Experiment 8 Conservation of Mass kussion: action: 170 Mole wt. g/mol Aqual the combined masses of all the reactants that were initially present. Furthermore, we fter any chemical reaction, the total mass of new products and any left over reactants) will a predict the mass of each product that will be formed if we know the molecular weight or the formula (from which we can predict the molecular weight). As an example, consider the dissolve the two substances in water, mix the solutions and then compare the masses (weights) of To confirm the identification of each product, we will perform a chemical test for AgNO3 + KBr → AgBr + KNO3 119 188 101 289g 289g the products with those of the reactants. The reaction is: carbonate and a flame test for the strontium. Total weight If we weigh 170 grams of AgNO3 and dissolve it in water and do the same for 119 grams of KBr, we can combine the two solutions and cause the reaction to occur. A white precipitate iams, which settles to the bottom of the beaker if left undisturbed, because one of the two products, either AgBr or KNO3, is water insoluble. The other is soluble in water and we are not stating beforehand which is which. Then, suppose we filter the solution, collecting the precipitate on the filter paper and the solution in a beaker. After the precipitate has dried and the water boiled from the solution, we may determine the weights of each solid. If the precipitate has a mass of 188 grams (or near this), it can be positively identified as the silver bromide. Conversely, if it has a mass of 101 frams, it must be potassium nitrate. The other solid will show the alternate mass. In this experiment, we will not actually use silver nitrate because of its cost. Instead, we will use strontium nitrate Sr(NOx), and potassium carbonate (K,CO2) and the quantities will be scaled down by a factor of 100. But the idea is the same as in our other example; that is, we will + 2 KNO Sr(NO3)2 + K2CO3 → SrCoz

point, you should have about 100 mL of filtrate). Gently boil the filtrate to remove the water and Determine the molecular weight of each reactant and product; then compute the weight of 0.0100 mole quantity for cach reactant. Obtain two small beakers and add about 30 ml of RO water in each. Then dissolve 0.0100 mole of Sr(NO), in one beaker and 0.0100 mole of K,Co, in the other. When the solutions are homogeneous, slowly pour the K,CO, solution into the Sr(NO), with stirring. Warm the mixture over a low flame until the solid settles out (five to Meanwhile, assemble a filtering apparatus consisting of a pre-weighed, folded filter paper in your funnel mounted on a ring stand. (Your instructor will probably comment on the filtering technique.) Filter the white mixture carefully and collect the filtrate in a pre-weighed 250 ml beaker. Rinse out the reaction beaker with small portions of distilled (RO) water, filter rinsings and collect all of these filtrates. Finally wash the white precipitate thoroughly with about 25 mL of RO water directed from a squirt bottle, and collect this filtrate with the others (at this 32 Procedure: Na Loc Deter eight minutes), then let it cool. Calcul the Mass o (1) precover the other product. As the solution approaches dryness, stop heating and let the small amount of remaining water evaporate on its own (if this residue itself is heated with the burner, it may melt thereby giving the appearance of still being wet). When cool, weigh the contents and obtain the net weight of your residue. While you are keeping one eye on the filtrate, remove the damp filter paper from the funnel, spread it onto a watch glass, and set it carefully in your locker to dry until the next lab period. At that time, weigh the dried product and obtain the net weight of the white precipitate. Tabulate your data on the report sheet. M N. М. Ma Test for carbonate: Place a few small crystals of the residue and precipitate into two different small test tubes. Add five drops of 1 M HCl to each test tube. The carbonate should show an effervesence of carbon dioxide. Net (2) Tota Diffe Test for strontium: Fill a third test tube to a depth of 2 to 3 cm with the 3M HCI. Clean a nichrome wire by dipping it in the HCl and then heating in a burner flame until most of the yellow-orange flame is gone. It may be necessary to dip and heat more than once to accomplish this. To test the solutions, dip the cleaned wire into the first test tube and then place it in the flame. Strontium imparts a bright crimson color to the flame; potassium will cause a violet flame. Repeat this for the second tube. Be sure to clean the wire between tests. Results of ch HCI Flame

Residue In what way? 6. If your recovered mass of SrCoz did not agree with your predicted mass in question two, suggest a possible reason for the difference. и th tot vo Solu mol Decr 5. Do your chemical tests confirm these results?