Review-Molecular Formula

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# Review-Molecular Formula - PowerPoint PPT Presentation

Review-Molecular Formula. Nicotine, a component of tobacco, has an empirical formula of C 5 H 7 N. The molar mass of nicotine is 162 g. What is its molecular formula? A compound contain 64.9% C, 13.5% H, and 21.6% O. Its molecular mass is 74 g. Find the molecular formula.

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Review-Molecular Formula
• Nicotine, a component of tobacco, has an empirical formula of C5H7N. The molar mass of nicotine is 162 g. What is its molecular formula?
• A compound contain 64.9% C, 13.5% H, and 21.6% O. Its molecular mass is 74 g. Find the molecular formula.

### Unit 10:Chemical Equations

Chapter Objectives
• 1. To learn to write chemical equations
• 2. To correctly interpret chemical equations
• 3. To balance chemical equations
Chapter Objectives
• 4. To classify chemical reactions
• 5. To predict products of chemical reactions
• 6. To write ionic and net ionic equations
Chemical Reactions
• In a chemical reaction, substances join together to form new substances
• The original substances present are called REACTANTS
• The new substances formed are called PRODUCTS
Discussion of Chemical Reactions
• The general form of an equation is:
• Reactants  Products
• The  is read as “yields” or “reacts to produce”
Discussion of Chemical Reactions
• A + B  C
• Substance “A” and “B” react to produce substance “C”
Additional Symbols in Chemical Reactions
• + used to separate reactants or products
• (s) means chemical is in solid state
• (l) means chemical is in liquid state
Additional Symbols in Chemical Reactions
• (g) means chemical is in gas state
• (aq) means chemical is dissolved in water
• *See Table 10-1 in book (page 278)
Other Symbols
•  means something is added to the reaction
• Usually this is heat
• Pt means a catalyst (Pt) is added
Skeleton Equations
• Skeleton (Formula) Equation- the rough form of an equation
• It only shows the framework for the chemical reaction
Write Skeleton Equations
• Sodium metal reacts with Oxygen gas to form solid Sodium Oxide
• Solid sulfur reacts with Fluorine gas to form gaseous Sulfur Hexafluoride when heated
• Nitrogen reacts with Hydrogen to form Ammonia (NH3) gas. Heat is required.
Review-Write Skeleton Equations
• 1. Magnesium metal reacts with Chlorine to form solid Magnesium Chloride.
• 2. Aqueous Silver Nitrate reacts with aqueous Sodium Chloride to form solid Silver Chloride and aqueous sodium nitrate
Law of Conservation of Mass
• The Law of Conservation of Mass states that mass is neither created or destroyed in a chemical reaction
• Because of this Law, it is necessary to balance chemical equations
Balancing Chemical Equations
• In balanced chemical equations, each side of the equation has the same number of atoms of each element
• Coefficientsare used to balance chemical equations
Question
• What is the difference between a coefficient and subscript?
• Coefficients are written before the formulas
• Subscripts are part of the formula
• Never use SUBSCRIPTS to balance an equation!!
Rules for Balancing Equations
• 1. Determine the correct formulas for the reactants and products
• 2. Write the formulas for the reactants on the left side of the arrow. Write the formulas for the products on the right side of the arrow
Rules Continued
• 3. Count the number of atoms of each element present on both sides of the equation
• 4. Balance the elements one at a time by placing coefficients in front of the formula.
• 5. Check to make sure each atom is balanced
• 6. Check to make sure that all coefficients are in the lowest possible ratio
• **If no coefficient is written, the coefficient is assumed to be “1”
Examples
• Balance the following
• H2 (g) + O2 (g)  H2O (l)
• Na (s) + Br2 (g)  NaBr (aq)
• AgNO3 (aq) + Cu(s)  Cu(NO3)2 (aq) + Ag(s)
Classwork
• Complete Worksheet
Review-balance the following
• 1. Fe + O2  Fe2O3
• 2. Al2O3 + H2 Al + H2O
Quiz Review - Balance
• 1. FeCl3 + NaOH  Fe(OH)3 + NaCl
• 2. CuCl2 + NaI  CuI2 + NaCl
• 3. H2O2  H2O + O2
QUIZ
• 1) C6H6 + O2 CO2 + H2O
• 2) Mg + O2  MgO
QUIZ REVIEW
• 1. Solid sulfur reacts with gaseous fluorine to produce aqueous sulfur hexafluoride
• 2.Magnesium metal reacts with chlorine gas to make solid magnesium chloride
• Pb(NO3)2 + 2 NaOH  Pb(OH)2 + 2 NaNO3
• How many oxygen atoms are on the reactant side?
• How many oxygen atoms are in 2 NaNO3?
Balancing Equations -Determining Formulas
• To Balance Equations, you must remember how to write correct chemical formulas
Example
• Write the balanced equation for solid aluminum reacting with oxygen gas to form solid aluminum oxide
• **Remember that the diatomic elements (Mr. BrINClHOF) appear with a subscript of two when alone
• 1. Carbon reacts with Chlorine to form Carbon Tetrachloride
• 2. Magnesium metal reacts with solid Zinc (II) Carbonate to form solid Magnesium Carbonate and Zinc metal
• 3. Nitrogen gas reacts with Hydrogen gas to form Ammonia (NH3) gas
Types of Reactions
• There are five general types of reactions:
• Synthesis
• Decomposition
• Single Displacement
• Double Displacement
• Combustion
Synthesis Reactions
• Synthesis reactions are also called combination reactions
• A synthesis reaction occurs when two substances combine to form a new compound
Synthesis Reaction Continued
• The general form of a synthesis reaction is:
• A + X AX
• Substance “AX” is the only substance formed
Examples of Synthesis Reactions
• 2 Mg (s) + O2 (g)  2 MgO (s)
• Fe (s) + Cl2 (g)  FeCl2 (s)
• U (s) + 3 F2 (g)  UF6 (g)
Decomposition Reaction
• In decomposition reactions, one substance breaks down (decomposes) into two or more simpler substances
Decomposition Reactions Cont.
• General Form of Decomposition Reaction:
• AX A + X
Examples of Decomposition Reactions
• 2 HgO (s)  2 Hg (l) + O2 (g)
• Ca(OH)2  CaO (s) + H2O (g)
• H2SO4 (aq)  SO3 (g) + H2O (l)



