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Quarter test Thursday 4/7Quarter test Thursday 4/7 What will be on this test?What will be on this test? Redox,net ionic, emp formula, molecular Redox,net ionic, emp formula, molecular

form, % comp, moles and molarity.form, % comp, moles and molarity. Some stuff from throughout the first 3 Some stuff from throughout the first 3

quarters. Still only have 48 minutes quarters. Still only have 48 minutes

Emp. FormulaEmp. Formula4/4/114/4/11

A compound contains 25.9% nitrogen and A compound contains 25.9% nitrogen and 74.1% oxygen. What is the empirical 74.1% oxygen. What is the empirical formula of the compound?formula of the compound?

Oh, and welcome back, hopefully refreshed and Oh, and welcome back, hopefully refreshed and excited. 75% of this school year is over!!!excited. 75% of this school year is over!!!

assume 100gram sample and convert % to gramsassume 100gram sample and convert % to grams

convert to moles convert to moles

divide by smallest molesdivide by smallest moles

make sure the ratios are whole numbersmake sure the ratios are whole numbers

Emp. FormulaEmp. Formula

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25.9g N x 1 mole N/14 g N = 1.85 mol N25.9g N x 1 mole N/14 g N = 1.85 mol N

74.1g O x 1mol O/16g O = 4.63 mol O74.1g O x 1mol O/16g O = 4.63 mol O

NN1.851.85 O O4.63 4.63 which is weirdwhich is weird

1.85mol/1.85 =1 4.63/1.85 = 2.501.85mol/1.85 =1 4.63/1.85 = 2.50

NN11OO2.5 2.5 still can’t have fraction of atoms must bestill can’t have fraction of atoms must be

NN22 O O5 5

Molecular FormulaMolecular Formula

Calculate the molecular formula of a Calculate the molecular formula of a compound whose molar mass is 60.0 g/mol compound whose molar mass is 60.0 g/mol and empirical formula is CHand empirical formula is CH44N.N.


Either same as Emp Formula or a simple whole Either same as Emp Formula or a simple whole number multiple of the EFnumber multiple of the EF

Molar mass must be given to you, calculate efm.Molar mass must be given to you, calculate efm.

Emp. Emp. FormulaFormula

efmefm Molar Molar mass/efmmass/efm

Molecular Molecular FormulaFormula

CHCH44NN 30.030.0 60.0/30.060.0/30.0CC22HH88NN22

take this slowtake this slow

Warm-up 4/4/11Warm-up 4/4/11

What is the percent composition of Iron in What is the percent composition of Iron in Iron (II) carbonate?Iron (II) carbonate?

What is the empirical formula of a compound What is the empirical formula of a compound that is 54.1% Calcium, 43.2 % Oxygen, that is 54.1% Calcium, 43.2 % Oxygen, and 2.7% Hydrogen? and 2.7% Hydrogen?

YeeHaw!! Test Thursday! WHOOHOO!YeeHaw!! Test Thursday! WHOOHOO!


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A compound is 75.46% carbon, 4.43% A compound is 75.46% carbon, 4.43% hydrogen, and 20.10% oxygen by mass. It hydrogen, and 20.10% oxygen by mass. It has a molecular weight of 318 g/mol. has a molecular weight of 318 g/mol. What is the molecular formula?What is the molecular formula?

Molecular formulaMolecular formula

75.46g/12=6.28 75.46g/12=6.28

4.43g/1 = 4.434.43g/1 = 4.43

20.10g/16 = 1.2620.10g/16 = 1.26

Divide by smallest molesDivide by smallest moles

/ 1.26

/ 1.26

/ 1.26

= 4.98 or 5

= 3.5

= 1

So Ratio is C5H3.5O1 Which is not whole numbers

So multiply by 2

Empirical Formula is C10H7O2

Molecular formulaMolecular formula

So multiply by 2

Empirical Formula is C10H7O2

Emp. Emp. FormulaFormula

efmefm Molar Molar mass/efmmass/efm

Molecular Molecular FormulaFormula

C10H7O2 159159 318/159318/159

Multiple of 2Multiple of 2C20H14O4

HomeworkHomework

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Answer question 26-31 p 303 on notebook Answer question 26-31 p 303 on notebook paper by tomorrowpaper by tomorrow

Read Section 16.2 p480 and take notesRead Section 16.2 p480 and take notes

Answer questions 8,9 on p481Answer questions 8,9 on p481

Due tomorrow 10,11 on p 482Due tomorrow 10,11 on p 482

So quarter test, Huh!?So quarter test, Huh!?

Warm-up 4/5/11Warm-up 4/5/11

Predict product and write the net ionic Predict product and write the net ionic equation for the following.equation for the following.

MgS + CuNOMgS + CuNO3 3 ? ? Mg(NO3)2 + Cu2SNet Ionic Equation1st Find the precipitate using solubility rules

all Nitrates are solubleall Sulfides insoluble except Group 1&2 and ammonium

(S) precipitate

Net ionic ReviewNet ionic Review

MgSMgS(aq)(aq) + 2CuNO + 2CuNO3 (aq) 3 (aq) Mg(NOMg(NO33))2 2 (aq)(aq) + Cu + Cu22S S (s)(s)

Break up all aqueous solutions, DO NOT break apart the solid

Mg+2 + S-2 + 2Cu+1 + 2NO3–1 Mg+2 + 2NO3

–1 + CuCu22S S (s)(s)

Net Ionic Equation S-2 + 2Cu+1 CuCu22S S (s)(s)

Must have charges.

/ / / /

Short cut : What 2 ions make up the solid and writeShort cut : What 2 ions make up the solid and write

Daily EQ:What is molarity?Daily EQ:What is molarity?

4/6/11 warm-up4/6/11 warm-up

What is the mass of lithium dichromate What is the mass of lithium dichromate needed to make 473 ml of a 2.5M needed to make 473 ml of a 2.5M solution?solution? Must convert to liters .473 L

Substitute in equation 2.5M = X

.473L

Solve for X

What is formula and Mass?

Li2Cr2O7

X = 1.18 moles

229.8 g/mol

X 229.8 g/mol

271.2 grams

Molarity LabMolarity Lab3/22/103/22/10Let’s make a solution or 2.Let’s make a solution or 2.1) With a partner, make 20 milliliters of a 2.0 Molar 1) With a partner, make 20 milliliters of a 2.0 Molar

solution of NaCl.solution of NaCl.2)Next, make exactly 175 mL of a 0.147M solution 2)Next, make exactly 175 mL of a 0.147M solution

of NaCl.of NaCl.3) How much solution is created, if a 0.45M solution 3) How much solution is created, if a 0.45M solution

if we use 25.6 grams of sucrose (in yellow if we use 25.6 grams of sucrose (in yellow packet) to make the solution.packet) to make the solution.

Be sure to record the mass of salt used in each. Be sure to record the mass of salt used in each. Make this neat and easy for me to read/grade.Make this neat and easy for me to read/grade.

Molarity cont.Molarity cont.

4) Now actually do this. Dilute the 0.147M 4) Now actually do this. Dilute the 0.147M solution to a 0.08 M solution? How do you solution to a 0.08 M solution? How do you do this? What is new volume? How much do this? What is new volume? How much water?water?

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4/4/11