WU Chemistry Worksheet

Homework Chapter 11. A 95.0 wt% solution of ethanol (CH3CH2OH, 46.07 g/mol) in water has a density 0.804 g/mL.
a. How many of grams of ethanol are contained in 1.00L of solution?
b. What is the molarity of ethanol in this solution?
c. Find the molality of ethanol in this solution, considering H2O to be the solvent (even
though H2O is really the solute in this case).
2. Describe how to prepare exactly 100 mL of 1.00 M HCl from 12.1 M HCl reagent. Be sure to
include the types of lab equipment and/or glassware and procedure you would use.
3. Sulfuric acid solution reacts with aqueous barium nitrate to form a precipitate.
a. Write a balanced chemical equation for this reaction.
b. 4.35 g of barium nitrate was dissolved in 250 mL of water; then, 12.5 mL of 3.00 M
sulfuric acid solution were added to it. How many grams of precipitate will form?
Chapter 1: Chemical Measurements
Concepts you are familiar with from Chem:
• SI units
• Chemical concentrations
• Solutions, Dilutions
• Gravimetric Analysis
SI Units
Quantity
Unit
Length
Mass
Time
Temperature
Amount of Substance
Meter (m)
Kilogram (kg)
Second (s)
Kelvin (K)
Mole (mol)
Prefixes as Multipliers
You should already be familiar with …
Prefix
Factor
micro (µ)
milli (m)
kilo (k)
10-6
10-3
103
Table 1-3 Prefixes
Prefix
Symbol
Prefix
Symbol
Y
Factor
1024
deci
d
Factor
10–1
yotta
zetta
Z
1021
centi
c
10–2
exa
E
1018
milli
m
10–3
peta
P
1015
micro
μ
10–6
tera
T
1012
nano
n
10–9
giga
G
109
pico
p
10–12
mega
M
106
femto
f
10–15
kilo
k
103
atto
a
10–18
hecto
h
102
zepto
z
10–21
deca
da
101
yocto
y
10–24
Chemical Concentrations
Everything you learned in General Chemistry gets more fun ….
SOLUTION: Homogenous mixture of 2 or more substances
SOLUTE: Minor species in a solution
SOLVENT: Major species in a solution
If the solvent is water = Aqueous solution
CONCENTRATION: How much solute is in a given volume
or mass of solution or solvent
Chemical Concentrations
We can express concentration in 2 ways:
Molarity (M): # moles of substance
L of solution
Molality (m):
# moles of substance
kg of solvent
Which one changes with temperature?
(volume of solution increases with T)
Chemical Concentrations
We can express percent composition in 2 ways:
Weight Percent (wt%):
mass of solute
mass of total sol’n or mixture
Volume Percent (vol%):
volume of solute
x 100
volume of total solution
x 100
Chemical Concentrations
Example 1: Calculate the molarity and molality of 49.0 wt% HF
(hint: density HF solution = 1.16 g/mL)
Chemical Concentrations
Example 1: Calculate the molarity and molality of 49.0 wt% HF
(hint: density HF solution = 1.16 g/mL)
Chemical Concentrations
Sometimes, we have a VERY small concentration …
Keeling Curve – concentration of CO2 in the atmosphere
Chemical Concentrations
Sometimes, we have a VERY small concentration …
Parts per Million (ppm):
g of substance
million g of total sol’n or mix.
Parts per Billion (ppb):
g of substance
billion g of total sol’n or mix.
In aqueous solutions, where density ~1.00g/mL, we can estimate:
1 ppm = 1 µg / mL
1 ppb = 1 ng / mL
Chemical Concentrations
Example 2:
There are ~1.6ppm flouride in drinking water.
What is the molarity of F- in 1L of drinking water?
Preparing Solutions
Example Problem: How many grams of CuCl2∙5H2O are needed to make
500 mL of a solution that is 1000 ppm in Cu?
(MM of CuCl2∙5H2O is 224.53 g/mol)
First calculate the grams of Cu required
(500-mL)  (1000 µg/mL) = 5.0  105 µg Cu
5.0  105 µg Cu = (5.0  105 )(10-6)g Cu
5.0  10-1g Cu
Second, convert to grams of CuCl2∙5H2O (using mass and molar ratios)
 224.53 g CuCl 2 5H 2 O / mol
5.0 x 10 g Cu  
63.546 g Cu /mol

