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Note: Text in black is from the lab manual. Text in other colors are additional comments and instructions added. The below page is useful for pre-lab, in-lab, and post-lab activities.


A substance can be identified by observing its chemical and physical properties.  Physical properties are those that a substance can exhibit without undergoing a change in chemical composition. Chemical properties are those that a substance exhibits only by undergoing a change in chemical composition (i.e. a chemical reaction).

Example: Iron is a metal that readily combines with oxygen to form iron (III) oxide. That behavior is a chemical property of iron because it involves how iron can undergo a chemical change. Iron melts at 1538°C (2800°F). That is a physical property because it doesn't require iron to undergo a chemical change (no other elements combined with it nor did it decompose).

molten iron

The identification of a substance by its physical properties is the more desirable method because the sample is not destroyed in the determination.  Some of the more common physical properties are:  color, odor, density, solubility, state (solid, liquid, or gas at 20°C[room temperature]), melting point, boiling point, and refractive index.  Probably the major difficulty is that in order to determine accurate values, one must be using a pure substance.  Most materials found in nature are not pure. The last paragraph makes some good points. The identification of a substance by measuring its physical properties depends on the substance being pure. Tables that contain physical properties of various substances are assuming it is pure. For example, pure water boils at 100°C; however, if contaminated with salts or another liquid, the boiling point will not be 100°C. So identifying it as water from its boiling point physical property will not be possible. This is why a lot of chemistry has to do with purifying samples. Once you have a pure substance, its identification is much easier. Liquids are often purified using distillation. See setup on the right for doing that. A mixture of liquids will be collected at different temperatures.
In this experiment you will identify an unknown liquid (a pure substance) after measuring values of the following physical properties:

  • density
  • boiling point
  • refractive index

Measuring density will be almost the same as you did in the previous lab.

fractional distillation
Many organic liquids are toxic and flammable, so you should exercise care whenever handling them.  Do not breathe the vapors.  Do not allow unknown liquids to come in contact with your skin.  If this happens flush the area with copious amounts of water.
These tips are not only good for working in a chemistry lab, but also for handling solvents and cleaning solutions around the home. Your skin is pretty good at repelling water-based liquids because of the natural oils (sebum) in the skin, but non-polar organic (carbon-based) liquids will wash away these oils and so organic compounds will pass through the skin and enter the blood stream. Some first aid for organic liquid skin exposure not only includes flushing with water but also applying anti-bacterial creams because skin without these oils is more susceptible to bacteria.

The unknowns are flammable.  Keep them away from all flames.
On the right is a photo of a lab fire at Texas Tech University. A 4 liter bottle of flammable liquid broke. It was in the hood with some hot plates, which provide the source of ignition. 6 feet away were about 100 gallons of other flammable liquids. Fortunately, those did not catch fire. To read more about the incident visit:  http://www.nmsu.edu/safety/news/news-items/tt-chem-lab-fire2.htm

lab fire

The boiling point of the liquid uses a test tube (25mm wide and about 150mm to 200mm tall). Also, you need a rubber stopper with a thermometer inserted into one hole and a right-angle bent glass tube inserted in the other hole. Rubber tubing is attached to the end of the glass tubing.

Do not push or pull the thermometer or bent glass to change their position. They will easily break if you try to move them.

1. Density determination of an unknown liquid  


The density of a substance is a measure of its mass per unit volume.  Density units for liquids may be expressed as g/mL, g/cm3, or g/cc, but all have the same numerical value.  The density of a liquid will vary with the temperature but this change is usually negligible if the temperature change is small.

Note that instead of putting the volume in the denominator (after /) some sources use a negative exponent and place a dot between the units. So you may see:
g·mL-1, g·cm-3, or g·cc-1

Density can also be given in kilograms per cubic meter.

Pickup your unknown liquid. Each one has a unique number. Write the number on the Data Sheet on page 19.

The small jar has boiling chips in it. You will need one or two for the boiling point determination.


Weigh a clean, dry, small stoppered Erlenmeyer flask as accurately as possible. 

Use the technique from the density lab which says to handle the flask with a paper towel because fingerprints will alter the mass of the flask. Also, follow the other techniques used in the density lab as far as using the analytical balance.

Weight flask

Pipet 10.00 mL of the unknown liquid into the Erlenmeyer flask. 

To review the techniques for using the pipette, the below link will open up a tutorial for using a pipette in a new window. Just close that window when finished.

In this lab you don't have enough unknown liquid to rinse out the pipette. So make sure your pipette is clean and dry before measuring out the 10.00 mL.

