Exam 3 Ch.4 and Ch.5

f.)calcium phosphate

Ca3(PO4)2

Example Using Atomic Mass Units Calculate the mass (in amu) of 431 atoms of carbon. The mass of 1 carbon atom = 12.01 amu.

Calculate the mass (in amu) of 431 atoms of carbon. The mass of 1 carbon atom = 12.01 amu. -From Periodic Table Use the relationship as a conversion factor. 431 C atoms X (12.01 amu/ 1 C atoms) 5176

Balancing Chemical Equations (continued)

Chemists determine the identity of the reactants and products of a reaction by experimental observation. The identities (formulas) of the compounds must never be changed in balancing a chemical equation.

Examples for Type 2 Ionic Compounds

CuBr Copper(I) bromide FeS Iron(II) sulfide PbO2 Lead(IV) oxide

Molarity

Defined as the amount of solute, in moles, per liter of solution "M =" "n" /"V" where M is the molarity, n is the number of moles, and V is the volume of the solution in liters Usually when preparing a solution, we must weigh out the solute, so to calculate the concentration we must calculate the number of moles (this is why being able to switch from mass to moles is so important!)

VSEPR Theory

Electron groups around the central atom will be most stable when they are as far apart as possible-we call this valence shell electron pair repulsion theory -Since electrons are negatively charged, they should be most stable when they are separated as much as possible -Every group of electrons, whether in a bond or a lone pair, counts as a group. (Multiple bonds count as one group.) -There are five basic shapes in the VSEPR model, with some variations depending on how many charge clouds are in lone pairs vs. covalent bonds. -The resulting geometric arrangement will allow us to predict the shapes and bond angles in the molecule

Average Atomic Mass for Carbon

Even though natural carbon does not contain a single atom with mass 12.01 amu, for our purposes, we can consider carbon to be composed of only one type of atom with a mass of 12.01 amu. This enables us to count atoms of natural carbon by weighing a sample of carbon. To get the atomic mass of any element, refer to periodic table!

Solutions

Many chemical reactions take place in solutions -Remember that a solution is simply a homogeneous mixture Dissolving -The substance being dissolved is the solute -The substance doing the dissolving is the solvent -Usually, there is more solvent than solute -Water is no doubt the most familiar, but by no means the only solvent -When water is used, we are talking about aqueous solutions (aq)

Binary Ionic Compounds (Type II)

Metals in these compounds can form more than one type of positive charge. Charge on the metal ion must be specified. Roman numeral indicates the charge of the metal cation. Transition metal cations usually require a Roman numeral.

Prefixes used are

Mono- 1 Di- 2 Tri- 3 Tetra- 4 Penta- 5 Hexa- 6 Hepta- 7 Octa- 8

d.) dinitrogen tetroxide

N2O4

More polyatomic compound ions

NaOH Sodium hydroxide Mg(NO3)2 Magnesium nitrate (NH4)2SO4 Ammonium sulfate FePO4 Iron(III) phosphate

Another example of how to do it.

Name the compound PbS2. · Pb is the chemical symbol for lead. o Pb is not in the 1st or 2nd column; therefore a Roman numeral is needed. · S is sulfur, whose root is "sulf." Add the "ide" ending to get sulfide. · At this point we have lead (??) sulfide. · To find the Roman numeral... § S has a charge of -2. § There are 2 sulfur atoms so.... 2 x -2 = -4. <---- total negative charge § The total positive charge must be +4. § There is 1 lead atom so... +4 ÷ 1 = +4. The Roman numeral is IV. · Put the pieces together to get the name lead (IV) sulfide.

Count by weighing

Objects do not need to have identical masses to be counted by weighing. All we need to know is the average mass of the objects. To count the atoms in a sample of a given element by weighing we must know the mass of the sample and the average mass for that element.

Naming Compounds that Contain Polyatomic Ions

Polyatomic ions - ions that are made up of two Or more atoms covalently bound together You can have a molecule that consists of ions and covalently bonded atoms - the entire compound would be considered an ionic compound! They have special names that must be memorized

Combustion - rapid combination of oxygen with a substance.

