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General Chemistry I CHEM- Laboratory Experiment No. 2 Physical Separation Techniques
Introduction
When two or more substances that do not react chemically are blended together, the components of the mixture retain their individual identity and properties. The separation of the components of a mixture is a problem frequently encountered in chemistry. The basis of separation theory is the fact that components of a mixture have different physical and chemical properties. The components are pure substances, either elements or compounds. Under the same conditions of pressure and temperature, the properties of every sample of a pure substance are identical. Each sample melts at the same temperature, boils at the same temperature, has the same solubility in a given solvent, etc.
Although these and other characteristics can be used to identify a particular substance, we will be concerned in this experiment with the separation of a mixture into its components, not with the identification of the substances. Techniques used to separate mixtures rely on differences in the physical properties of the components. Techniques used for separation of mixtures include:
Distillation: The purification of a liquid by heating it to its boiling point, causing vaporization, and then condensing the vapor and collecting the liquid. Nonvolatile solids are easy to remove from a solution because they do not vaporize and are left behind during distillation. Separation of a mixture of two liquids requires that they have different boiling temperatures. Decreasing the pressure over the liquid will reduce all boiling temperatures.
Extraction: The removal of one substance from a mixture by use of a solvent that will dissolve one component but not the other.
Filtration : The process of removing or “straining” a solid (sometimes called a precipitate) from a liquid by the use of filter paper or other porous material.
Decanting : Pouring a liquid from a solid-liquid mixture, leaving the solid behind.
Sublimation: The physical process by which some substances can pass directly from the solid state to the gaseous state without the appearance of the liquid state. Not all substances possess this characteristic. If one component of a mixture sublimes, this property may be used to separate it from the other components of the mixture. Iodine (I 2 ), naphthalene (C 10 H 8 , mothballs), ammonium chloride (NH 4 Cl) and dry ice (solid CO 2 ) are substances that sublime easily.
Centrifuging: The process of separating a suspended solid from a liquid by spinning the mixture at high speed.
Chromatography: The separation of a mixture by the distribution of its components between a stationary phase and a moving phase. Some examples are gas chromatography, paper chromatography, and thin-layer chromatography.
In this experiment you will separate a three-component mixture of sodium chloride, iron filings, and silicon dioxide into its individual components. Measuring the mass of the original mixture and measuring the masses of the pure components will allow you to calculate the percent by mass of each substance in the original mixture.
The scheme used to separate the components of a mixture is based on differences in the physical properties of the three components. Chemists frequently illustrate a separation procedure with a flow chart like the one depicted in the Prestudy. By knowing the physical properties of each component, they decide what physical separation techniques will allow them to separate the mixture. In this experiment’s Prestudy, you will look up the pertinent physical properties of some three components of a mixture and create a flow chart describing the separation procedure.
Safety Chemical splash goggles must be worn at all times during this and all chemistry experiments, from the very beginning to the very end of the time you spend in the laboratory.
Disposal Dispose of the iron in the heavy metal waste container. You may rinse sodium chloride residues down the drain with water. Dispose of the sand you isolate from the mixture in the regular trash can.
Cleanup At the end of the lab period, wipe down all your work surfaces with a damp sponge.
Experimental Procedure
- Obtain an unknown solid mixture and record its number.
- Using a weigh-boat, determine the mass of your unknown solid mixture to the nearest 0.001g
A. Separation of Iron Filings. Place the bar magnet inside a sandwich bag. While holding one end of the magnet, move the other end through the mixture. The iron filings will stick to the magnet. Shake gently to remove any trapped sand. It is not necessary to remove all the iron filings at one time.
Gently lift the magnet with the iron filings and place the end with the filings inside a preweighed 100-mL beaker. Fold the plastic bag over the beaker. Carefully pull the magnet out of the bag, leaving the filings in the beaker.
Repeat twice to remove the last traces of iron filings from the sand-salt mixture.
Determine the mass of the 100-mL beaker with the iron filings to the nearest 0.001 g.
Calculate the mass of NH 4 Cl in the mixture.
General Chemistry I CHEM- Laboratory Experiment No. 2 Physical Separations Techniques Data page
Unknown Number _____________________
- Mass of original sample _______________________
- Mass of 100-mL beaker _______________________
- Mass of 100 - mL beaker + iron filings _______________________
- Mass of iron filings in original sample _______________________
- Mass of 400 - or 600 - mL beaker and watch glass _______________________
- Mass of dry filter paper _______________________
- Mass of filter paper plus dry SiO 2 _______________________
- Mass Of SiO 2 in original sample _______________________
- Mass of 400 - or 600-mL beaker, watch glass, and dry NaCl _______________________
- Mass of NaCl in original sample _______________________
General Chemistry I CHEM- Laboratory Experiment No. 2 Physical Separation Techniques Report and Calculations
For full credit, show all your calculation setups clearly. All answers must contain the correct units and the correct number of significant figures.
- Calculate the percentage of iron filings in the mixture.
- Calculate the percentage of silicon dioxide in the mixture.
- Calculate the percentage of sodium chloride in the mixture.
General Chemistry I CHEM- Laboratory Experiment No. 2 Physical Separations Techniques Prestudy (first of two pages)
- Use the CRC Handbook of Chemistry and Physics or other suitable reference on-line or print references to look up the physical properties of ammonium chloride (NH 4 Cl), silicon dioxide (SiO 2 , sand, quartz), and sodium chloride (NaCl, table salt) and enter them in the table. (4 points)
Substance Formula (^) Melting Point ( C) Solubility* †^ Appearance
sodium chloride NaCl
ammonium chloride NH 4 Cl white powder
silicon dioxide (crystabolite)
SiO 2
*Do not use the triple point (tp) for ammonium chloride; use the sublimation point (sp). †Solubility: soluble (s) or insoluble (i) in water
- A student is given a 3.589 g mixture of iron filings, calcium chloride and sand. She separates the mixture and recovers 0.897 g of iron, 0.923 g of sand and 1.686 g of calcium chloride. Calculate the percentage of each of the three components recovered from the original mixture and the percent of material lost during the separation process. (4 points)
PRESTUDY (second of two pages)
- Using the physical properties you entered in the table and the outlined experimental procedure, complete the flow chart. In the oval spaces, name the reagents and/or conditions necessary to affect each indicated separation step. In the rectangular boxes, write the names of the separated components. (2 points)
Mixture of NaCl, SiO 2 , NH 4 Cl
SiO 2 and NaCl NH 4 Cl vapor
heat to 340C
