Topic 2: Formulas and Equations Chemical Symbols - Each element has a one, two or three letter symbol to represent it - Symbols with more than one letter are always written capital letter then lower case letter - Based on IUPAC system of naming Diatomic molecules - elements found only combined covalently in nature H2, N2, O2, F2, Cl2, Br2, I2

Element vs. Compound Element - Atoms of all the same type Cannot be chemically broken down into two different substances. Na Cu Compound Combination of elements NaCl CuSO4 a. All sample of a compound have the same properties b. Atoms in a compound are in a simple ratio c. All areas of a compound are the same

What two elements do you think are found in a quarter? What’s in a Quarter? What two elements do you think are found in a quarter? (Write the name an symbol below. What do you think will happen when the RED HOT quarter is placed into the beaker of methanol? Describe what did happen?   Materials: 19.4 MB US quarter (pre-2000) methanol 100 mL beaker, 150 mL watch glass (to cover propane or butane torch, or Bunsen burner tongs Procedure: Use a torch or hot Bunsen burner to heat the quarter very hot. It needs to be as red-hot as possible. When peak temperature has been reached, immediately drop the red-hot quarter into a 150 mL beaker containing 100 mL of methanol. If the methanol ignites when the coin is dropped in, cover it with the watch glass to extinguish the flames. As soon as the quarter is dropped in it will boil the methanol. In a few moments the methanol will stop bubbling. A short time later a phase transition takes place which will release heat. Another rush of bubbles will be seen as more methanol boils. The quarter will grow pink as a layer of copper migrates up through the nickel coating. Is the reaction that took place exo or endothermic/ Why did the quarter change color?

Chemical Formulas Chemical formulas tell us two things Type of elements present Number of atoms Subscript- Indicates number of atoms Examples MgBr2 1 Mg for every 2 bromines Al2O3 2 aluminums for every 3 oxygens Ca(OH)2 1 calcium , 2 hydrogens and 2 oxygens 2 sets of OH Example - How many sulfur atoms are present in Pb(SO4)2? 2 How many oxygen atoms are present? 4 x 2 = 8

Coefficients -numbers placed in front of a chemical formula to indicate how many molecules are present MgS Ex. MgS 6 MgS MgS MgS MgS MgS

What is the total number of molecules in this equation? Burning Money!!!! Examine the following equation and answer the questions that follow 2 C3H7OH(l) + 9 O2(g) → 6 CO2(g) + 8 H2O(g) ∆Hrxn = -1987 kJ/mol What is the total number of molecules in this equation? How many atoms of oxygen are in the equation? 55ml isopropyl alcohol mixed with 45 ml water. United States currency is not “paper” money; rather, it is manufactured from cotton. The cotton fibers preferentially absorb the water in the solution mixture, which prevents it from being burned. However, the flame must be put out as the flames subside in order to prevent the water from evaporating and burning the bill. The water in the mixture also acts to absorb some of the energy from the reaction Describe the reaction as either exothermic or endothermic.

- Water gets trapped in the crystal structure of some ionic compounds Hydrates - Water gets trapped in the crystal structure of some ionic compounds The same amount of water is found in the crystal all the time Ex. CuSO4* 5H2O * Does not mean multiply!!! It means it is an hydrate!

Types of Chemical Formulas Molecular Formula Tells us how many atoms of each element are needed to form the molecule Examples C2H6 -ethane - 2 C : 6H Empirical Formula Shows the simplest ratio of atoms C2H6 CH3 Molecular Empirical C3H6 CH2 Sometimes the empirical formula and the molecular formula are the same CO2 H2O

Which of the following are empirical formulas? A. H2O2 B. CO C. P2O4 D. Al2O3 What is the empirical formula of the following? C6H12O6 Hg2O4 PbSO4 PbSO4 CH2O HgO2

Writing Chemical Formulas When Ba is combined with Cl, is the formula BaCl? Or ClBa? Or Cl2Ba? Or Ba2Cl? Based on OXIDATION NUMBERS

Oxidation numbers - Indicate the number of electrons lost or gained in a bond Oxidation number Negative oxidation number Atom gains partial or total control of electrons Positive oxidation number Atom loses partial or total control of electrons

Rules for Writing Formulas The element or ion with the positive oxidation state (the metal) is written first Write in the oxidation states, then write out who comes first. Mg Br +2 -1 -1 +2 Ca Cl -2 +? Cu O +1 -2 Li S

Add one more Cl-1 to get to zero +1 -2 H2O H O Li S +1 -2 Li2S 2. The oxidation states of all elements in a compound must add up to zero -For every electron lost, it must be gained by another atom Example Cl -1 -1 +2 Ca Cl CaCl2 Loses control of 2 e- Gains control of 1e- 2 e- Add one more Cl-1 to get to zero +1 -2 H2O H O Li S +1 -2 Li2S 3. Polyatomic ions are treated as one element +2 -2 Ca SO4 Na PO4 CaSO4 +1 -3 Na3PO4