Rapid combination of oxygen with a substance

A chemical reaction converts:

Reactants into products, reactants are transformed into different products

Write the formula of each of the following compounds: a.) Disulfur triiodide

S2I3

b.)Tin (IV) sulfate

Sn(SO4)2

Stoichiometry

Stoichiometry is the process of using a balanced chemical equation to determine the relative masses of reactants and products involved in a reaction.

Physical States- Physical states of compounds are often given in a chemical equation.

Symbol State (s) Solid (l) liquid (g) gas (aq) dissolved in water (in aqueous solution)

Mole Ratio

The mole ratio allows us to convert from moles of one substance in a balanced equation to moles of a second substance in the equation.

The Mole

The number equal to the number of carbon atoms in 12.01 grams of carbon. 1 mole of anything = 6.022 x 1023 units of that thing (Avogadro's number). 1 mole C = 6.022 x 1023 C atoms = 12.01 g C

Balancing Chemical Equations

The principle that lies at the heart of the balancing process is that atoms are conserved in a chemical reaction. Atoms are neither created nor destroyed. The same number of each type of atom is found among the reactants and among the products.

Binary Compounds

They are composed of two elements.

Solution Concentrations

We say that substances that dissolve are soluble, while those that do not are insoluble These terms are imprecise in that they do not tell how much will dissolve Two other terms that are rough estimates are dilute and concentrated -A dilute solution contains very little solute (think sugar in tea or coffee) -A concentrated solution contains a large amount of solute (think syrup) Again, however, these terms are imprecise in that they do not tell us how much is actually dissolved

Another example of a transition metal is

Write the formula for lead (IV) nitride. · The chemical symbol of lead is Pb. The oxidation state is +4. · Nitride is derived from nitrogen, whose symbol is N. Its oxidation state is -3. +4 -3 · So far we have Pb N. · The LCM of 4 and 3 is 12. We need three Pb atoms (+12 ÷ +4 = 3) and 4 N atoms (-12 ÷ -3 = 4) to balance the charges. · Putting it all together we have Pb3N4.

To go the other way around you have to

Write the formula for nickel (III) oxide. · The chemical symbol of nickel is Ni. The oxidation state is +3, as given by the Roman numeral. · Oxide is derived from oxygen, whose symbol is O. Its oxidation state is -2. +3 -2 · So far we have Ni O. · In order to balance the charges we find the least common multiple (LCM) of 3 and 2. The LCM is 6. We need two Ni atoms (+6 ÷ +3 = 2) and three O atoms (-6 ÷ -2 = 3) to balance the charges. · Putting it all together we have Ni2O3.

What is the chemical formula of ammonium sulfate? a.) (NH4)2SO4 b.) NH4+SO4- c.) NH4SO4 d.) NH4(SO4)2 e.) (NH4)3(SO4)2

a.) (NH4)2SO4

What is a clue that a chemical reaction has occurred? "Colorless hydrochloric acid is added to a red solution of cobalt(II) nitrate, turning the solution blue." a) The color changes. b) A solid forms. c) Bubbles are present. d) A flame is produced

a.) the color changes

What is the name of the compound KClO3? a) potassium chlorite b) potassium chlorate c) potassium perchlorate d) potassium carbonate

b) potassium chlorate

Covalent Compound Exercise What is the name of the compound SeO2? a) selenium oxide b) selenium dioxide c) selenium(II) oxide d) selenium(IV) dioxide

b) selenium dioxide

Balance the following equation in standard form (lowest multiple integers) and determine the coefficient on FeO. ?FeO(s) + O2(g)-------> Fe2O3(s) a) 3 b) 4 c) 2 d) 1

b.) 4

What is a clue that a chemical reaction has occurred? "A solid forms when a solution of potassium iodide is added to a solution of lead (II) nitrate." (slide 11) a) A gas forms. b) A solid forms. c) Bubbles are present. d) A flame is produced.

b.) A solid forms

When balancing a chemical equation, which of the following statements is false? a) Subscripts in the reactants must be conserved in the products. b) Coefficients are used to balance the atoms on both sides. c) When one coefficient is doubled, the rest of the coefficients in the balanced equation must also be doubled. d) Phases are often shown for each compound but are not critical to balancing an equation

c) When one coefficient is doubled, the rest of the coefficients in the balanced equation must also be doubled.

