what can be used to identify an unknown substance

IDENTIFICATION OF AN UNKNOWN LIQUID (Lab 3)

Observe: Text in black is from the lab manual. Text edition in else colors are additional comments and instructions added. The under paginate is useful for pre-lab, in-lab, and post-lab activities.

Introduction

A substance can be identified by observing its chemical and physical properties.  Physical properties are those that a substance can demo without undergoing a change in chemical report. 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-looking that readily combines with oxygen to form iron (III) oxide. That behavior is a chemical attribute of iron because information technology involves how Fe hindquarters undergo a chemical change. Press melts at 1538°C (2800°F). That is a physical property because it doesn't require iron to undergo a chemical transfer (no other elements combined with information technology nor did it decompose).

The identification of a core past its physical properties is the more worthy method because the try is not destroyed in the determination.  Some of the more common physical properties are:  color, odor, density, solubility, state (solid, fluid, or gas at 20°C[elbow room temperature]), freezing point, simmering point, and index of refraction.  Probably the major difficulty is that in order to influence accurate values, united must cost using a pure substance.  Most materials found in nature are not undefiled. The finally paragraph makes any goody-goody points. The identification of a substance by measuring its physical properties depends on the substance existence pure. Tables that contain physical properties of various substances are assuming information technology is double-dyed. For example, pure piss boils at 100°C; still, if impure with salts or another liquid, the stewing point will not be 100°C. So identifying information technology As water from its boiling point physical property leave not be possible. This is why much of chemistry has to arrange with purifying samples. Once you feature a double-dyed substance, its designation is much easier. Liquids are often purified exploitation distillation. Encounter setup happening the satisfactory for doing that. A variety of liquids leave Be assembled at different temperatures.
In that experimentation you will identify an unknown liquid (a native substance) after mensuration values of the following corporal properties:

• density
• boil
• physical phenomenon index

Measuring concentration will be near the unvaried as you did in the previous science laborator.

Base hit
Many a structured liquids are toxic and flammable, so you should exercise care whenever handling them.  Do not breathe the vapours.  Do not allow unknown liquids to interject contact with your skin.  If this happens flush the area with copious amounts of weewe.
These tips are not only good for working in a chemistry science laborator, but likewise for handling solvents and cleaning solutions around the home plate. Your skin is pretty good at repelling irrigate-based liquids because of the natural oils (sebum) in the bark, simply not-polar essential (C-founded) liquids wish wash these oils and so integrated compounds will pass direct the skin and enter the blood stream. Some first aid for integrated molten shinny exposure not only includes flushing with water simply too applying anti-bacterial creams because skin without these oils is more susceptible to bacteria.

The unknowns are flammable.  Keep them off from all flames.
Connected the right is a photo of a lab fire at Texas Technical school University. A 4 liter bottle of flammable liquid broke. It was in the hood with some good plates, which allow the source of ignition. 6 feet away were astir 100 gallons of other combustible liquids. Fortunately, those did not catch give the axe. To read more nearly the incident visit: http://www.nmsu.edu/safe/news/news-items/TDT-chem-lab-fire2.htm

Equipment

The simmering point in time of the liquid uses a prove tube (25mm wide and about 150mm to 200mm lanky). As wel, you need a rubber show-stopper with a thermometer inserted into one hole and a right-angle bent glass metro inserted in the other hole. Rubber tubing is related to the end of the glassful tubing.

Safety
Do non push or pull the thermometer surgery bended glass to change their perspective. They will easily break if you try to move them.

1. Compactness determination of an unknown liquid

Procedure

The density of a substance is a quantity of its mass per unit volume.  Density units for liquids Crataegus laevigata be graphic as g/mL, g/cm³, or g/cc, but all have the equal definite quantity value.  The tightness of a liquefied will vary with the temperature but this change is usually negligible if the temperature change is small.

Note that instead of putt the volume in the denominator (after /) some sources use a negative exponent and set down a Department of Transportation 'tween the units. So you may see:
g·mL^-1, g·atomic number 96^-3, Beaver State g·cc^-1

Density can also incline in kilograms per kilolitre.

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

The small clash has boiling chips in it. You will want one or two for the stewing point determination.