4. If a polyatomic ion is used more than once, put parentheses around it +2 -1 Ca(OH)2 Ca OH NH4 SO3 +1 -2 (NH4)2SO3 Practice Li+1 O-2 Li2O Lithium oxide Magnesium iodide potassium phosphate ammonium nitrate aluminum oxide calcium phosphate Mg+2 I- MgI2 K+1 PO4-3 K3PO4 NH4+ NO3- NH4NO3 Al2O3 Al+3 O-2 Ca3(PO4)2 Ca+2 PO4-3

Nomenclature Naming compounds 1. Binary Compound Consists of 2 different elements To name these, use the name of the first atom, remove “ine” from the second atom and add “IDE” NaCl Na__________ Cl_________ NaCl _____________________

You must know the –ide names for the following Hydrogen Hydride Oxygen Oxide Bromine Bromide Iodine Iodide Fluorine Flouride Nitrogen Nitride Selenium Selenide Sulfur Sulfide

Examples MgBr2 LiO SrO AlI3 NaF ZnS Magnesium bromide Magnesium bromine Lithium oxide Strontium oxygen Strontium oxide Aluminum iodide Sodium fluoride Zinc sulfide 2. Ternary compounds Compounds with 3 or more elements -usually a metal with a POLYATOMIC ION

Polyatomic ion Group of atoms bonded together to obtain an overall charge Has special properties unlike the individual atoms -3 O | O - P - O Often acts as one atom Found on Table E PO4-3 phosphate Name the following polyatomic ions NH4+ SO3-2 OH- CO3-2 sulfite hydroxide carbonate ammonium Polyatomic ions bond IONICALLY with other ions

Naming compounds with polyatomic ions - Do not change any parts, take the name of each part of the compound -Circle the polyatomic ion in each compound, then name the compound MgSO4 NaSCN LiOH NH4OH CaCO3 Li2SO3 Al(OH)3 Magnesium sulfate Sodium thiocyanate Lithium hydroxide Ammonium hydroxide Calcium carbonate Lithium sulfite Aluminum hydroxide

Naming Covalent Compounds -compounds with only nonmetals -using Table S, write the name of the element with the lower electronegativity first -use prefixes to tell how many of each element are present Ex. CO2 Carbon dioxide 2.6 3.4 2 oxygen's N2Cl2 Dinitrogen dichloride 3.0 3.2

Try: Carbon tetrachloride Diphosphorous pentoxide

Name the following Compounds LiBr MgSO4 CaCO3 SrCrO4 ZnS Al2(SO4)3 NH4NO3 Write the empirical formula C6H12O6 P2O4 C2H2 PbCl4 H2O2

Write out the following formulas Calcium oxide Lithium Sulfide Lithium Sulfate Magnesium phosphate Aluminum carbonate Nitrogen dioxide

STOCK SYSTEM So far, we have learned how to take different elements and combine them together to make a compound. But there are some elements that have several oxidation states. For example, what is the formula for lead oxide? Pb has two oxidation states Pb+2 and Pb +4 Pb+2 O-2 Pb+4 O-2 O-2 PbO PbO2 Which of the two is correct? BOTH are correct! How can we have two different formulas with the same name? We need a way to distinguish between these two.

Stock System CuO MgO LiNO3 NO CaSO4 Ni(NO3)2 ZnCO3 NO NO Yes NO Yes NO - used when the first part of a compound (the positive one) has two or more positive oxidation states. Which of the following requires the stock system? CuO MgO LiNO3 NO CaSO4 Ni(NO3)2 ZnCO3 NO NO Yes NO Yes NO Yes

How is the stock system used? 1. Assign oxidation numbers to the elements in the compound 2. Write the oxidation state of first element as a roman numeral Pb+4 O-2 Pb+2 O-2 O-2 PbO PbO2 Pb is in the +2 state, so it is called Pb is in the +4; state, so it is called Lead (II) oxide Lead (IV) oxide +2 -1 SnCl2 Sn has an oxidation state of +2 or +4. +2 -2 = 0 The Cl must be in the -1 state, since Sn must be a positive oxidation state, Since there are two Cl’s, the Sn must be in the +2 oxidation state to cancel out the Cl’s Tin (II) Chloride