What is a clue that a chemical reaction has occurred? (ch.5 slide 9) a) The color changes. b) A solid forms. c) Bubbles are present. d) A flame is produced.

c. ) bubbles are present

Consider the burning of charcoal (carbon):

carbon + oxygen -------> carbon dioxide C + O2 -------->CO2 C(s) + O2(g) ---------> CO2(g) law of conservation of matter or mass

When blue light shines on a mixture of hydrogen and chlorine gas, the elements react explosively to form gaseous hydrochloric acid. What is the unbalanced equation for this process? a) H2(g) + CH4(g) HCl(g) b) HCl(g) H(g) + Cl(g) c) H(g) + Cl(g) HCl(g) d) H2(g) + Cl2(g) HCl(g)

d) H2(g) + Cl2(g) HCl(g)

Ionic Compound Exercise What is the name of the compound SrBr2? a) strontium bromine b) sulfur bromide c) strontium dibromide d) strontium bromide

d.) strontium bromide

What is the chemical formula of sodium bicarbonate? a.) Na2CO3 b.) Na(CO3)2 c.) Na4(CO3)2 d.) Na(HCO3)2 e.) NaHCO3

e.) NaHCO3

How to Write and Balance Equations

1.) Read the description of the chemical reaction. What are the reactants, the products, and their states? Write the appropriate formulas. Hydrogen gas (H2) and oxygen gas (O2) combine to form liquid water (H2O). 2.) Write the unbalanced equation that summarizes the information from step 1. H2(g) + O2(g) H2O(l) 3.) Balance the equation by inspection, starting with the most complicated molecule. We must balance the equation by adding more molecules of reactants and/or products Equation is unbalanced - count the atoms on both sides of the arrow. H2(g) + O2(g)----------> H2O (l) 4.) Check to see that the coefficients used give the same number of each type of atom on both sides of the arrow. Also check to see that the coefficients used are the smallest integers that give the balanced equation. The balanced equation is: 2H2(g) + O2(g)-----> 2H2O(l) or could be: 4H2(g) + 2O2(g) 4H2O(l)

Some clues that a chemical reaction has occurred:

- The color changes - A solid forms - Bubbles form - Heat and/or a flame is produced, or heat is absorbed -Formation of water -Formation of Gas - Transfer of electrons - Formation of a solid

What is the coefficient in front of N2 when the chemical equation below is balanced in standard form (lowest multiple integers)? N2 + H2 -------> NH3 1 2 3 4

1

Rules for Naming Type I Ionic Compounds

1. The cation is always named first and the anion second. 2. A simple cation takes its name from the name of the element. 3. A simple anion is named by taking the first part of the element name (the root) and adding -ide.

Mass CalculationsSteps for Calculating the Masses of Reactants and Products in Chemical Reactions

1.) Balance the equation for the reaction. 2.) Convert the masses of reactants or products to moles. 3.) Use the balanced equation to set up the appropriate mole ratio(s). 4.) Use the mole ratio(s) to calculate the number of moles of the desired reactant or product. 5.) Convert from moles back to masses

The fuel in small portable lighters is butane (C4H10). The coefficient in front of oxygen when the reaction below is balanced in standard form (lowest multiple integers) is C4H10 + O2 CO2 + H2O 3 6 13 15

13

What does a balanced chemical equation tell us? -How many atoms, compounds, ions, and/or molecules that are involved in a reaction (Also Volumes) -Ratio of the different atoms, compounds, ions, and/or molecules to each other -Moles of each of the components that are involved in a reaction

2H2(g) + O2(g) -----> 2H2O(l)

Mole Ratio Example: Consider the following balanced equation: Na2SiF6(s) + 4Na(s) → Si(s) + 6NaF(s) How many moles of NaF will be produced if 3.50 moles of Na is reacted with excess Na2SiF6? Where are we going? We want to determine the number of moles of NaF produced by Na with excess Na2SiF6. What do we know? The balanced equation. We start with 3.50 mol Na.

3.50 mol Na X (6 mol NaF/4 mol Na)= 5.25 mol NaF (Starting (mole ratio) amount)

How do we get there?

