Quarter test Thursday 4/7

1
4/4/11

• Quarter test Thursday 4/7
• What will be on this test?
• Redox,net ionic, emp formula, molecular form,
  comp, moles and molarity.
• Some stuff from throughout the first 3 quarters.
  Still only have 48 minutes

2
Emp. Formula

• 4/4/11
• A compound contains 25.9 nitrogen and 74.1
  oxygen. What is the empirical formula of the
  compound?
• Oh, and welcome back, hopefully refreshed and
  excited. 75 of this school year is over!!!

assume 100gram sample and convert to
grams convert to moles divide by smallest
moles make sure the ratios are whole numbers
3
Emp. Formula

• 4/4/11
• 25.9g N x 1 mole N/14 g N 1.85 mol N
• 74.1g O x 1mol O/16g O 4.63 mol O
• N1.85 O4.63 which is weird
• 1.85mol/1.85 1 4.63/1.85 2.50
• N1O2.5 still cant have fraction of atoms must
  be
• N2 O5

4
Molecular Formula

• Calculate the molecular formula of a compound
  whose molar mass is 60.0 g/mol and empirical
  formula is CH4N.

5
Molecular Formula

• Either same as Emp Formula or a simple whole
  number multiple of the EF
• Molar mass must be given to you, calculate efm.

Emp. Formula efm Molar mass/efm Molecular Formula
CH4N 30.0 60.0/30.0
C2H8N2
6
take this slow

• Warm-up 4/4/11
• What is the percent composition of Iron in Iron
  (II) carbonate?
• What is the empirical formula of a compound that
  is 54.1 Calcium, 43.2 Oxygen, and 2.7
  Hydrogen?
• YeeHaw!! Test Thursday! WHOOHOO!

7
Molecular Formula

• 4/4/11
• A compound is 75.46 carbon, 4.43 hydrogen, and
  20.10 oxygen by mass. It has a molecular weight
  of 318 g/mol. What is the molecular formula?

8
Molecular formula

• 75.46g/126.28
• 4.43g/1 4.43
• 20.10g/16 1.26
• Divide by smallest moles

4.98 or 5
/ 1.26
3.5
/ 1.26
/ 1.26
1
So Ratio is C5H3.5O1 Which is not whole
numbers
So multiply by 2 Empirical Formula is C10H7O2
9
Molecular formula

• So multiply by 2
• Empirical Formula is C10H7O2

Emp. Formula efm Molar mass/efm Molecular Formula
C10H7O2 159 318/159 Multiple of 2
C20H14O4
10
Homework

• 4/4/11
• Answer question 26-31 p 303 on notebook paper by
  tomorrow
• Read Section 16.2 p480 and take notes
• Answer questions 8,9 on p481
• Due tomorrow 10,11 on p 482

11
So quarter test, Huh!?

• Warm-up 4/5/11
• Predict product and write the net ionic equation
  for the following.
• MgS CuNO3 ? ?

Mg(NO3)2 Cu2S
(S) precipitate
Net Ionic Equation 1st Find the precipitate using
solubility rules
all Nitrates are soluble all Sulfides insoluble
except Group 12 and ammonium
12
Net ionic Review

• MgS(aq) 2CuNO3 (aq) ? Mg(NO3)2 (aq) Cu2S (s)

Break up all aqueous solutions, DO NOT break
apart the solid
Mg2 S-2 2Cu1 2NO31 ? Mg2 2NO31
Cu2S (s)
/
/
/
/
Net Ionic Equation S-2 2Cu1 ? Cu2S (s)
Must have charges.
Short cut What 2 ions make up the solid and
write
13
Daily EQWhat is molarity?
What is formula and Mass?

• 4/6/11 warm-up
• What is the mass of lithium dichromate needed to
  make 473 ml of a 2.5M solution?

Li2Cr2O7
229.8 g/mol
Must convert to liters .473 L
Substitute in equation 2.5M X .473L
Solve for X
X 229.8 g/mol
X 1.18 moles
271.2 grams
14
Molarity Lab

• 3/22/10
• Lets make a solution or 2.
• 1) With a partner, make 20 milliliters of a 2.0
  Molar solution of NaCl.
• 2)Next, make exactly 175 mL of a 0.147M solution
  of NaCl.
• 3) How much solution is created, if a 0.45M
  solution if we use 25.6 grams of sucrose (in
  yellow packet) to make the solution.
• Be sure to record the mass of salt used in each.
  Make this neat and easy for me to read/grade.

15
Molarity cont.

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