Practice - All of the following compounds need the stock system Practice - All of the following compounds need the stock system. Determine the oxidation state of the cation (the first ion) and write out the name. +1 -1 Copper (I) nitrate CuNO3 NiF2 HgO Hg2O FeCl3 NO2 +2 -1 Nickel (II) fluoride +2 -2 +2 -2 Mercury (II) oxide +1 -2 Mercury (I) oxide +2 -2 +3 -1 Iron (III) chloride +3 -3 +4 -2 Nitrogen (IV) oxide +4 -4

Writing Formulas with the Stock System If we are given a chemical name that uses the stock system, how do we write the formula? Example - What is the chemical formula for Copper (II) oxide? We know that the compound contains copper and oxygen And we know that oxygen must take a -2 oxidation state +2 -2 O Cu Don’t have to look up copper. The (II) tells us that it is in the +2 state

CuO What is the chemical formula for copper (II) oxide? What is the formula for Nickel (III) sulfate? +3 -2 According to chart E! Ni SO4 Ni (SO4) 2 3

Now write out the formulas for the following. Nitrogen (II) chloride Iron (III) oxide Lead (IV) carbonate Copper (I) sulfate N+2 Cl-1 NCl2 Fe+3 O-2 Fe2O3 Pb+4 CO3-2 Pb(CO3)2 Cu+1 SO4-2 Cu2SO4

__Chemical Equations - Shows what happens during a chemical reaction The chemicals involved How many of each molecule Energy used, phases Reactants Substances that exist before the reaction takes place Always found on the left, or facing away from the arrow Products Substances that exist after a chemical reaction Always found on the right, or facing the arrow head The reaction arrow is the “ “. It is always found in the middle of a chemical reaction and it divides up the reactants and the products

Examples - List the reactant and the products of the following reactions Reactants Products 2 H2 O2 2 H2O a. 2 H2 + O2 2 H2O HCl NaOH NaCl H2O b. HCl + NaOH H2O + NaCl

? Balancing a chemical equation CO + O2 CO2 How many carbon atoms are on each side of the equation? 1 How many oxygens are on each side of the equation? Three on the reactants, but only 2 one the products side Is this possible? ? No, something must happen to the other oxygen O = C=O O = O O O O

We need another CO for the other oxygen to attach to. = C=O O = So two molecules of CO combine with one molecule of O2 O O O O O O O = C=O 2 CO + O2 2 CO2 O O 2 C 4 O 2 C 4 O Now the equation is balanced because we have the same number and types of atoms on both sides

Step 1: Write the word equation Problem 1: Write the balanced equation for the reaction between aluminum sulfate and calcium chloride to produce aluminum chloride and a white precipitate of calcium sulfate. Step 1: Write the word equation Aluminum sulfate + Calcium chloride  Aluminum chloride + Calcium Sulfate Step 2: Replace the words with the correct formulas Al2(SO4)3 CaCl2 AlCl3 CaSO4 +  + Step 3: Adjust coefficients to make the equation balance. Use trial and error until both sides have same number of each element. Al2(SO4)3 + CaCl2  AlCl3 + CaSO4

This is a hit and miss procedure This is a hit and miss procedure. Often you will need to change the coefficients several times in order to balance the equation correctly Remember to only change the coefficients, not the molecular formula Examples 2 3 a. ____ NH3 _____ N2 + ____ H2 b. ____ Li2SO4 + ____ Na ____ Na2SO4 + ____ Li c. ____ HCl + ____ Mg ____MgCl2 + _____ H2 2 2 2

Important point -Some pure elements must exist as DIATOMIC molecules H Pure hydrogen gas is H2 N Pure nitrogen is N2 This occurs for the following elements H, N, O, F, Cl, Br, I Example - Balance the following equation Nitrogen + oxygen nitrogen (II) oxide N2 + O2 2 NO

Showing Energy changes in Reactions A. Reactions that require energy are endothermic Ex. 2 H2O + energy  2 H2 + O2 B. Reactions that give off energy are exothermic Ex. 2 H2 + O2  2 H2O + energy

Write the formulas for the following compounds Match-Making The first matches were invented in 1827 by chemist John Walker. He determined that a wood splint tipped with antimony (II) sulfide, potassium chlorate, gum and starch could be ignited by striking it against a rough surface. Write the formulas for the following compounds Antimony (II) sulfide Potassium chlorate Describe the reaction that took place when Mr. Stone lite the mixture on fire. Materials: potassium chlorate, KClO3, 0.5 g sulfur powder, 0.5 g fireproof lab mat or board barbeque lighter evaporating dish Procedure: Carefully crush the potassium chlorate into a fine powder. Place it into the evaporating dish and add the sulfur powder. Gently stir the mixture in the evaporating dish until homogeneous. Pour the mixture onto the lab mat and shape into a thin line. Ignite with the barbeque lighter held at arms length. Was the reaction exo or endothermic and explain why. Why safety matches? Combustible materials are separated between match and striking surface