(
-1
)

 = 1.76 7 g CuCl 2 5H 2 O

Preparing Solutions
Dilution Equation:
Example Problem: How many milliliters of concentrated HCl are needed
to make 500 mL of a solution that is 0.250 M in HCl?
Preparing Solutions
Example Problem: How many milliliters of concentrated HCl are needed
to make 500 mL of a solution that is 0.250 M in HCl?
(Mconc)(Vconc) = (Mdil)(Vdil)
First, we need to know molarity of concentrated HCl.
Concentrated HCl is 37.2% (w/w) HCl and has a density of 1.188 g/cm3
c = 37.2% = 37.2 gHCl / 100 gsoln
MM = 36.46 g/mol
d = 1.188 g/cm3
}
desired units
mol HCl
L soln
37.2 g HCl x 1 mol HCl x 1.188 g soln x 1000 cm 3soln
= 12.1 mol/L
3
100 g soln
36.46 g HCl 1.000 cmsoln
1L
Preparing Solutions
Example Problem: How many milliliters of concentrated HCl are needed
to make 500 mL of a solution that is 0.250 M in HCl?
(Mconc)(Vconc) = (Mdil)(Vdil)
Mconc. HCl = 12.1 M
(Mconc)(Vconc) = (Mdil)(Vdil)
(12.1M)(Vconc) = (0.250 M)(500 mL)
Vconc = (0.250 M)(500 mL / (12.1 M)
Vconc = 10.3 mL
Gravimetric Analysis
Gravimetric Analysis:
Chemical analysis based on weighing a final product
Precipitations are a common example of
gravimetric analysis
→ Gravimetric Analysis, must have enough
final product to weigh accurately!
Gravimetric Analysis
100.0 mL of sample containing an unknown amount of NaCl is reacted
with an excess of AgNO3. During reaction, 71.7 mg of AgCl precipitates.
What is the [NaCl] in the unknown?
EXPERIMENT 1: INTRODUCTION TO ANALYTICAL TECHNIOUEs
The purpose of this first lab is to familiarize you with basic analytical techniques. You
will use an analytical balance to determine variation in weight among a given set of
samples. Additionally, you will determine the reproducibility of the analytical balance.
You will also practice making diluted solutions, determine the accuracy of your pipet,
and become familiar with titration techniques. Finally, you will compare gravimetric and
volumetric measurements.
Chemicals/Reagents and additional materials required:
• Pennies (5 per student)
•
•
•
Stock sulfuric acid (H2S04) solution (50mL per student)
0.1M sodium hydroxide (NaOH) solution (2L per student)
Phenolphthalein indicator solution (l dropper bottle per student)
I. EXPERIMENTAL
A. Gravimetric Measurements
1. Weigh each coin in your set individually.
2. Select one of your coins to reweigh. Weigh this coin, remove from the pan
and re-zero the balance, then reweigh. Repeat until you have weighed the coin
5 times.
B. Comparison of Gravimetric and Volumetric Accuracy
l. Fill a beaker with deionized water. Tare a large plastic balance pan. Pipet
2.00 mL of deionized water into the pan. Weigh the water. Re-tare the
balance, pipet another 2.00 mL of water into the pan, and reweigh. Repeat the
process until you have 5 weights.
2. Measure the temperature of the water in your beaker.
C. Volumetric Measurements
l. Dilute 10.00 mL of the stock 1–12S04
to 100.00 mL, using a pjpgLand a
volumetric flask.
2. Pipet three 5.00 mL aliquots of your diluted 1-12S04
solution into three 250 mL
Erlenmeyer flasks. Add 2-3 drops of phenolphthalein
indicator to each.
Titrate with 0.1M NaOH to the first permanent pink
color.
8
Chapter 1: Chemical Concentrations
1. Typical seawater contains 0.054 M magnesium chloride (MgCl 2)
a. How many grams of MgCl2 are present in 25mL of seawater?
b. If the density of seawater is 1.028 g/mL, what is the weight percent (wt%) of MgCl2?
2. You have exactly 505mL of 0.125 M HCl solution and you want to dilute it to exactly
0.100M. How much water should you add?
1
3. An aqueous solution that contains 137g of NaCl has a volume of 11.0 L and a density of
1.01 g/mL. Calculate the concentration of NaCl in molarity, molality, and ppm.
2