Experiment-4: Separation of a Salt and Sand mixture

Solubility
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Decantation

Evaporation
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% Calculations
Matter is anything that has certain mass and occupies space. Chemistry is scientific
study of composition, characteristics, transformations, and interactions of matter. Three
stable physical sates of matter are: solids, liquid, and gas. Solids have a definite shape
and define volume. Liquids have an indefinite shape but a definite volume. Gases have no
definite shape or volume. A set of physical and chemical properties is used to identify,
describe, and characterize a chemical. Physical properties can be observed without
changing the chemical composition of the substance. Color, odor, size, boiling point,
melting point, density, solubility, and taste are examples of physical properties. A
chemical property is a unique characteristic of a chemical that describes the way the
chemical interacts with other chemicals to form new chemical(s). The properties of a
chemical can be classified in a second manner- as intensive or extensive properties.
Intensive properties are independent of the amount of substance, for example
temperature, density, color, melting point and boiling point. Whereas, extensive
properties do depend on the amount of substance (sample size); for example mass, length,
and volume. Solubility is defined as maximum amount of solute that will dissolve in a
given amount of solvent at a given temperature. It is expressed as grams of solute per
100 g of solvent. An aqueous solution is a solution in which water is solvent. Solubility
is a temperature dependent parameter. Solubility of solids and liquids increases with
increasing temperatures in most cases. A mixture is a physical combination of two or
more pure chemicals in which each chemical retains its own chemical identity. In this
experiment, you are given a mixture, which has two components: salt (NaCl) and sand
(SiO2). NaCl is water-soluble but SiO2 is not. You will separate the components based on
this selective solubility feature, and then find their respective weights to calculate the %
composition.
% of salt = (grams of salt recovered / grams of mixture) x 100
% of sand = (grams of sand recovered / grams of mixture) x 100
Theoretically, % of salt plus % of sand should be equal to 100 %.
Procedure:
1. Record your unknown sample number__________.
2. Find the mass of a clean 100 or 150-mL beaker. Record all the digits throughout
the experiment. Label this as beaker#1.
3. Carefully transfer approximately 2 grams of your unknown sample into beaker#1.
Find the mass on beaker#1 plus the unknown sample.
4. Transfer 20 mL water to beaker#1. Stir the mixture using a glass rod. Let it stand
for a minute or two so that the sand settles.
5. Find the mass of a clean 250-mL beaker. Label this as beaker#2.
6. Carefully decant the top liquid from beaker#1 into beaker#2.
7. Transfer 10 mL water to beaker#1. Stir the mixture using a glass rod. Let it stand
for a minute or two so that the sand settles.
8. Carefully decant the top liquid from beaker#1 into beaker#2.
9. Transfer 10 mL water to beaker#1. Stir the mixture using a glass rod. Let it stand
for a minute or two so that the sand settles.
10. Carefully decant the top liquid from beaker#1 into beaker#2.
11. At this stage, beaker#1 is left with wet sand and beaker#2 contains 40 mL
(20+10+10) of aqueous salt solution.
12. Using a hot plate, heat beaker#1, gently at first, and then more vigorously to get
rid of all the water from the sand. When it is completely dry you will see granular
sand powder. Remove the beaker from the hot plate and let it cool. Now, find the
mass of beaker#1 and dry sand recovered.
13. Using a hot plate, heat beaker#2, gently at first, and then more vigorously to
evaporate all the water from the salt solution. Beaker#2 should be covered with a
watch glass to avoid spattering especially when you see white salt crystals
appearing. When it is completely dry you will see granular salt powder. Remove
the beaker from the hot plate and let it cool. Now, find the mass of beaker#2 and
dry salt recovered.
14. Calculate % of salt and % of sand.
15. Discard sand into regular waste bin. Do not throw sand into the sink.
16. Discard salt into regular sink.
Laboratory Report#4:
Separation of a Salt and Sand mixture based on selective solubility
Last Name_____________________________, first name________________
Date of Experiment______________ Instructor’s Initials__________
Data and Calculations
1. Your Unknown sample #_____________
2. Mass of empty and dry beaker#1
=_____________________g
3. Mass of beaker#1 with Unknown sample
=_____________________g
4. Mass unknown sample used
=_____________________g
= #3-#2
5. Mass of empty and dry beaker#2
=_____________________g
After separation, drying, and cooling
6. Mass of beaker#1 containing dry sand
=_____________________g
7. Mass sand recovered
=_____________________g
= #6-#2
8. % Sand = (#7/#4) x100
=_____________%
9. Mass of beaker#2 containing dry salt
=_____________________g
10. Mass of salt recovered
=_____________________g
= #9-#5
11. % Salt = (#10/#4) x100
12. % of the unknown sample recovered
=_____________%
= #8+#11
=_____________%
Show all your work! Use proper units and significant figures !!
1. A salt and sand mixture weighs 44.867 g. This sample contains 12.547 g of salt.
Calculate % of salt and % of sand.
2. How would you separate a mixture of iron nails, salt and sand?
3. Explain if #12 is different from 100%. List possible sources of error.
4. Explain the effect of temperature on the solubility of CO2 in water.