4Cr(s) + 3O2(g) → 2Cr2O3(s) Convert moles of Cr2O3 to grams of Cr2O3. 0.144 mol Cr2O3 X (152.00 g Cr2O3/ 1 mol Cr2O3)= 21.9 g Cr2O3 Conversion string: 15.0 g CrX (1 mol Cr/ 52.00 g Cr) X (2 mol Cr2O3/ 4 mol Cr) X (152.00 g Cr2O3/ 1mol Cr2O3)= 21.9 g Cr2O3

How do we get there? 4Cr(s) + 3O2(g) → 2Cr2O3(s)

4Cr(s) + 3O2(g) → 2Cr2O3(s) Convert the mass of Cr to moles of Cr. 15.0 g Cr X (1 mol Cr/ 52.00 g Cr)= 0.288 mol Cr Determine the moles of Cr2O3 produced by using the mole ratio from the balanced equation. 0.288 mol Cr X (2 mol Cr2O3/ 4 mol Cr)= 0.144 mol Cr2O3

Calculate the mass (in amu) of 75 atoms of aluminum.

75 atoms Al X (26.98 amu/ 1 Al atom)= 2,023.5

Information Given by Chemical Equations

A balanced chemical equation gives relative numbers (or moles) of reactant and product molecules that participate in a chemical reaction. The coefficients of a balanced equation give the relative numbers of molecules.

Chemical reactions involve a rearrangement of the ways atoms are grouped together.

A chemical equation represents a chemical reaction. -Reactants are shown to the left of the arrow. -Products are shown to the right of the arrow. Methane Oxygen Carbon Dioxide Water CH4 + O2 -----> CO2 + H2O

The Mole

A sample of an element with a mass equal to that element's average atomic mass (expressed in g) contains one mole of atoms (6.022 × 1023 atoms). Comparison of 1-Mol Samples of Various Elements

Molar Mass- Mass of one mole of a compound

Add up the Atomic Masses from periodic table Mass in grams of one mole of the substance: Molar Mass of N = 14.01 g/mol Molar Mass of H2O = 18.02 g/mol (2 × 1.008 g) + 16.00 g Molar Mass of Ba(NO3)2 = 261.35 g/mol 137.33 g + (2 × 14.01 g) + (6 × 16.00 g)

Examples of Ionic Compounds

AlCl3 Al(3+) Cl(-) KCl K(+) Cl(-) MgBr2 Mg(2+) Br(-) CaO Ca(2+) O(2-)

In a chemical reaction atoms are not created or destroyed

All atoms present in the reactants must be accounted for in the products. Same number of each type of atom on both sides of the arrow.

Type I Ionic Compounds

Are composed of Groups 1A, 2A, and 3A metals and a nonmetal. Metals present forms only one cation.

Type II Ionic Compounds

Are composed of transition metals and nonmetal. Metals present can form 2 or more cations with different charges.

Binary Ionic Compounds

Are composed of two elements. A metal and a nonmetal. They contain positive cations (metals) and negative anions (nonmetals). Metals lose electrons while nonmetals gain electrons.

Binary Covalent Compounds

Are composed of two elements. A nonmetal and a nonmetal. They share pairs of electrons.

Atomic Masses, counting atoms by weighing

Atoms have very tiny masses so scientists made a unit to avoid using very small numbers. 1 atomic mass unit (amu) = 1.66 X 10^-24 g The average atomic mass for an element is the weighted average of the masses of all the isotopes of an element.

One of the major problems with burning coal as a fuel is that it pollutes the air with sulfur dioxide, nitrogen oxides, and soot, all of which contribute to acid rain and cause respiratory distress. Technologies that can convert coal to cleaner burning fuels are being developed. One possibility is "hydrogasification." Write the unbalanced equation for this process, which involves the chemical reaction of the carbon in coal with hydrogen gas to yield gaseous CH4 (methane). C2(s) + H2(g) --------> CH4(g) CH4(g) -------> C(s) + H(g) C(s) + H2(g) ------> CH4(g) C(s) + H(g) -----> CH4(g)