Balance the following equations _____ KNO3 + _____ Na2SO4  _____ K2SO4 + _____ NaNO3 _____ H2 + _____ Cl2  _____ HCl _____ Li + _____ O2  _____ Li2O _____ HgO  _____ Hg + _____ O2 _____ AlBr3 + _____ Cl2  _____ AlCl3 + _____ Br2

Nitrogen + oxygen  nitrogen(IV) oxide Barium chloride + sodium sulfate  barium sulfate + sodium chloride Magnesium + sulfuric acid  magnesium sulfate + hydrogen gas Potassium + water  potassium hydroxide + hydrogen gas Aluminum + hydrochloric acid  aluminum chloride + hydrogen gas

Types of Chemical Reactions There are four basic types of chemical reactions Observe the products and the reactants to determine the type of reaction. A. Synthesis Two or more compounds combine together to produce one compound Ex. A + B --> AB Examples 2 H2 + O2 --> 2 H2O 2 Mg + O2 --> 2 MgO

Exothermic reaction of Calcium oxide and water

B. Decomposition Single compound breaks down into 2 or more compounds AB --> A + B Examples 2 H2O --> 2 H2 + O2 2 NaCl --> 2 Na + Cl2 C. Single Replacement Element + Ionic Compound Element + Ionic Compound X + AB  A + XB Ex. Zn + CuSO4  ZnSO4 + Cu

What does an elephant use to clean it’s teeth? Elephant toothpaste Balance the equation below H2O2(aq) → H2O(g) + O2(g) + energy What if the name of the H2O2 (you’ll need to use table E) We’ve talked of many types of reactions at this point. Use to types that we’ve talked about during this unit to describe the reaction above. Materials: hydrogen peroxide, H2O2, 30% 20 mL dishwashing soap, 10 mL sodium iodide solution, NaI, 2M, 5 mL graduated cylinder 100 mL graduated cylinder 10 mL spill tray wooden matches   Procedure: pour 20 mL of 30% hydrogen peroxide into the 100 mL graduated cylinder. Use gloves and safety glasses as the peroxide is corrosive to skin and can cause burns. Add 10 mL of dishwashing soap to the graduated cylinder. When ready for the presentation, place the graduated cylinder in the spill tray. Point out to the audience that hydrogen peroxide will slowly decompose on its own, although the rate is very slow, as can by seen by the lack of bubbles in the graduated cylinder. Add the 5 mL sodium iodide solution. Within 5 to 10 seconds a large column of foam will rapidly rise up the graduate and erupt out of the cylinder. Steam and heat will also be produced. The foam contains a lot of oxygen which can be illustrated by pushing a burning match into the foam. Instead of going out, the flame grows larger. Discussion: The catalytic decomposition of hydrogen peroxide is exothermic, as can be seen from the steam. The catalyst acting in this reaction is the iodine ion, which is not changed or used up in the reaction: I - (aq) 2 H2O2(aq) → 2 H2O(g) + O2(g) + energy It is the oxygen gas and water vapor that cause the dishwashing soap to foam up.

D. Double Replacement 2 compounds in solution are mixed C C C Ex. AB + CD --> CB + AD C A B C A D A A A Watch the oxidation states when making new compounds! NaCl(aq) + AgNO3(aq) NaNO3(aq) + AgCl(s) Al(OH)3 + NaI 3 AlI3 + NaOH 3

Synthesis reaction – fog machine Synthsis pg 113 Pg 117 synthesis Single and double replacement 123 Elephant toothpaste decomp

Unknown Reactants and Products -since matter can NOT be created or destroyed, you must always have the same number of each type of element on each side of the equation -if you have a balanced equation you should be able to figure out what the unknown product or reactant is EX. H2SO4 + 2 NaOH  Na2SO4 + WHAT? BaCl2 + K2CO3  WHAT? + BaCO3 2 NaHCO3  Na2CO3 + H2O + WHAT?

Determining Missing Mass in an Equation RULE: Total mass of reactants = total mass of products If 103.0g of KClO3 are decomposed to form 62.7 g of KCl and O2 gas according to the equation 2 KClO3  2 KCl + 3 O2 How many grams of oxygen are formed? Total mass of reactants = 103.0 g Total mass of products = 103.0 g 103.0 = mass of O2 + 62.7 g KCl 103.0 – 62.7g KCl = mass of O2

How many grams of silver nitrate are needed to react with 156 How many grams of silver nitrate are needed to react with 156.2g sodium sulfide to produce 595.8 g silver sulfide and 340.0 g sodium nitrate? 1. Rewrite and balance the equation. 2. Substitute masses in and solve for missing mass