LAB 1. SEPARATION OF MIXTURES:
BASIC LABORATORY TECHNIQUES
PURPOSE: To become familiar with the function and use of common laboratory equipment.
To learn techniques of measuring mass and volume
To separate a mixture of salt and sand into its components.
To calculate the % composition of an unknown mixture.
SAFETY CONCERNS:
Always wear safety goggles.
LABORATORY TECHNIQUES:
Measuring Volume:
Graduated Cylinders are tools for accurately measuring the volume of liquids. They have more
accurate markings than a beaker or Erlenmeyer flask, but have less accurate markings than a pipette,
buret, or syringe. All types of volumetric glassware have a slender, cylindrical shape in the
measuring region which causes the surface of most liquids to be curved downward. Take readings
from the bottom of the curved surface (called the meniscus) with your eye at the same level.
A: Read the bottom of a concave meniscus.
B: Read the top of a convex meniscus.
If the volumetric glassware that you are using has a number of graduations, estimate the volume as
accurately as you can by noting the position of the meniscus between the graduations. See Figure 2-5.
90
80
Figure 2-5 The proper method of reading the meniscus. The reading is 85.5 mL.
The scale divisions on a graduated cylinder are generally determined by its size. For example, the 50mL graduated cylinder is divided into 1 mL increments. However, the scale of a 10-mL graduated
cylinder is divided into 0.1 mL increments, and the scale of a 500-mL graduated cylinder is divided
into 5 mL increments. The graduated cylinder scale is a ruled scale, and it is read like a ruler.
CH110 Lab 1. Separation of Mixtures
1
Measuring Mass:
When performing chemical reactions in the laboratory we often need to measure the mass of our
ingredients. The techniques for measuring mass using an electronic balance will be explained
and practiced in the experimental section of this lab. Our balances measure mass in grams.
Filtration:
Filtration is the common process used to separate an insoluble solid from a liquid. Layers of
rock and sand and algae are used to filter impurities from water to make it drinkable. Breweries
use fine millipore filters to filter out harmful bacteria.
In the laboratory the filtration process is carried out using a funnel and filter paper. The liquid
that passes through the filter paper is called the filtrate, and the solid that remains on the filter
paper is the precipitate or residue.
Evaporation:
Most substances that dissolve in a liquid (solutes) can be recovered from solution by evaporating
the liquid portion (the solvent) over a direct flame, a hot plate, or a steam bath.
The size of solid crystals often relates to the rate of evaporation of the solvent. Slowly
formed crystals are usually larger than crystals formed rapidly.
2
CH110 Lab 1. Separation of Mixtures
N
OTES:
1
PROCEDURES:
ACTIONS:
I. MEASUREMENTS:
MASS
1. Obtain a weighing boat or shiny weighing paper1 and
place it on the pan of an electronic balance. Press
Chemical powders and liquids should never be
placed directly on the metal balance pan since
they may cause corrosion. Shiny paper or boats
are used so that powdered materials will slide off
easily. If porous paper, like filter paper or paper
towels, were used instead of shiny materials, then
powders might get caught in the fibers and be lost.
If you are using weighing paper then fold it into
quarters by folding in half, opening, and then
folding in half again the other direction. Open up
the paper and place it on the balance pan.
the “Tare” or “Zero” button on the face of your
balance to set the mass of the paper to zero.2
2. With your lab scoop or metal spatula, put enough
salt/sand mixture on the weighing paper to measure
about3 2 grams. Record the exact mass on your
report sheet (Box IA) to 3 places behind the decimal
according to the accuracy of your balance.
3. Carefully remove the weighing paper with the salt/sand
mixture from the balance and transfer it to a 125 mL or
250 mL Erlenmeyer flask. 4
VOLUME:
4. Measure 7 mLs of water using a graduated cylinder5.
The bottom of the meniscus6 should be right at the 7
mL line of the graduated cylinder.
2
The tare button will set the recorded weight of
your paper to 0.000 grams. Now when you add
solid to the paper the balance will show only the
added mass of the solid. If you do not tare the
balance after the weighing paper is applied, then
you would have to subtract the mass of the paper
from your total mass to get the mass of your
substance alone.
3
The mass does not have to be exactly 5.000
grams but could be anywhere between 4.800 and
5.200 (5.000 + 0.2); (for example 5.025 or 4.987
etc.)
4
The shape of an Erlenmeyer flask makes
swirling/mixing materials less likely to splash or
spill than if done in a beaker.
5
5. In Box IB of your report sheet draw a picture of the
meniscus in your graduated cylinder. Include a couple
of graduation markings on your cylinder drawing
above and below.
II. SEPARATION OF SALT AND SAND:
6. Add the 7 mLs of deionized water from the graduated
cylinder to the Erlenmeyer flask of salt/sand mixture.
Swirl to completely dissolve the salt to make a salt
water solution. 7
7. Mass two porcelain evaporating dishes. One for sand
and one for salt. Record these values.(Box IIC & D) 8
8. Set up a ring stand with an iron ring and a funnel
suspended over the massed porcelain evaporating dish
for salt.
9. Flute9 a piece of filter paper and insert it into the
funnel.