Write Correct Balance Equations
• 1. The synthesis of KCl
• 2. The decomposition of magnesium oxide
• 3. The decomposition of hydrogen peroxide (H2O2) into oxygen and water
• 1. The synthesis of barium fluoride
• 2. The decomposition of Mg(OH)2 into magnesium oxide and water
• 3. The decomposition of water
Review-Write Balanced Equations
• 1. Gaseous hydrogen reacts with gaseous chlorine to form aqueous hydrogen chloride
• 2. Carbon monoxide gas reacts with gaseous oxygen to form solid carbon dioxide
Write balanced equations
• 1. The synthesis of Iron (III) oxide
• 2. The decomposition of cobalt (IV) oxide
• 3. The decomposition of calcium hydroxide into calcium oxide and water
Write Balanced Equations
• 1) Na + Cl2
• 2) HgCl2
• 3) Fe(OH)3
Single Replacement Reaction
• In a single replacement reaction (also called a displacement reaction), an element reacts with a compound
• A + BX AX + B
Examples of Single Replacement Reactions
• Mg + Zn(NO3)2  Mg(NO3)2 + Zn
• Mg + 2 AgNO3  Mg(NO3)2 (aq) + 2 Ag
Rules for Single Replacement Reactions
• Not all single replacement reactions occur
• You can determine if a reaction will occur by knowing the activity series of metals (See Handout)
Rules for Single Replacement
• The activity series tell you if one metal can replace another metal in a reaction
• The Activity Series is ordered
• Any metal that is above another metal in the activity series WILL REPLACE the less reactive metal
Li

