Transcript Percentage Composition

Percentage Composition
SCH3U
S
In a group, calculate the percentage
of flasks, owls, Marios, pencils &
stars
6g
100 g
20 g
2g
50 g
What if this was related to mass? Calculate the % by mass
for each of the objects.
Oreos
S Obtain an Oreo. The cookie is made up of WAFER and CREAMY
FILLING. Using a balance, a plastic knife and a napkin (to keep
the cookie from directly touching the balance), calculate the percent
of the cookie that is made up of each part. You have 10 minutes to
complete and be ready to explain the process and your answer.
% of Creamy Filling
Regular Oreo Cookie
1
2
3
4
5
6
Double Stuffed Oreo
Fruit
S Obtain a small slice of fruit. Find the percent of water in the piece
of fruit.
S What do you have to do first?
S Mass out your sample using a balance
S You will have to leave the sample in the drying oven overnight at
200°F.
Percentage Composition in
YOUR life
Per cent age composit ion of nat ur al
subst ances (like vanilla) can be
det er mined and used t o ident if y t he
chemical f or mula of a compound.
Once chemist s know t he chemical
f or mula, t hey can of t en pr oduce t he
Scompound
Centium
Lab…Metal Composition
in a lab (ar t if icial vanilla).
in Coins
Scientists use the percentage composition of natural
substances to identify the chemical formula of a
compounds. Once the chemists know the chemical formula,
they can often produce the compound in a lab…enjoy your
artificial vanilla!
Law of Definite Proportions
S Elements in a chemical compounds are always
present in the same proportions by mass
S Eg. For water: 2 H for every 1 O
Percentage Composition
S The relative mass of each element in a compound is called
Percentage Composition.
S Mass Percent is the mass of an element in a compound
S Expressed as a percentage of the total mass of the compound
S Eg. Vanillin, C8H8O3, has:
S Mass percent of C = 63.1%
S Mass percent of H = 5.3%
S Mass percent of O = 31.6%
Total:
100%
a percentage composition of 63.1% C, 5.3% H and 31.6% O.
Methods for Calculating
Percentage Composition
S There are two ways to calculate the mass % of each element in a
compound:
Use when
you know
mass
1. Using the mass of the compound and each element
mass % =
mass of the element x 100%
mass of the compound
2. Using the chemical formula of the compound:
mass % =
(# of the element in cpd) x MMelement x
100%
MMcompound
Example 1
S A sample of a compound is analyzed and found to contain carbon,
hydrogen and oxygen. What is the percent composition of the
compound?
msample = 650 mg; mC = 257 mg; mH = 50.4 mg
mO = msample – mC - mH = 343 mg
Mass % C = 257 mg/650mg x 100%
Mass % H = 50.4 mg/650 mg x 100%
Mass % O = 343 mg/650mg x 100%
Therefore the percentage composition of the compound is 39.5% C, 7.75%
H, 52.7% O.
Example 2
S Sulfuric acid is an important acid in labs and industries.
Determine the percentage composition of sulfuric acid.
MMH2SO4 = 98.09 g/mol
Mass % H = 2 x 1.01 g mol-1 /98.09 g mol-1 x 100%
Mass % S = 1 x 32.06 g mol-1 /98.09 g mol-1 x 100%
Mass % O = 4 x 16.00 g mol-1 /98.09 g mol-1 x 100%
Therefore the percentage composition of sulfuric acid is 32.69% S,
2.06% H, 65.24% O.
Fruit Cont…
% of water in fruit
Banana
1
2
3
4
5
6
Grapes
Apple
Oranges
Try These…
S Activity p260 textbook – Mass Percent of Oxygen
S p267 #4, 6, 10, 12, 13
Hydrate Lab
Hydrate Lab
Purpose
The objective of this experiment is to determine the number of moles of w
associated with one mole of copper sulfate, in the hydrate CuSO 4·xH2O(s
The objective of this experiment is to determine the number of
Theory
moles
ofsolids
water
associated
withsolutions,
one mole
of a hydrate.
When certain
ionic
crystallize
from aqueous
they combine
with a definite amoun
water, which becomes a part of the crystalline solid. Salts that contain water as part of their crys
are1.5
called
(or hydrated
salts) and
the water
in the
crystal
Sstructure
Obtain
to hydrates
2.5 grams
of hydrate.
Record
your
data
in structure
a table is called th
of hydration. When the water of hydration is removed from the hydrate, the salt that remains is s
SbeFind
the percent of water present in the sample. You may use any
anhydrous.
presentyouonwillthe
lab counters.
In items
this experiment
remove
the water of hy dration from a known mass of hydrated coppe
heat
by heating the compound in a crucible:
CuSO 4·xH2O(s)
CuSO 4(s) + xH2O(
hydrated salt
anhydrous salt
water
Calculations and questions
By knowing the mass of the anhydrous salt and the mass of water driven off through heating, the
Sof Calculate
the number of moles of water lost (nwater).
the hydrate can be determined.
S Calculate the number of moles of anhydrous salt (nanhydrous salt)
SApparatus
Calculate the number of moles of water lost for every mole of
• Crucible
• Ring clamp
• Bunsen burner
• Balance (wit
anhydrous
salt
(mol
water
÷
mol
anhydrous
salt).
thermal pad)
• Retort stand
• Clay triangle
• Crucible tongs
S The above calculation gives the value of x in your hydrate
Procedure
[CuSO4·xH2O(s)]. Write the correct formula for the hydrate.
Protective eyewear must be worn during this lab. As m uch as possible, handle your crucible wi