Quantitative Relationships (Stoichiometry)

1. Science 20 Quantitative Relationships (Stoichiometry)

2. Review of Classifying and Balancing Chemical Equations • Lets take a moment… sit back… relax… and review some previously learned concepts…

3. 6 main types of chemical reactions: • Formation (simple composition): elements  compound • Simple decomposition: compound  elements • Single replacement: element + compound  element + compound • Double Replacement: compound + compound  compound + compound • Complete combustion: substance + oxygen  most common oxides • Other: any reaction that does not fit in the above categories

4. The coefficients that are placed in front of the compounds and elements represent the mole-to-mole ratio of the reactants and products. Ex. 2NaCl(aq) + MgSO4(aq)→ Na2SO4(aq) + MgCl2(s) • 2 moles of sodium chloride reacts with one mole of magnesium sulfate to produce one mole of sodium sulfate and one mole of magnesium chloride • When you are making quantitative calculations, please use the mole-to-mole ratio in your calculations :

5. Mole-to-Mole Stoichiometry • Calculations that make use of a balanced equation and information about one substance to calculate information about a different substance are called stoichiometric calculations • The simplest stoichiometric calculations are those where the quantities are measured in moles.

6. Follow these steps for mole-to-mole questions: • Write balanced equation for the reaction. Determine the two substances involved as being the given or the unknown. • Determine the number of moles of one substance. • Set up a mole ratio using coefficients of the balanced equation for the two substances. Substitute values in mole ratio for the given and unknown. • Solve the equation.

7. Example • How many moles of oxygen gas are needed to react completely with 3.50 mol of hydrogen gas to produce water vapor? 1)Write balanced equation for the reaction. 2H2(g) + O2(g)→ 2H2O(g) 2) Determine the two substances involved as being theknownor the unknown. Known: 3.50 mol of hydrogen Unknown: ? mol of oxygen

8. 3) Multiply the known amount of moles by the unknown molar coefficient and divide by the known molar coefficient. n xn unknown n known 3.50 mol H2 x 1 mol O2 2 mol H2 4) Solve the equation. nO2 = 1.75 mol 2H2(g) + O2(g)→ 2H20(g)

9. Try this one… Example 1: Nitrogen monoxide gas may be prepared by reacting copper metal with dilute nitric acid. 3Cu(s) + 8HNO3(aq)→ 3Cu(NO3)2(aq) + 2NO(g) + 4H20(l) Determine the number of moles of nitrogen monoxide that can be obtained from the reaction of 0.75 moles of copper with an excess of nitric acid.

10. Mole-to-Mass Stoichiometry • When we carry out a chemical reaction, we usually measure solids by their masses. • To perform mole to mass stoichiometric calculations, follow these steps: • Write a balanced equation for the reaction. • Determine the number of moles of one substance. • From the balanced equation, set up a mole ratio using coefficients of the balanced equation for the two substances. Substitute values in mole ratio for the given and the unknown. Solve the equation for the unknown number of moles. • Convert unknown moles into mass. (m=nxM)

11. Example 2: Copper metal reacts with a solution of silver nitrate to produce silver and copper (II) nitrate. What mass of silver can be produced by reacting 0.250 mol of copper?

12. Example 3: Sulfuric acid is neutralized by sodium hydroxide solution. What mass of sodium sulfate can be produced by reacting 0.350 mol of NaOH(aq)?

13. Mass-to-Mole Stoichiometry • In a mass-to-mole problem, you will be given the mass of a substance and you will determine the number of another substance. • For these types of questions, please follow these steps: • Write a balanced equation for the reaction. • Calculate the number of moles for the given substance. (n = m/M) • Set up a mole ratio using coefficients of the balanced equation for the two substances.Substitute values in the mole ratio for the known and the unknown. • Solve the equation for the unknown number of moles.

14. Example 4: How many moles of water vapor can be produced by reacting 101g of oxygen gas with sufficient hydrogen gas?

15. V. Mass-to-Mass Stoichiometry • In this type of question, you are provided with the mass of one substance and asked to calculate the mass of another substance in the equation. • To solve these types of problems, follow these steps. • Write a balanced equation for the reaction. • Calculate the number of moles for the given substance. (n = m / M) • Set up a mole ratio for the known and unknown. Solve the equation for the unknown number of moles. • Convert unknown number of moles to mass. (m = n x M)

16. Example 5: What mass of aluminum oxide must be decomposed to produce 80.0 g of oxygen gas?

17. Hint of Gravimetric (Mass) Stoichiometry **When dealing with mass stoichiometry, be sure to convert all masses to moles before performing the mole ratio.

18. Volume to Volume Stoichiometry • In this type of question, you are working with solutions. • To perform solution problems, follow these steps: • Write a balanced chemical equation. Determine the two substances involved as being the given quantity and the unknown quantity. • Calculate the number of moles of the given substance using n = c x v • From the balanced equation, set up a mole ratio using coefficients of the balanced equation for the two substances. Substitute values in mole ratio for the given and the unknown. Solve the equation for the unknown number of moles. • Convert the number of moles to a volume.

19. Example 6: What volume of a 0.250 mol/L hydrochloric acid is needed to completely react with 250 mL of a 0.156 mol/L magnesium hydroxide solution?

20. Combined Questions • You will encounter questions where you will have to convert from mass to volume or volume to mass, etc. • Use the steps previously provided for you, but adjust the steps to the specific situation in the question.

21. Review of Stoichiometry • Calculations that make use of a balanced chemical equation are known as stoichiometric calculations. • The common feature to all stoichiometric calculations is the use of the mole relationships indicated in a balanced equation.

22. Summary of steps for any stoichiometry question: • Always write a correctly balanced chemical equation. • Change the given / known quantity to mole using one of the following equations. { n = m/M or n = C∙V} • Find the required or unknown number of moles using the mole to mole ratio. • Convert the required number of moles to volume, mass, or concentration using the appropriate formula. {v = n/c or m = nM or c = n/v}

23. Question 1: Aluminum metal can be refined from the ore of aluminum called bauxite. In the refining process aluminum oxide decomposes to aluminum and oxygen gas. What mass of aluminum can be produced from 2.04 kg of aluminum oxide? 2 Al2O3(s)→ 4 Al(s) + 3 O2(g)

24. Question 2: • Iron (III) phosphate reacts with tin (IV) nitride to produce iron (III) nitride and tin (IV) phosphate. 4 FePO4(aq0 + Sn3N4(aq)→ 4 FeN(aq) + Sn3(PO4)4(aq) • How many moles of tin (IV) nitride are needed to produce 0.0500 mol of iron (III) nitride? • How many moles of iron (III) phosphate are used when 0.045 mol of tin (IV) nitride also reacts?

25. Question 3: Ammonia reacts with hydrochloric acid to produce ammonia chloride. What mass of ammonia is needed to produce 36.1g of ammonium chloride? NH3(g) + HCl(aq)→ NH4Cl(s)

26. Question 4: 150 mL of a 0.367 mol/L solution of sodium nitrate reacts with 225 mL of potassium carbonate. What is the concentration of the potassium carbonate solution? 2 NaNO3(aq) + K2CO3aq) → Na2CO3(asq) + 2 KNO3aq

27. Question 5: Sodium chloride solution reacts with 100 mL of a 1.50 mol/L solution of silver nitrate. Using the following equation, calculate the mass of precipitate produced. Na2S(aq) + 2 AgNO3(aq)→ 2 NaNO3(aq) + Ag2Ss)