Using a Pipette Tutorial


Replace the stopper avoiding any contact between the stopper and the liquid. (Some liquids dissolve rubber stoppers. The green (neoprene) stoppers used here are more resistant to solvents, but getting an unknown liquid on the stopper should be avoided from that standpoint and the fact that you could loose some of the mass of the liquid from evaporation off the sides of the stopper.)

Weigh the Erlenmeyer flask, stopper and added liquid on the same balance used for the initial measurement.
(If a balance is weighing a little high or low, weighing the flask on the same balance will cancel that error when subtracting the flask weight from the weight of the flask and liquid.)

Calculate the mass of the 10.00 mL of unknown liquid in the flask.  Calculate the density of the unknown to four significant figures.  This is necessary since many of the unknown liquids in Table 3.1 have very similar densities. Once the density has been calculated, try to eliminate compounds that have densities far from this experimental value (of course, you need to be sure that your density determination is accurate).
(Since the volume is measured with four significant figures and the calculated liquid mass will also have four significant figures, you are justified in having four significant figures in the calculated density.)

weight liquid
2.  Boiling point determination for an unknown liquid

Add approximately 5 mL of an unknown liquid to a 25 x 200 mm pyrex test tube.  A boiling chip may be added to the liquid in the test tube to avoid bumping or uneven boiling of the liquid. 

This boiling chip is black. Sometimes they are white. They are an inert material that usually is porous, which gives many sites for the liquid to initiate their change from liquid to gas (to boil). They call these sites nucleation sites. The test tubes used in this lab are not always 200 mm tall. Some are a little shorter.

5mL in test tube
Close the test tube with a rubber stopper fitted with a thermometer and a right–angle glass tube.  Insert rubber stopper onto test tube

Run the rubber hose from the bent glass tube into the sink to keep flammable vapors away from the Bunsen burner. Below is the boiling point setup diagram shown in the lab manual. 
boiling point setup


Run rubber hose to sink

Adjust the liquid level so that the thermometer bulb is about 1 cm above the surface of the liquid.  Do not attempt to slide the thermometer in the stopper; it will break!

In other words you want to achieve the 1 cm distance by adding or removing your unknown liquid rather than sliding the thermometer up or down.

5mL in test tube with thermometer

Support a 400 mL beaker half-full of water on an iron ring and a wire gauze.  Clamp the test tube to a ring stand.  The test tube should be immersed in the beaker of water so that the unknown liquid is below the water level but the thermometer bulb is above the water level.  Use care to assure that the thermometer does not touch the inside of the test tube and the test tube does not come in contact with the beaker.  See Figure 3.1.

Heating the liquid in the test tube by heating a beaker with water provides a much more even heating of the unknown liquid than heating the test tube directly with the Bunsen burner. Using water in the beaker works because the unknown liquids in this experiment boil below the boiling point of water. If the unknown liquids had boiling points higher than water, they would never boil because the boiling water would prevent the water from going over 100°C.  In that case you would use oil in the beaker because its much higher boiling point. The oil will still distribute the heat evenly around the unknown liquid in the test tube.

beaker on stand with test tube in it. Test tube held by clamp

To light a Bunsen burner, first light the match and then turn on the gas. If you turn on the gas first, then there will be a build up of gas around the barrel of the Bunsen burner causing a big flash of flames.

Bring the match towards the Bunsen burner from an inch or so below the barrel. That way when the burner lights, your fingers will be below the flame.

Turn on gas

Heat the beaker of water gradually. 

If the water gets too hot, it may cause the unknown liquid to boil so rapidly that most of it may turn to vapor and exit through the rubber tubing. Also, overheating will cause a higher reading for the boiling point.

Run rubber hose to sink


On this small black boiling chip you can see small bubbles rising. Your liquid has started to boil.

boiling at boiling chip

Record the temperature at which the liquid in the test tube boils freely, then remove the burner.  In addition to boiling freely, look at the top of the test tube for condensation on the glass tubing. That means your unknown liquid has been boiling sufficiently to send vapors to the top of the test tube. That also means the thermometer has probably reached the boiling point of the unknown liquid. Now you can read the thermometer to get the boiling point of your unknown liquid.

If you wish to recheck this boiling point temperature, allow the water-bath temperature to fall until the unknown liquid stops boiling, then reheat the beaker of water.  Again, using this experimental boiling point value, eliminate unknown possibilities that have boiling points far from this determined value.  See Table 3.1 below.


Condensation on glass tube at top
Be sure to read the thermometer correctly. This one is just under 63°C or about 62.8°C. thermometer reading 63 degrees
3.  Refractive index determination for an unknown liquid.  

