Analysis of a Mixture



Name: ______________________ Lab Partner: __________________ Date: _______

JHS Discrete Chemistry

Separation of a Sand/Salt Mixture Lab

Introduction:

Most of the substances that we come in contact with every day – from the air we breathe to the water we drink and the foods we eat – are mixtures. Chemists frequently work with mixtures. Usually, only one component of the mixture is desired, while the other components are considered to be impurities. Chemists have developed techniques to remove the desired component from the impurities or to isolate each individual substance in the mixture. A great amount of a chemist’s time goes into separating mixtures using techniques such as filtration, distillation, and chromatography.

In this experiment, a heterogeneous mixture of sand/salt will be separated into its component parts. Differences in solubility allow the salt to be dissolved in water; leaving the sand still in its solid phase. The salt water is separated from the sand through filtration; the sand remains in the filter paper and the salt (now in the salt water) is collected. The salt is recovered by evaporating the water from the salt-water solution. The sand is then dried. Hence, the components of the sand/salt mixture are separated.

Mass percent composition is a convenient way to express the actual composition of a mixture in terms of the amount of each component. The mass percentage of each component in a mixture is calculated as follows:

In order to determine the percent composition of a mixture, it is necessary to separate the components without loss of any sample, and then measure the mass of each recovered component. The sum of the mass percentage of all components in a mixture equals 100%.

Objective:

The purpose of this experiment is to study the physical properties of salt, sand, and water and use the information to carry out a procedure to separate these substances. The mass percent composition of the mixture can be calculated from the masses of the recovered components.

|Caution: |

|Handle glassware gently. Sign: ___________________ |

|Goggles required. Date: ___________________ |

Pre-Lab Questions:

1. A flow chart is often used to illustrate the steps involved in the separation of a mixture. In a flow chart, the substances in the mixture are listed inside boxes and are connected by arrows. Imagine a sample of seawater was collected at the beach. There is a liquid layer, consisting of dissolved salt in water, and solid sand particles suspended in the liquid. How can these components be separated? The flow chart in Figure 1 shows one possible method for the separation and recovery of the components in our hypothetical seawater sample.

Think about the separation process outlined in Figure 1 and complete the flow chart to reveal the identities of the solid, liquid, and, vapor components.

2. The Department of Transportation uses a mixture of sand and salt to de-ice roadways in the winter. The mixture contains 8.35 tons of salt and 6.28 tons of sand. What is the mass percent of each component in the mixture? (Include mathematical set-up, and answer)

|% Composition Salt |% Composition Sand |

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3. A bakery needs a mixture of flour and sugar to make cookies. The mixture should contain 62.5 % flour and 37.5% sugar. You are in charge of ordering the components to make

125 kg of the mixture. How many kilograms of flour and sugar should be ordered?

Procedure:

1. Using a 150 mL beaker, obtain a scoop of a sand salt mixture from your teacher. Record the mass of the mixture in your data table. Refer to the Data Table

2. Measure about 20 ml of water and pour it into the beaker. Stir the mixture (about one minute) using a stirring rod thoroughly until you are confident all the salt has dissolved.

3. Initial (using a pencil) and weigh a piece of filter paper. Record the mass on the data chart. Fold the paper into a cone and place it into a funnel.

4. Assemble the following set-up:

✓ Ring stand with a ring clamp attached.

✓ Clay triangle placed on ring clamp

✓ Place the funnel (with folded filter paper) in the triangle.

✓ Carefully weigh a dry 250 mL beaker, record the mass on the

data chart. Place this clean and dry 250 mL beaker beneath

the funnel. To avoid splattering, make sure the end of the

funnel is inserted into the 250 mL beaker.

5. Swirl the mixture of sand, salt and water and immediately pour the mixture into the

funnel, getting as much sand onto the filter paper as possible. Rinse the remaining

sand out of the beaker using a wash bottle.

Warning: Don’t use a lot of water. This will increase the time needed to evaporate the water.

6. Remove the marked filter paper containing the sand from the funnel hand it over to

your teacher. Once the filter paper containing sand is dry carefully weigh it.

Record the mass of the sand on the data table.

7. Place the beaker containing the salt solution on a hot plate. BE CAREFUL NOT

TO LET THE SOLUTION SPLATTER. Weigh the beaker and its contents and

record the mass of the salt on the data chart.

Data:

Show all measurements in significant figures and proper units.

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| |Mass of 150 mL beaker = _________ |

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|Mass of sand salt mixture obtained | |

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| |Mass of 150 mL beaker + sand/salt mixture = _________ |

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| |Mass of sand/salt mixture = _____________ (Hint: Subtract!) |

|Mass of 250ml beaker used under funnel | |

|Mass of initialed filter paper before placed in funnel | |

|Mass of filter paper and dried sand | |

|Mass of dry sand | |

|Mass of 250ml beaker and dried salt | |

|Mass of dry salt | |

Calculations:

1. Find the percent sand and the percent salt in the original mixture using the following units. Show all work using significant figures and show all units.

Percent by mass of sand in the mixture

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|Answer:________ |

Accepted Value % sand (obtained from teacher) = ____________

Percent by mass of salt in the mixture

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|Answer:_________ |

Accepted Value % salt (obtained from teacher) = ____________

Questions:

1. Calculate your percent error (Table T) for your sand and salt values. Show the work of both calculations.

|% Error for sand |% Error for salt |

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2. Suggest two possible sources of error. Do not include errors in mass measuring.

Possible error #1

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Possible error #2

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3. Why should splattering be avoided while evaporating the salt solution?

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4. A student weighs out a 12.6-gram sample of a sand salt mixture. The student separates the mixture and has an experimental yield of 3.3 grams of salt. What is the percent salt in the mixture according to the student’s values?

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5. Another way of separating a mixture is through distillation. Look up this technique and describe how you would separate a mixture containing the following: water, gasoline, and alcohol.

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6. Base your answers to questions a through c on the particle diagrams below, which show atoms and/or molecules in three different samples of matter at the same temperature and pressure.

[pic]

a. Which sample represents a pure substance? ___________________

b. When two atoms of y react with one atom of z, a compound forms. Using the

number of atoms shown in sample 2, what is the maximum number of molecules of

this compound that can be formed? __________________

c. Explain why does not represent a compound.

___________________________________________________

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6. Given the diagram representing a process being used to separate the colored dyes in food coloring:

[pic]

__________ Which process is represented by this diagram?

(1) chromatography (2) electrolysis (3) distillation (4) titration

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