based on data Usually composition data Why is it important to be able to calculate the empirical formula Penicillin Antibiotic Discovered about 80 years ago Paved the way for other antibiotics to be created which increased life expectancy ID: 310422
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Slide1
Empirical Formula
= based on data
Usually % composition dataSlide2
Why is it important to be able to calculate the empirical formula?
Penicillin
Antibiotic
Discovered about 80 years ago
Paved the way for other antibiotics to be created which increased life expectancySlide3
Why is it important to calculate the empirical formula?
How was penicillin discovered?By accident!
In 1928, Alexander Fleming was working at the University of London with a common bacterium that causes boils and other infections such as blood poisoning.
The bacteria being grown was contaminated by a bluish-green mold.Slide4Slide5Slide6
Penicllin
Cryosogenum
This photomicrograph shows the rod and pencil-shaped branches. The name comes from the Latin
penicillus
which means paintbrush.Slide7
Isolating pure Penicillin
1940: 2 chemists at Oxford University (Howard Florey and Ernst Chain) were able to isolate it.
Combustion AnalysisSlide8
Combustion Analysis
Determines what elements are present and in what quantities.What is a combustion reaction?
Unknown + O
2
H2
O and CO2How might this method work?Discuss with your group.Slide9
Combustion Analysis
Law of Conservation of Mass (Return of the Lego Atoms)
Matter cannot be created or destroyed
Whatever atoms are present in the reactants must also be present in the products but may be combined in different forms.
Tells us the % composition of the compound.Slide10
% Composition
What is % composition of a compound?The percent of each element found in the compound.
By massSlide11
% Composition: Penicillin
53.9 % Carbon4.8 % Hydrogen7.9 % Nitrogen
9.0 % Sulfur
6.5 % Sodium
17.9 % OxygenSlide12
Determining Empirical Formula
Step 1: % to mass
Convert mass percentages to mass.
Assume total = 100 g (easy math!)
What are the masses for each element from the percent of each?Slide13
Step 2: Mass
Moles
How can we convert the mass of each element present to moles of each element present?
We have grams of each element…
Convert grams moles
How?Divide the amount of grams by the amount of grams/mole.Slide14
How many moles of each do you have?
C = 4.49 mol
C
H = 4.8
mol HN = 0.56 mol NS = 0.28 mol
SNa = 0.28 mol NaO = 1.12 mol OSlide15
Step 3: Divide by Small
Divide the number of moles of each by the chemical with the smallest number of moles.
C = 4.49
mol
CH = 4.8 mol HN = 0.56 mol NS = 0.28
mol SNa = 0.28 mol NaO = 1.12 mol OWhich is the smallest number of moles?0.28 molDivide all the mole values by 0.28Slide16
Step 3: Divide by Small
C = 4.49 / 0.28 =
16
H =
4.8 / 0.28 =17N = 0.56 /0.28 =2S = 0.28
/ 0.28 =1Na = 0.28 /0.28 =1 O = 1.12 /0.28 = 4Slide17
The whole numbers are the subscripts (number of moles of each in compound)
C = 16
H = 17
N = 2
Na = 1O = 4S = 1C16H
17N2NaO4S = the empirical (lowest whole number ratio) formula for penicillin!Slide18
Empirical Formula of a Hydrate Lab
Jan 6, 2014ChemistrySlide19
Title: Empirical Formula of a Hydrate
The following should be in your lab NB:Purpose
:
Find the empirical formula of copper(II) sulfate hydrate by decomposition to its anhydrous form.Materials:
hydrate, burner, balance, small test tube, ring stand, test tube holder, scoop, test tube clampyou might want to leave out the part about test tube and test tube clamp until you get to the lab.Slide20
Anhydrate
Hydrate
Definition:
A
hydrate which has had the water removed from it.
(
dehyrate
)
A compound that has a specific number of water molecules bound to each formula unit
Applications:
Desiccants
hydration
Uses
in everyday life:
(these are examples or places these compounds are found in)
Shipping/packaging
Sodium oxide
(lye with water
removed) critical component of making glass.
Double pane windows (so condensation doesn’t form between panes)
Gypsum
Plaster of Paris
Epsom
salt
Borax – cleaning agent (laundry)
Desalination –removing salt from water
lotions, shampoos, lip balmsSlide21
Types of Hydrates
Efflorescent Hydrates: Spontaneously lose water
Hygroscopic Hydrates:
Spontaneously gain water
Don’t become completely dissolved to form solutionsDeliquescent Compounds:absorb water from atmosphere until dissolved as a solutionSlide22
Hygroscopic Compound Use
Silica gel packetsOften packaged with electronics and leather goods.
Hygroscopic hydrate – removes moisture from the airSlide23
Equation
We’re using Copper(II) sulfateWhat’s the formula for Copper(II) sulfate?
CuSO
4
And we’re going to add water…How many waters are attached?We don’t know so we put nH2
OFor numbers of waters, you use the prefixes we learned in naming molecular compounds.The notation for hydrates uses a dot:CuSO4 nH20 We’re going to dehydrate it in lab, now suggest an equation:
CuSO
4
nH
2
0
CuSO
4
+ nH
2
OSlide24
Procedure
In the lab, there is a container of Copper(II) sulfateTake just one scoop with the
scoopula
and place it into either the test tube or evaporating dish at your lab station.
You will heat it (we’ll talk about heating) to drive off all the water From both the Copper(II) sulfate AND the vessel it’s in.Slide25
How do you determine n?
What could you measure?mass
What is empirical formula?
Mole ratio
It’s a mass to moles conversionYou should get an integer (that’s why we used n)…the better your lab technique, the better the results.You have to figure out what mass to take in the lab.Slide26
Lab Safety
Personal Protective Equipment (PPE) Required:
Goggles
Lab Apron
If any Copper(II) sulfate gets on your skin, tell me and wash it off. You’ll surviveWhen working with open flames/heat sources, assume EVERYTHING is hot!Don’t touch with your hands/fingers.
Never leave your burner unattended!Keep anything flammable well away from the source of the fire.Tie back long hairRoll up sleevesWatch out for drapey/flowy sleevesSlide27
Lab Techniques
Test Tube
Inspect for cracks BEFORE heating
Only use proper test tube clamps
Point opening of test tube AWAY from anyone’s faceHeat gently and uniformly
Don’t hold it in just one spot over the flame.As condensation appears, you will move it up the tube until it is all removed.Evaporating dish
Only use proper evaporating dish tongs
Don’t put your face over the dish (you don’t want to breathe in any fumes)
Remember
from your lab safety training that we treat all chemicals in the lab as hazardous!Slide28
How to use the butane torch:
Safety offNo golden fire – incomplete combustion
Two parts to the flame
Blue cone
Inner blue coneHottest part of the flameDon’t mass super hot things, give them a minute to cool.
Place the test tube in the beaker to mass it.Evaporation dish can be placed directly on analytical balance.Use the tare (zero) button before you massYou now have 5 min to work with your partner and come up with an outline of a procedure you will follow.Be sure to know why you’re doing what you’re doing and what you’re going to do before entering the lab.