Refraction is responsible for the bent spoon effect observed when a spoon is partially submerged in water.  Refractive index measurements can be used to determine solution concentrations, ascertain purity and identify a compound. 

Refractive index is also called Index of Refraction.

bent spoon due to refraction

The index of refraction, expressed as nD20, is the ratio of light’s velocity in a vacuum to the variable velocity of light through a medium.  The number 20 represents the Celsius temperature of the sample while D represents the monochromatic D line of the sodium spectrum.  The refractive index of a substance changes if the temperature changes, or if the color of the light used changes.
Below is the D line of sodium's spectrum. When sodium in sodium chloride (NaCl) is placed in a flame, it creates a bright yellow flame. That is mostly coming from the D line.

sodium's sprectrum with d-line pointed out

The illustration on the right shows how light entering a liquid will slow down. That essentially changes its direction. The angle in the liquid is less than then the angle it was traveling before entering the liquid. The sine of those angles are the horizontal lines (assuming gold arrows are length of 1). These horizontal lines are proportional to the speed of light traveling before and after entering the liquid. If you divide sin(θ2) into sin(θ1), it tells you how much faster light travels in a vacuum compared to its speed in the liquid. That is the index of refraction of that liquid. You can see that the more the light slows down, the smaller sin(θ2) becomes. That makes the index of refraction higher, because that smaller sin(θ2) will divide into sin(θ1) more times.

index of refraction illustration

Before making a refractive index measurement of the unknown liquid, your instructor should brief you on the proper operating procedure for the refractometer.  Next, for practice, determine the refractive index of distilled water.  When you are confident, determine the refractive index of your unknown liquid.  The refractive index should be read to at least four decimal places.

The refractive index (index of refraction) for water is 1.3330. In other words, light travels 1 and 1/3 times faster in a vacuum (or air) than it does in water.

For general instructions for using the refractometer, see the following panels.


This is an Abbe type refractometer. Ernst Abbe worked for the Zeiss Company in Germany in the late 1800's. He built a device that sandwiched liquid (or transparent solids) between two prisms.

On the front of the refractometer is the mode selector dial. Make sure it is set to nD, which means it will read out the index of refraction (n) using the D line of sodium's spectrum.

The BRIX setting is for measuring the concentration of sugar in water. The wine, beer, sugar, juice, and honey industries utilize this measurement. The BX-TC is the same as BRIX except TC means Temperature Compensated. So the device will adjust the index of refraction based on the temperature of the sample.

In veterinary medicine a refractometer is used to measure blood plasma protein. Gemologists use refractometry to identify gems.

Refractometer dial
At the back of the refractometer are the two prisms. You lift up the top prism to see the faces of both prisms. The sodium lamp is the light source. Refractometer opened showing 2 prisms

Place distilled water onto the bottom prism surface. You can use an eye dropper or just pour a little onto the surface.


pour liquid onto refractometer

Bring the top prism down and latch into place over the bottom prism. The liquid is now sandwiched between the prisms. Adjust the light source to better illuminate the liquid.

adjust light on refractometer

1. Make sure the crosshair adjustment access hole is at the six o’clock position (bottom).

2. Rotate the eyepiece to bring the crosshair into focus. (See image below for view of crosshairs)

3. Move the shadow line to the crosshair with the coarse adjustment control. (See image below for view of crosshairs and shadow line)

4. Rotate the dispersion correction wheel to eliminate any red or green color at the edge of the shadow line.

5. Turn the adjustment control to center the shadow line to the crosshair. The shadow line must be perfectly centered to obtain an accurate reading.|

6. Press the READ button to read the index of refraction. Record that on the data sheet. The value of the test sample will be digitally indicated in the display window above the READ button. Record that on the Data Sheet as the observed index of refraction (nDT)

Labeled refractometer
This is the view through the eye piece. The shadow is the dark area. The crosshairs align with the edge of the shadow. cross hairs
7. Depressing the TEMP button will activate a temperature sensing device located in the measuring prism. The display will digitally indicate the actual temperature of the measuring prism and sample. You need the temperature to calculate the index of refraction for nD20 (temperature at 20°C). The nD20 values are what are listed in the index of refraction tables, so you must adjust the index of refraction reading to compensate for temperatures below or above 20°C. Record the temperature on the Data Sheet. Push temperature button on Refractometer

The Mark II Abbe Refractometer is equipped with fittings that allow temperature controlled water to pass around the prisms. That can keep the sample at 20°C which eliminates the need to make adjustment calculations to the index of refraction. Since the laboratory is not equipped with a constant temperature bath, the temperature of the refractometer will probably be higher than 20°C.  The nD values decrease as the temperature rises (nD is sometimes called “optimal density”).  To compare your experimental value with the values given in Table 3.1, add 0.00045 for each degree above 20°C.  The corrected value of the index of refraction is made by using the following formula:

temperature correction formula
For example:  if your measurement  nDT = 1.3323 is made at a temperature T = 24°C, the corrected value is:

Temperature calculation at 24 degrees

water ports on refractometer

Here is the diagram from the users manual for the Mark II Abbe Refractometer.

