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Stoichiometry. Stoichiometry is the part of chemistry that studies amounts of substances that are involved in reactions. It could be amounts of substances.

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Presentation on theme: "Stoichiometry. Stoichiometry is the part of chemistry that studies amounts of substances that are involved in reactions. It could be amounts of substances."— Presentation transcript:

1 Stoichiometry

2 Stoichiometry is the part of chemistry that studies amounts of substances that are involved in reactions. It could be amounts of substances before the reaction or amount of material that is produced by the reaction. Stoichiometry is all about amounts.

3 What a balanced chemical equation tells us A chemical equation represents the mole ratio of reactants and products CuCl 2 + 2AgNO 3 2AgCl + Cu(NO 3 ) 2 1mol 2mol 2mol 1mol NaOH + HCl NaCl + H 2 O 1mol 1mol 1mol 1mol 2CO + O 2 -> 2CO 2 2mol 1mol 2mol Mg + 2HCl -> MgCl 2 + H 2 1 mol 2 mol 1 mol 1 mol

4 Stoichiometry will tell you that if you have ten million atoms of sodium (Na) and only one atom of chlorine (Cl) you can only make one molecule of sodium chloride (NaCl). Nothing you can do will change that. Like this: 10,000,000 Na + 1 Cl --> NaCl + 9,999,999 Na

5 Limiting reagent A reagent is another word for reactant A reaction will stop when one reactant is used up before the other This is called a limiting reagent The other reactant is the excess reagent Blue is the limiting reagent Red is the excess reagent

6 Limiting reagent 2H 2 + O 2 2H 2 O Initial mol Reaction mol Final mol 0 2 8

7 Mass-Mass stoichemtry Involves solving a problem in which the mass of a reactant or a product is given

8 Calculating the mass of a substance given the mass of another reactant or product 1.Write a balanced chemical equation 2.Identify known and unknown quantities of substances 3.Calculate the number of moles of known quantities 4.Find the molar ratio and use this to calculate the number of moles of a required substance Mol of required substance = Molar ratio Mol of given substance 5. Calculate the quantity o the required, unknown, substance

9 Calculations Calculate the number of moles of CO 2 formed in the combustion of ethane C 2 H 6 in a process when 35.0 mol of O 2 is consumed. The reaction is: 2 C 2 H O 2 4 CO H 2 O 4 CO 2 : 7 O mol O 2 x 4 CO 2 mol = 20.0 mol CO 2 7 mol O 2 mol

10 Two moles of Mg and five moles of O 2 are placed in a reaction vessel, and then the Mg is ignited according to the reaction Mg + O 2 MgO. Identify the limiting reagent in this experiment. 2 Mg + O 2 2 MgO 2 mol 1mol (I have 5, 5 -1 = 4 mol unused) Four moles of oxygen will remain unreacted. Oxygen is the excess reagent, and Mg is the limiting reagent.

11 What mass of iron (III) oxide is formed from the complete combustion of 183.5g of pyites (FeS 2 ) FeS 2 + O 2 Fe 2 O 3 + SO 2 1.4FeS O 2 2Fe 2 O 3 + 8SO 2 2.molar mass of FeS 2 = (2 x 32.1) = g/mol = 183.5g x 1 mol g = mol

12 3. Find the molar ratio of 4FeS 2 to 2Fe 2 O 3 4:2 2:1 Mol of Fe 2 O 3 = 2 FeS 2 = = mol 2 Mol of Fe 2 O 3 = mol 4. Molar mass of Fe 2 O 3 = 2 x x 16 = 159.7g/mol mol x 159.7g 1mol = 122.1g of Fe 2 O 3

13 Calculate the mass of water produced when 2.8g of CH4 is burnt in the air 1.CH 4 + 2O 2 2H 2 O + CO 2 2.Molar mass = = 16g/mol Mol of CH 4 = 2.8g x 1 mol 16g Mol of CH 4 = mol 3. Molar ratio CH 4 : H 2 O 1:2 CH 4 = 1 = mol = mol of H 2 O H 2 O Molar mass of H20 = 2+16 = 18g/mol Mass of H20 = mol x 18g = 1.575g 1 mol

14 Limiting reagent How much precipitate can you make with only 2.6mol of KCl? AgNO3 + KCl AgNO 3(aq) + KCl (aq) AgCl (s) + KNO 3(aq) 2.6mol KCL is the limiting reagent we only have a certain amount of it

15 1.Balance equation AgNO 3(aq) + KCl (aq) AgCl (s) + KNO 3(aq) 1.Determine molar ratio 2.KCl to AgCl is 1:1 I have 2.6mol of KCl I have 2.6 mol of AgCl Molar mass of AgCl = g/mol 2.6mol KCl x 1mol of AgCl x g of AgCl 1 mol of KCL 1mol of AgCl = g of AgCl

16 If 6.3g of S 8 react with Pb, how many grams of PbS are formed? Pb + S 8 PbS 8Pb + S 8 8PbS 6.3g ? Molar mass of S8 = x 8 = g/mol Mol of S8 = 6.6g x 1mol g = mol Molar ratio = PbS 8 S8 1 Mol of PbS = 8 x = mol Molar mass of PbS = g/mol Mass of PbS = 1.647mol x g 1 mol = g

17 Determine the limiting reagent What mass of liquid water is formed when 2.3g of H 2 gas and 4.55g of O 2 gas react together 1.2H 2 + O 2 2H 2 O 2.2.3g 4.55g Molar mass of H2 = 2g/mol Mol of H2 = 2.3g x 1mol = 1.15mol 2g Molar mass of 02 = 32g/mol Mol of O2 = 4.55 x 1 mol = 0.142mol 32g

18 2H 2 + O 2 2H 2 O x 2 = 0.284mol of H2 Which is the limiting reagent? H 2 + O 2 2H 2 O Molar mass of H 2 O = 18g/mol Mass of H 2 O = 0.282mol x 18g 1 mol = 5.076g

19 What volume of 0.100mol/L H 2 SO4 acid reacts completely with 17.8mL of 0.15 of potassium hydroxide? Acid + base salt + water KOH + H2SO4 K2SO4 + H20 2KOH + H2SO4 K2SO4 + 2H M 0.1M 17.8mL ? (0.0178L) Mol of KOH = L x 0.15mol 1L = mol Molar ratio = H2SO4 1 KOH 2 Mol of H2SO4 = ½ x mol L of H2SO4 = mol x 1L 0.1mol L of H2SO4 = L

20 Zinc metal is reacted with 400mL of a 0.25mol/L solution of sulfuric acid. Calculate the mass of zinc sulfate formed

21 Questions Pg 263 Q 1, 2, 4, 6,7,8 Pg 267 Q 9

22 Titration A titration is a method of analysis that will allow you to determine the precise endpoint of a reaction and therefore the precise quantity of reactant in the titration flask. A buret is used to deliver the second reactant to the flask and an indicator or pH Meter is used to detect the endpoint of the reaction.

23 ence/chemistry/experiments/ethanoic_acid _vinegar/index.htm


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