratio of that substance.
The ratio of the coefficients, 1:4 à 1:2:2 in the above example indicate the lowest whole numbers of moles needed to give a complete reaction. A complete reaction is one in which no substances are over or under supplied or produced. Any combination of coefficients which adheres to the ratio will produce a complete reaction. The coefficients in the example could all be doubled (2:8 à 2:4:4) or halved (½ : 2 à ½ :1:1).
When chemicals are combined a chemical reaction may or may not occur e.g. sugar and vegetable oil do not react. A chemical reaction is indicated by observations such as: a color change, formation of a solid (a precipitate), production of a gas(bubbles), gain or loss of heat(container becomes hotter or colder), flames, rapid expansion (an explosion).
In this experiment the reaction that occurs when Alka-Seltzer is added to water will be examined. The unbalanced chemical equation is:
NaHCO3(aq) + H3C6H5O7(aq) à Na3C6H5O7(aq) + CO2(g) + H2O(l) Equation 1
Notes for completing Lab 7:
Lab 7 has data for the weights of the starting material and the sodium citrate product. What each student needs to do is to use this data to answer the questions. For Lab 7, the lecture slides (copied below into the lab) have much of the materials you need to complete the lab (balanced chemical equation, calculations for theoretical yield, etc.).
An Alka-Seltzer tablet has two substances in it: sodium bicarbonate NaHCO3 and citric acid H3C6H5O7. When the tablet is dissolved in water a chemical reaction between these two substances generates a new substance, sodium citrate Na3C6H5O7. Given what we know from the product label that a tablet contains 1.916 g of sodium bicarbonate, it is possible to calculate the theoretical amount of sodium citrate that would be formed without even doing the experiment; this calculation is described below. The calculations on page 4 of the lab do not use any experimental data, but are the calculations leading to this theoretical yield as described below. The only experimental data are the two numbers (in green) on page 3 of the lab, which are then used in step #16 that proceeds to calculate the actual experimental yield followed by the final result, the percent yield. I would suggest completing all the Chapter 7 lecture videos and lecture homework before completing this lab.
Balanced equation and calculations:
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