For fine control of your water level you can use
an eye dropper for the last bit of water. Always
hold eye droppers upright with the glass tip
pointing down. Natural vacuum will keep the
liquid from spilling. Do not tip the dropper back
or the vacuum will be broken and the filling will
run into the bulb and get contaminated, or air may
enter the dropper and cause the contents to spill.
6
Water forms a meniscus in any glass tube or
cylinder because water is attracted to glass and
will try to climb the sides of a glass container.
We measure the amount of water in a glass tube
from the bottom of the meniscus.
7
If the salt is not completely dissolved then it will
remain solid and be filtered out of solution with
the sand. Thus your results will show less salt and
more sand than actually present.
8
Keep the dishes separate so you know which dish
goes with which mass.
9
To flute filter paper:
1) fold in half
2) fold again into quarters
3) fold back and forth from the point as if making a
fan
4) unfold the paper into a cone that will fit into a
funnel.
10. Perform a filtration by periodically swirling the
Erlenmeyer flask solution of salt with sand to keep it
mixed, and pouring the solution down a stirring rod10
into the filter paper.
11. Rinse any residual materials from the Erlenmeyer flask
into the filter using a squirt bottle of deionized water.
1)
3)
4)

2)
10
The stirring rod helps to channel the flow of
liquid to prevent dripping.
CH110 Lab 1. Separation of Mixtures
3
12. Remove the filter paper containing the sand
residue and transfer the sand with a lab scoop or
spatula to the massed porcelain dish for sand.
13. Place the porcelain evaporating dishes containing
the filtrate salt solution and the residue sand on a
hot plate and slowly13 heat to evaporate the water
from them.
14. When dry mass the paper and sand and subtract
the mass of the paper () to determine the final
mass of sand collected.11
15. Mass each of the evaporating dishes with the now
dry salt (Box IIA) and sand (Box IIB) and subtract
the mass of the respective dishes (IIC & IID) to
determine the final masses of salt (IIE) and sand
(IIF) collected.
16. Determine the percent12 of salt (IIG) and percent
of sand (IIH) in your original mixture.
11
You’ll subtract the mass of the filter paper from the
mass of the paper/sand combination in order to
determine the mass of the sand collected. You’ll
subtract the mass of the evaporating dish from the mass
of the dish/salt combination to determine the mass of
salt.
12
Percent composition is the “part” divided by the
“whole” X 100 or:
“part” X 100 = %
“whole”
In this case the “whole” is the mass of the original salt
and sand mixture.
The “part” is the mass of the sand or the mass of the
salt.
13
Heat slowly so the solution doesn’t splatter. Stirring
with a glass stirring rod may also help prevent
spattering.
14
Do your percent compositions of salt and sand total
100? Why or why not? What might some of the errors
be in your procedures or techniques?
17. Describe the salt crystals formed.
18. Assess the quality of your results and make some
conclusions about your data. 14
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CH110 Lab 1. Separation of Mixtures
LAB 1. SEPARATION OF MIXTURES:
REPORT:
NAME___________________
PARTNER_________DATE___
I. MEASUREMENTS:
A. Mass
B. Volume
Salt/Sand Mixture _________________g
(Add labels & meniscus) __
___
___
(report to the accuracy of the balance)
____
__
____
II. SEPARATION OF SALT AND SAND
A.
Mass of Evaporation dish with Salt ___________g
B.
Mass of Evaporating dish with Sand ___________g
(report to the accuracy of the balance)
(report to the accuracy of the balance)
D.
Mass of Empty Evaporation dish for Sand
Mass of Empty Evaporation dish for Salt
______________g
_________________g
C.
(report to the accuracy of the balance)
(report to the accuracy of the balance)
E.
Mass of Salt alone
________________g
F.
Mass of Sand alone
(report to the accuracy of the balance)
____________g
(report to the accuracy of the balance)
G.
% Composition of Salt in the mixture:
H.
% Composition of Sand in the mixture:
(show the calculations)
(show the calculations)
Describe the salt crystals formed:
ANALYSIS & CONCLUSIONS:
CH110 Lab 1. Separation of Mixtures
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LAB 1. SEPARATION OF MIXTURES:
LAB EXERCISES:
NAME_____________
DATE______________
1.__
The curve of the surface of a liquid when placed in a cylindrical tube is called the
A residue.
B. filtrate.
C. meniscus.
D. tare
2.__
To set the mass of an object to zero on an electronic balance is called to
A residue.
B. filtrate.
C. meniscus.
D. tare
3.__
The material that passes through a filter is called the
A residue.
B. filtrate.
C. meniscus.
D. tare
4.__
The material that remains in the filter paper after a filtration is called the
A residue.
B. filtrate.
C. meniscus.
D. tare
5.
A student, Earl N. Meyer, is given a 5.000 g sample of a mixture of salt and sand. Earl
added water to the mixture, filtered out the sand, evaporated off the water from the salt
and weighed his final products. He ended up with 1.500 grams of salt and 3.900 grams of
sand.
A. What was the % concentration of salt in Earl’s mixture? Show your calculations
B. What was the % concentration of sand in Earl’s mixture? Show your calculations
C. Assuming there were no mistakes in the reading of the balance, give some
explanations for why the percent compositions of Earl’s salt and sand don’t total
100%.
6.
6
If the water was allowed to evaporate from your salt water solution at a slow rate rather
than quickly over a hot plate how might the crystals appear different?
CH110 Lab 1. Separation of Mixtures