PERCENT POTASSIUM CHLORATE IN A MIXTURE - Worksheet

Transcription

1 35 PERCENT POTASSIUM CHLORATE IN A MIXTURE - Worksheet This lab will introduce the concept of reaction stoichiometry. We will use the mole ratios in a balanced chemical equation to calculate the amount of potassium chlorate in a sample by measuring the amount of molecular oxygen that is produced when it undergoes a decomposition reaction. A difference in chemical properties will lead to a change which can be measured in the lab, which will allow the composition of the original sample to be determined. Stoichiometry is the study of the numerical relationships in chemical formulas and reactions. Knowing the stoichiometry of a formula allows us to relate moles and grams for particular reactants or products (i.e., that 1 mole of H O weighs 18.0 g). Knowing the stoichiometry of a reaction allows us to relate amounts of different substances to each other, and allows us to predict how much of the product(s) will be formed, or how much of the reactant(s) will be needed. Since moles combine in the same ratio that atoms, molecules, or formula units do, the coefficients in a balanced chemical reaction specify the relative amounts in moles of each of the substances involved in the reaction. For example, consider the reaction between hydrogen and oxygen to make water: H (g) + O (g) H O(g) The coefficients of this reaction can be interpreted in two different ways: This many molecules of H react with molecules of O to make molecules of H O H (g) + 1 O (g) H O(g) This many moles of H react with moles of O to make moles of H O This means that the coefficients can be used as conversion factors to relate the number of moles of one chemical to the number of moles of another chemical: or, if we rewrite these relationships as ratios: moles of H = 1 mole of O moles of H = moles of H O 1 mole of O = moles of H O mol H 1mol O mol H mol H O 1mol O mol H O

2 36 (The reciprocals of these relations are of course also valid ratios.) These relationships are true only for this particular balanced equation. A different chemical equation will have its own unique set of relationships, derived from the coefficients in that reaction. For example, suppose we have 3.0 grams of O in the above reaction. We can use the balanced equation to determine how many grams of H will be needed, and how many grams of H O will be produced: Convert g O to mol O : 1mol O 3.0 g O = 1.00 mol O 3.00 g O Convert mol O to mol H : coefficient that we want mol H 1.00 mol O =.00 mol H 1mol O coefficient that we started with initially Convert mol H to g H :.0 g H.00 mol H = or, we can put everything together in a single calculation, How many grams of water will be formed? 4.04 g H 1mol H 1mol O mol H.0 g H 3.0 g O = 4.04 g H 3.00 g O 1mol O 1mol H 1mol O mol HO 18.0 g HO 3.0 g O = 36.0 g HO 3.00 g O 1mol O 1mol H O In this experiment, the number of moles of O can be used to calculate the number of moles of KClO 3 in the original sample, and therefore the number of grams of KClO 3 in the sample. From the mass of KClO 3 and the mass of the sample, the percentage of KClO 3 in the sample can then be determined.

3 Name: 37 Percent Potassium Chlorate in a Mixture - Worksheet Write and/or balance the following equations. Remember the seven diatomic elements! Use the mole ratios from the balanced equations to solve the following problems. Show your work in all steps for full credit and make sure you use significant figures on all problems. 1. Potassium chlorate decomposes into potassium chloride and oxygen gas Part I. How many moles of oxygen are produced when 3.0 moles of potassium chlorate decompose completely? 3. How many moles of potassium chlorate are needed to produce 11.7 moles of oxygen gas? 4. Butane (C 4 H 10 ) undergoes combustion. C 4 H 10 (l) + O (g) CO (g) + H O(l) 5. How many moles of butane are needed to create 3.7 moles of water? 6. How many grams of CO are produced when 88 g of O are reacted with an excess of butane?

4 38 7. Water decomposes into hydrogen gas and oxygen gas by electrolysis. 8. How many grams of hydrogen will be produced when 6.0 moles of oxygen are produced? 9. How many grams of water are required to produce 9.00 grams of hydrogen? 10. Ammonium dichromate decomposes into gaseous water, gaseous nitrogen and solid chromium(iii) oxide. 11. How many grams of ammonium dichromate are required to produce 34.0 g of chromium(iii) oxide? 1. How many total grams of gas are created when 454 g (1 pound) of ammonium dichromate is allowed to decompose?

5 13. Cobalt(II) chloride reacts with fluorine in a single replacement reaction to produce cobalt(ii) fluoride and chlorine gas. 39 CoCl + F à CoF + Cl 14. How many grams of fluorine are required to produce 90.8 g of cobalt(ii) fluoride? 15. Solid iron(iii) oxide reacts with hydrogen gas to form iron and water. 16. How many grams of iron are produced when 450. grams of iron(iii) oxide are reacted? 17. An impure sample of iron(iii) oxide measuring 11.1 g reacts with an excess of hydrogen gas, and 54.0 g of pure iron is isolated. Assuming the hydrogen gas doesn t react with the impurities, how much iron(iii) oxide was present in the original sample? What is the percent iron(iii) oxide in the original sample?

6 Potassium chlorate decomposes into potassium chloride and oxygen gas Part II 19. A.0 g of impure potassium chlorate is heated, and g of solid material remains. How many grams of oxygen were lost upon heating this reaction? 0. How many moles of oxygen were lost upon heating? 1. How many moles of potassium chlorate were present in the original mixture?. How many grams of potassium chlorate were present in the original mixture? 3. What percentage of the original mixture consisted of potassium chlorate?