Repeat the steps above using your unknown liquid. Use Kimwipes to remove any distilled water left on the prism surfaces. When finished measuring the index of refraction of your unknown liquid, wipe it off using a Kimwipe.

Never wipe a dry prism surface with a dry Kimwipe. One or the other ought to be wet with a liquid.


diagram of Mark II Abbe Refractometer
Using the data collected for density, boiling point, and refractive index of the unknown liquid identify the unknown liquid.  See Table 3.1 below.  If more than one unknown or if none of the unknowns agree with your data, then your measurements were not accurate enough and should be repeated.
TABLE 3.1. Physical Properties of Some Common Liquids
Volatile Liquid Compound
Boiling Point (°C)
Density (20°C) (g/mL)
methanol [CH3OH]
ethanol [CH3CH2OH]
1-propanol [CH3CH2CH2OH]
2-propanol [CH3CH2(OH)CH3]
methyl acetate [CH3-O-C(=O)-CH3]
ethyl acetate [CH3CH2-O-C(=O)-CH3]
acetone CH3C(=O)CH3
methyl ethyl ketone (2-butanone) [CH3C(=O)-CH2CH3]
hexane [CH3CH2CH2CH2CH2CH3]
water [H2O]
Data Sheet
Density of unknown    
  Wt. of Erlenmeyer flask, stopper & unknown
  Wt. of Erlenmeyer flask & stopper
  Wt. of 10.00 mL aliquot of unknown
  Density of unknown
Boiling point of unknown
Refractive index of liquids    
Temperature at





Refractive index of water
Refractive index of unknown


D. Identity of unknown liquid: _______________________________


Fill in the table below comparing your values with those found in TABLE 3.1 above.
Boiling Pt.



Found values
True values


If your figures do not agree very well with the true values, give possible reasons.


1. Define the following terms and give an example of each.

a. physical property

Example ________________________________________

b. chemical property

Example ________________________________________

c. boiling point

Example ________________________________________

2. In this experiment, it is important to keep the flask in which you weigh your density sample stoppered except when you are adding liquid to it Why?


3. If this experiment were conducted in Denver (elevation 5,000 ft.) what would be the effect on the observed boiling points of the liquids?


4. Which of the following are not physical properties?
Molar mass, density, refractive index, heat of reaction, heat of vaporization, flammability, melting point, water solubility, boiling point


5. If none of your determinations (density, boiling point, and refractive index) agree exactly with the possible unknown values, what is the most likely source of error?



(Answers must have the correct number of significant figures and the correct units! You must show your method of solution!)
Problems from Lab Manual
Practice Problems and comments
1. A 10.00 mL volume of unknown liquid was added to a stoppered Erlenmeyer flask which weighed 48.217 g. If the weight of the unknown liquid plus the stoppered Erlenmeyer flask was 57.056g, calculate the density of the unknown to the correct number of significant figures.? This is a straight forward problem. Even though the mass of the flask empty and with the liquid were measured to 5 significant figures, what counts is the number after subtracting. For example, if you had an empty flask of 57.001 g and then it weighed 57.056 g with a liquid, the mass of the liquid is 0.055g. That has only 2 significant figures. Fortunately, in this problem, the mass difference will have 4 significant figures. That matches the significant figures of the volume of 10.00 mL.
2. An unknown sample was found to have a density of 0.9016 g/mL and a refractive index of 1.3699. What is the most probable identity of the unknown? See Table 3.1. This is where having both density and refractive index builds confidence. There is one candidate that is close to the 0.9016 g/mL. That same liquid also has an index of refraction that is close to 1.3699. So you are more certain of its identity. Of course, then depends on the liquid being pure. Again, these physical properties depend on accuracy during measurement.

