Presentation is loading. Please wait.

Presentation is loading. Please wait.

Mass Relationships in Chemical Reactions Chapter 3.

Similar presentations


Presentation on theme: "Mass Relationships in Chemical Reactions Chapter 3."— Presentation transcript:

1 Mass Relationships in Chemical Reactions Chapter 3

2 Natural lithium is: 7.42% 6 Li (6.015 amu) 92.58% 7 Li (7.016 amu) 100 = _______ amu 3.1 Average atomic mass of lithium:

3 The mole (mol) is the amount of a substance that contains as many elementary entities as there are atoms in exactly ______ grams of 12 C mol = N A =____________________ ___________________ number (N A )

4 Molar mass is the mass of 1 mole of in grams eggs shoes marbles atoms 1 mole 12 C atoms = ____________ atoms = ______ g 1 12 C atom = amu 1 mole 12 C atoms = ___________ g 12 C 1 mole lithium atoms = ___________ g of Li For any element ___________ (amu) = __________ (grams) 3.2

5 One Mole of: C S Cu Fe Hg 3.2

6 _____ g = ________________ amu 3.2 M = molar mass in g/mol N A = Avogadros number 1 amu = ______________ g

7 Do You Understand Molar Mass? How many atoms are in g of potassium (K) ? 3.2

8 Molecular mass (or molecular weight) is the sum of the atomic masses (in amu) in a molecule. SO 2 1Samu 2Oamu SO 2 amu For any molecule ________ mass (amu) = ______ (grams) 1 molecule SO 2 = _________ amu 1 mole SO 2 = ________ g SO 2 3.3

9 Do You Understand Molecular Mass? How many H atoms are in 72.5 g of C 3 H 8 O ? 3.3

10 Percent composition of an element in a compound = n x molar mass of element molar mass of compound x 100% n is the number of moles of the element in 1 mole of the compound C2H6OC2H6O 3.5

11 Types of Formulas ____________ Formula____________ Formula The formula of a compound that expresses the _________________ ratio of the atoms present. Ionic formula are always ____________ formula _______ Formula_______ Formula The formula that states the _____ number of each kind of atom found in _________ of the compound.

12 To obtain an Empirical Formula 1.Determine the _______________ of each element present, if necessary. 2.Calculate the number of _________ of each element. 3.Divide each by the smallest number of moles to obtain the_______________. 4.If _____numbers are not obtained * in step 3), multiply through by the _____ number that will give all whole numbers * Be careful! Do not round off numbers prematurely

13 A sample of a brown gas, a major air pollutant, is found to contain 2.34 g N and 5.34g O. Determine a formula for this substance. require mole ratios so convert grams to moles

14 Calculation of the Molecular Formula A compound has an empirical formula of NO 2. The colourless liquid, used in rocket engines has a molar mass of 92.0 g/mole. What is the molecular formula of this substance?

15 Empirical Formula from % Composition A substance has the following composition by mass: % Na ; % B ; % H What is the empirical formula of the substance? Consider a sample size of _____ grams This will contain: _____ grams of Na, ______ grams of B, and _____ grams H Determine the number of ______ of each Determine the ________ number ratio

16 3.6 g CO 2 mol CO 2 mol Cg C g H 2 O mol H 2 Omol Hg H g of O = g of sample – (g of C + g of H) Combust 11.5 g ethanol Collect 22.0 g CO 2 and 13.5 g H 2 O 6.0 g C = 0.5 mol C 1.5 g H = 1.5 mol H 4.0 g O = 0.25 mol O Empirical formula C 0.5 H 1.5 O 0.25 Divide by smallest subscript (0.25) Empirical formula C 2 H 6 O

17 1.Write balanced chemical equation 2.Convert quantities of known substances into moles 3.Use coefficients in balanced equation to calculate the number of moles of the sought quantity 4.Convert moles of sought quantity into desired units Mass Changes in Chemical Reactions 3.8

18 Other units Molarity –Moles solute / L solution Gases –22.4 L = 1 mole of ANY GAS at STP

19 Methanol burns in air according to the equation 2CH 3 OH + 3O 2 2CO 2 + 4H 2 O If 209 g of methanol are used up in the combustion, what mass of water is produced? 3.8

20 6 green used up 6 red left over Limiting Reagents 3.9

21 Method 1 Pick A Product ????? The ____ answer will be the correct answer The _____that gives the _____answer will be the _______ reactant

22 Limiting Reactant: Method g of aluminum reacts with 35.0 grams of chlorine gas to produce aluminum chloride. Which reactant is limiting, which is in excess, and how much product is produced? 2 Al + 3 Cl 2 2 AlCl 3 Start with Al: Now Cl 2 :

23 Method 2 Convert one of the reactants to the _____ See if there is enough _______ to use up the other ______ If there is less than the ______amount, it is the ______ reactant Then, you can find the desired species

24 Do You Understand Limiting Reagents? In one process, 124 g of Al are reacted with 601 g of Fe 2 O 3 2Al + Fe 2 O 3 Al 2 O 3 + 2Fe Calculate the mass of Al 2 O 3 formed. 3.9

25 Use limiting reagent (Al) to calculate amount of product that can be formed. g Almol Almol Al 2 O 3 g Al 2 O 3 3.9

26 Finding Excess Practice 10.0g of aluminum reacts with 35.0 grams of chlorine gas 2 Al + 3 Cl 2 2 AlCl 3 We found that _______ is the limiting reactant, and _______ of aluminum chloride are produced. Given amount of excess reactant Amount of excess reactant actually used Note that we started with the limiting reactant! Once you determine the LR, you should only start with it!

27 ___________ is the amount of product that would result if all the limiting reagent reacted. _________ is the amount of product actually obtained from a reaction. % Yield = _________Yield x


Download ppt "Mass Relationships in Chemical Reactions Chapter 3."

Similar presentations


Ads by Google