When baking soda is heated, carbon dioxide is produced. In this experiment you will investigate the reaction taking place when the sodium hydrogencarbonate in baking soda is thermally decomposed. FA 4 is baking soda (impure NaHCO3). Its composition is the same as that of FA 2.

1. (a)Method Record all your readings in the space below. • Weigh the crucible with its lid. • Transfer all the FA 4 from the container into the crucible. • Weigh the crucible, lid and FA 4. • Calculate and record the mass of FA 4 used. • Place the crucible and contents on a pipe-clay triangle. • Heat gently, with the lid on, for approximately one minute. • Heat strongly, with the lid off, for a further three minutes. • Replace the lid and leave the crucible to cool for at least five minutes. While the crucible is cooling you may wish to begin work on Question 3. • When it is cool, weigh the crucible with its lid and contents. • Heat strongly, with the lid off, for a further two minutes. • Replace the lid and leave the crucible to cool for at least five minutes. • When it is cool, weigh the crucible with its lid and contents. • Calculate and record the mass of residue obtained. • This residue is FA 5. Keep this for use in 2(d). Results[4]
2. (b)(i)Use the percentage purity by mass of FA 2 you calculated in 1(c)(v), to calculate the mass of sodium hydrogencarbonate in the sample of FA 4 that you weighed out. (If you were unable to carry out the calculation in 1(c)(v), assume that the percentage purity by mass of FA 2 is 95.8%.) mass of NaHCO3 in FA 4 weighed out = ................................. g[1]
3. (b)(ii)Calculate the mass of impurity present in your sample of FA 4. mass of impurity = ................................. g[1]
4. (b)(iii)The impurity in FA 4 does not decompose when it is heated. This means that the residue, FA 5, contains the mass of impurity calculated in (ii) together with the solid decomposition product of sodium hydrogencarbonate. Calculate the mass of the solid decomposition product. mass of solid decomposition product = ................................. g[1]
5. (b)(iv)Use your answers to (i) and (iii) to calculate the mass of solid decomposition product that would be obtained if 84.0 g of pure sodium hydrogencarbonate were heated. mass of solid decomposition product = ................................. g[1]
6. (b)(v)A student carried out the experiment by heating to constant mass and calculated that heating 84.0g of pure NaHCO3 would produce 52.3 g of the solid decomposition product. The student then suggested the following equation for the thermal decomposition of sodium hydrogencarbonate. NaHCO3(s) → NaOH(s) + CO2(g) Use data from the Periodic Table on page 12 to explain why the student's suggestion cannot be correct.[4]
7. (c)(i)Why was the lid put on while the crucible and its contents cooled?[1]
8. (c)(ii)The experiment could be made more accurate by heating to constant mass or using a more accurate balance. Suggest a further improvement to make the experiment more accurate.[1]
9. (d)(i)Pour a 1 cm depth of sulfuric acid, FA 1, into a test-tube. Add some FA 5 from the crucible to the acid in the test-tube. Record all your observations.[2]
10. (d)(ii)Use your observation(s) in (i) to identify an anion present in FA 5. Explain your answer. identity explanation[1]
11. (d)(iii)Steam is one of three products obtained when sodium hydrogencarbonate is thermally decomposed. Use your answer in (ii) to complete and balance the equation for the thermal decomposition of sodium hydrogencarbonate. Include state symbols. ........NaHCO3(s) → .H2O(g) + ........CO2(g) +[1]
12. (d)(iv)State whether the balanced equation in (iii) agrees with the student's results given in 2(b)(v). Show working in order to explain your answer.[4]