3. A stoppered bottle, weighing 38.215 g when empty, weighs 45.362 g when filled with water. When filled with an unknown liquid, the bottle and unknown weighs 44.221 g. Calculate the liquid's specific gravity:

s.g = density of unknown
           density of water


A stoppered bottle that is usually used for finding specific gravity is called the pycnometer. Shown to the left: The word "pycnometer" is from Greek "puknos" meaning dense and "meter" meaning to measure. The pycnometer has a small tube that runs to the top and any excess spills over. When this is filled with both water and unknown liquid, the volumes are kept very close to each other. Because the volumes are the same, the volumes will cancel out in the specific gravity formula. That means you don't even need to know the volume. For example, density of the unknown is its mass divided by its volume, and let's call the volume "V". Density of water is its mass divided by the same volume, V. So we get
specific gravity =  mass unknown
                     mass water
What happens is both of the "V's" cancels out, and you are left with:

s.g. = mass unknown
            mass water

If mass is in grams (or anything else), the units of mass will cancel. So specific gravity has no units. It is simply how many times more dense the unknown is compared to water. It's just their relative density (which is another name for specific gravity). Since you know the density or water is 1.0 g/mL, you can simply multiply the specific gravity by 1.0 g/mL and you get the density of the unknown liquid. Multiplying by "1" does not change the value. So a specific gravity of 1.45 has the density of 1.45 g/mL (or close to it).

Practice for 3. You don't have a pycnometer, so you use perfume bottle that has a narrow neck. You first weigh the empty perfume bottle and its mass is 67.436 g. You fill it to the brim with distilled water and the weight is then 98.125 g. You pour out the water and let it dry. Now you pour in your unknown liquid to the same level. Its weight is 95.167 g. What is the specific gravity of this unknown liquid, and what is its density (g/mL)?

mass bottle + unk liquid
- mass empty bottle
mass of unk liquid
mass bottle + water
- mass empty bottle
mass of water
Specific gravity =
g unknown =0.8751 (note: grams cancel)
g water

Since the specific gravity is 0.8751, the density is 1.0 g/mL times that. So the density is 0.88 g/mL (note we can only use 2 significant figures). Water at 4°C has a density of 0.99997 g/mL. At 20°C (room temp), it is 0.99821 g/mL. So using 1.0 g/mL is correct to 2 significant figures. If we multiplied by 0.99821 g/mL, we can keep all 4 significant figures and report density of 0.8735g/mL. Note: In the lab manual problem, they are only wanting specific gravity.

4. What unknown liquid boils at 171°F? The is a simple question. The only challenge is the table is in Celsius and not Fahrenheit. To change Fahrenheit to Celsius, it's not always convenient to go find the formula. You need to remember how to do it. From freezing to boiling, the Celsius scale goes from 0°C to 100°C. However, Fahrenheit starts with 32 and goes to 212. If given Fahrenheit just subtract 32 and then the Fahrenheit values would go from 0 to 180. In our example of starting with 171°F, I would first subtract 32 to get 139. On the Fahrenheit scale the increase is 0 to 180, so that's a lot more degrees than for Celsius which is a 100 degree increase. 180/100 reduces to 9/5. Or 100/180 reduces to 5/9. I know I need to make the Fahrenheit value of 139 smaller. So multiplying by 5/9 will do that. I get the answer of 77.2°C. Now it's easy to look up the liquid.

Tip: When you need to type the degree symbol (°), hold down the "alt" key and type 248 on the 10-key pad. When you release the "alt" key, the ° symbol will appear. I know this works on Windows computers. It might work on Mac, but instead of the "alt" key try the "option" key instead. Note, the number has to be typed on the 10-key pad and not at the top of the keyboard.

5. A 25.00 mL sample of a liquid weighs 20.00 grams.

a. Calculate the density of the liquid.

b. Assuming the error in this experiment is not greater than 0.1%, which of the liquids listed in Table 3.1 have densities that are within experimental error (+/- 0.1%) of the density determined? Justify your answer.

c. If the error in this experiment is not greater than 1.0%, which of the liquids are within experimental error (+/- 1.0%) of the density determined? Justify your answer.

5a) is an easy question. 20.00g/25.00mL is the density. Divide by 5/5 to reduce 20/25 to 4/5 and we can see the answer is 0.8000 g/mL. We didn't even need a calculator. Noticed I kept it to 4 significant figures.

5b) This is pretty straightforward. Take 0.1% of 0.8000 g/mL. That can be done without a calculator as well. That's 0.001 x 0.8000g/mL. We just need to move the decimal point 3 places to the left. So that's a range from (0.8000g/mL + 0.0008g/mL) to (0.8000g/mL - 0.0008g/mL). See if there are any of the liquids in the table that fit in that range.

5c) This can be done without a calculator also. Take 1% (0.01) of 0.8000g/mL. Then add it and subtract that amount from 0.8000g/mL. See if any of the liquids on the Table are within that range.

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