C(s)+ H2(g)--------> CH4 (g) Balanced equation C(s) + 2H2(g)-------> CH4 (g)

c.)Iodine pentachloride

IF5

Of the three that are correct, which one is preferred most (the most accepted convention)? Why? CaO + C-----> CaC2 + CO2 I. CaO2 + 3C----> CaC2 + CO2 II. 2CaO + 5C---> 2CaC2 + CO2 III. CaO + (2.5)C---> CaC2 + (0.5)CO2 IV. 4CaO + 10C---> 4CaC2 + 2CO2

II

Which of the following correctly balances the chemical equation given below? There may be more than one correct balanced equation. If a balanced equation is incorrect, explain what is incorrect about it. CaO + C-----> CaC2 + CO2 I. CaO2 + 3C ---->CaC2 + CO2 II. 2CaO + 5C---> 2CaC2 + CO2 III. CaO + (2.5)C--->CaC2 +(0.5)CO2 IV. 4CaO + 10C -----> 4CaC2 + 2CO2

II, III, and IV are correct

Law of conservation of matter or mass:

In a reaction, matter and mass are always conserved

To find out what the roman numeral is, you first have to find the charge for the anion (nonmetal). With this you can find the numeral for the transition metal.

Ex. Name the compound FeCl2. · Fe is the chemical symbol for iron. Fe is not in the 1st or 2nd column; therefore a Roman numeral is needed in the name. We'll come back to that shortly. · Cl is the chemical symbol for chlorine, whose root is "chlor." Add the "ide" ending to get chloride. · At this point we have iron (??) chloride. · To find the Roman numeral... Find the charge of the anion. Cl has a -1 charge. Multiply times the number of those atoms to get the total negative charge. There are 2 Cl atoms. 2 times -1 = -2. <--- total negative charge. Balance total negative charge with total positive charge. The total negative charge of -2 must be balanced with a total positive charge of +2. Divide the total positive charge by the number of atoms to get Roman numeral. There is only 1 Fe +2 divided by 1 = +2. The Roman numeral is II. · Put the pieces together to get the name iron (II) chloride.

Naming ionic compounds containing polyatomic ions follows rules similar to those for binary compounds.

Example: Ammonium Acetate NH4\C2H3O2 (NH4)+ (C2H3O2)-

Naming polyatomic ionic compounds is also easy- Name the cation first, followed by the anion second.

Example: Mg(OH)2 Mg+2 is the cation, OH- is the anion magnesium hydroxide Example: NH4Br NH4+ is the cation, Br- is the anion ammonium bromide

Binary Covalent Compounds (Type III) Examples:

Examples: CO2 Carbon dioxide SF6 Sulfur hexafluoride N2O4 Dinitrogen tetroxide

Electronegativity: How strongly elements attract electrons in a chemical bond. Electronegativity increases up the periodic table and to the right. Some atoms tend to "hog" electrons in a chemical bond. This has important consequences on how the overall molecule behaves. Large difference in electronegativity can lead to molecules being polar (Think magnet)

Examples: Water, HCl, CN

e.) Iron(III) nitrite

Fe(NO2)3

Percent Concentrations (JUST AN FYI)

For many practical applications, such as those in medicine and pharmacy, solution concentrations are often expressed as percentages Depending on whether we are working with a solid or a liquid, we can express this percentage by mass (for a solid) or by volume (for a liquid) "% by mass = " "mass of solute" /"mass of solution" ×100"%" "% by volume = " "volume of solute" /"volume of solution" ×100"%"

Stoichiometry Example

For the following unbalanced equation: Cr(s) + O2(g) → Cr2O3(s) How many grams of chromium(III) oxide can be produced from 15.0 g of solid chromium and excess oxygen gas? Where are we going? We want to determine the mass of Cr2O3 produced by Cr with excess O2. What do we know? The unbalanced equation. We start with 15.0 g Cr. We know the atomic masses of chromium (52.00 g/mol) and oxygen (16.00 g/mol) from the periodic table. What do we need to know? We need to know the balanced equation. 4Cr(s) + 3O2(g) → 2Cr2O3(s) We need the molar mass of Cr2O3. 152.00 g/mol

Rules for Naming Type III Binary Compounds (Covalent Bonds)

Formed between two nonmetals 1. The first element in the formula is named first, and the full element name is used. 2. The second element is named as though it were an anion. 3. Prefixes are used to denote the numbers of atoms present. 4. The prefix mono- is never used for naming the first element.