K

Ca

Na

Mg

Al

Zn

Fe

Pb

H*

Cu

Hg

Ag

Activity Series
Predict if the following reactions will occur
• 1. Fe + H2O
• 2. Mg + LiNO3
• 3. Na + AgCl
Write balanced equations for the following reactions
• 1. Mg + O2
• 2. FeCl3
• 3. Fe + ZnO 
• 4. Br2 + MgI2 
Review
• Predict the products and balance:
• 1) Mg + O2
• 2) HCl 
• 3) Na + H2SO4 
• 4) Ag + ZnCl2 
Double Displacement Reactions
• In a double displacement reaction, two compounds react
• The compounds swap elements with each other
Double Displacement Cont
• Compounds contain a positive and negative part
• In a double displacement, the positive parts swap places with each other as do the negative parts
Examples
• PbCl2 (s) + Li2SO4 (aq)  PbSO4 (s) + 2 LiCl (aq)
• ZnBr2 (aq) + 2 AgNO3 (aq)  Zn(NO3)2 (aq) + 2 AgBr (s)
Predict the Products of the following reactions and balance
• BaCl2 (aq) + KClO3 (aq) 
• HCl (aq) + NaOH (aq) 
• RbBr (aq) + AgCl (aq) 
Combustion Reactions
• In a combustion reaction, a Hydrocarbon (compound containing Hydrogen and Carbon) reacts with Oxygen (O2)
• The products are CO2 and H2O
Example
• 2 C6H6 + 15 O212 CO2 + 6 H2O
• *Combustion Reactions commonly require large coefficients
Guided Practice
• Write the balanced equation for the following combustion reactions:
• a. C4H8
• b. C6H12O6
• c. C7H16
• 1. Hf + N2 (Hf takes a +4 charge)
• 2. Mg + H2SO4 
• 3. C2H6 + O2 
• 4. Pb(NO3)2 + NaI 
• 5. Fe + O2  (Fe takes a +3 charge)
Ionic Equations
• Most ionic compound dissociate (or break apart) when dissolved in water to form its component ions
• For example: NaCl (aq) really looks like Na+(aq) and Cl- (aq)
Soluble Vs. Precipitate
• Soluble means that the compound breaks down into its ions in water
• Ex) NaCl is soluble so it forms Na+ and Cl-
• Insoluble means that the compound doesn’t break down in water
Precipitate Reactions
• In double replacement reactions, often one of the product will be insoluble
• The insoluble product is referred to as a precipitate
• Precipitate Rules are on the EOC sheet
Practice
• Determine if soluble or insoluble:
• A) NaCl B) K2O
• C) Fe(NO3)3 D) AgCl
• E) BaS F) Cd(OH)2
• G) FeCl3 H) PbCO3
Ionic Equations Continued
• To write a Complete Ionic Equation:
• Write the aqueous substances as ions (leave any substances in gas, liquids, & solids alone)
• Example:
• AgNO3 (aq) + NaCl (aq)  AgCl (s) + NaNO3 (aq)
Writing Ionic Equations
• 1. (NH4)2S (aq) + Cd(NO3)2 (aq)  NH4NO3 (???) + CdS (???)
• 2. Zn(NO3)2 (aq) + (NH4)2S (aq)  ZnS (???) + NH4NO3 (???)
Spectator Ions
• Spectator Ions-Ions that are not directly involved in a reaction
• Spectator ions show up on both sides of the equation
• Spectator Ions cancel out
NET Ionic Equations
• Net Ionic Equation-Indicate the particles that actually take part in a reaction
• The Net Ionic Equation does NOT include spectator ions
• Net Ionic Equations must be balanced according to atoms and charge
Write Net Ionic Equations
• 1. (NH4)2S (aq) + Cd(NO3)2 (aq) 
• 2. Zn(NO3)2 (aq) + (NH4)2S (aq) 