Weigh a perfect, dry, smaller stoppered Erlenmeyer flask as accurately as possible.

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

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

To review the techniques for using the pipette, the below data link bequeath open up a instructor for victimization a pipette in a new window. Just close that window when finished.

In this lab you don't get enough unknown liquid to rinse off out the pipette. So make reliable your pipette is unarmed and dry before measurement out the 10.00 mL.

Victimization a Pipette Instructor

Substitute the stopper avoiding any contact between the stopper and the liquid. (Some liquids dissolve rubber stoppers. The immature (neoprene) stoppers used Here are many 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 state connected the assonant balance used for the first measuring.
(If a balance is deliberation a miniature high or small, weighing the flaskful on the same balance will cancel that error when subtracting the flaskful weight from the weight of the flaskful and liquid.)

Calculate the sight of the 10.00 mL of uncharted liquid in the flask.  Aim the density of the unknown region to iv 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 pass compounds that have densities far from this empiric value (naturally, you involve to be sure that your tightness determination is accurate).
(Since the volume is deliberate with four significant figures and the calculated dissolved lot will also have four significant figures, you are justified in having four significant figures in the calculated concentration.)

2.  Boil purpose for an unknown liquid

Add approximately 5 mL of an unknown liquid to a 25 x 200 millimetre Pyrex mental testing tube.  A boiling chip may be added to the liquid in the test subway to avoid bumping or uneven stewing of the liquid.

This boiling chip is black. Sometimes they are whiteness. They are an inert material that ordinarily is porous, which gives many sites for the liquid to beginner their change from liquid to gas (to boil). They visit these sites nucleation sites. The test tubes used in this science laborator are not always 200 mm tall. Some are a bit shorter.

Approximate the test tube with a rubber stopper fitted with a thermometer and a right–angle glass tube.

Run the gumshoe hose from the unerect glass tube into the sink to keep flammable vapors away from the Bunsen burner. Below is the boiling point setup diagram shown in the research laboratory manual.

Adapt the liquid level so that the thermometer lightbulb is about 1 Cm above the surface of the liquified. Do non attempt to slide the thermometer in the stopple; it will damp!

In other words you want to achieve the 1 cm distance past adding or removing your anon. unfrozen rather than sliding the thermometer up or down.

Support a 400 cubic centimeter beaker one-half-wide-cut of water on an atomic number 26 ring and a wire gauze.  Clamp the test subway system to a ring stand.  The run electron tube should glucinium immersed in the beaker of H2O sol that the unknown liquid is below the water line but the thermometer bulb is above the water level.  Utilization care to assure that the thermometer does non touch the inside of the test tube-shaped structure and the test tube does not come in middleman with the beaker.  See Figure 3.1.

Heating the liquid in the test tube by heating a beaker with water provides a practically more equal heating of the terra incognita melted than heating the test tube directly with the Bunsen burner. Using water in the beaker works because the unknown liquids in this experiment boil downstairs the boiling point of water. If the unknown liquids had boiling points higher than water, they would never boil because the boiling pee would prevent the water from going away over 100°C.  In that case you would utilise oil in the beaker because its much higher boiling point. The oil will still hand out the fire u evenly around the unknown semiliquid in the test tube.

To light a Robert Wilhelm Bunsen burner, first light the match then sex the gasoline. If you turn on the gas first, past thither bequeath be a work up of gas roughly the barrel of the Bunsen burner causing a big flash of flames.

Bring the match towards the Bunsen burner from an inch just about down the stairs the barrel. That manner when the burner lights, your fingers will be below the flame up.

Heat the beaker of water gradually.

If the water gets too hot, it may cause the unknown liquid to furuncle so rapidly that most of it may address vaporisation and exit through the rubber tubing. Also, overheating will cause a high reading for the stewing point.

On this small black stewing chip you can see itty-bitty bubbles rising. Your liquid has started to boil.

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

If you wish to recheck this boiling point temperature, allow the water-tub temperature to fall until the unknown liquid Chicago boiling, past reheat the beaker of urine.  Again, using this empiric boiling point note value, eliminate unmapped possibilities that have boiling points far from this ambitious value.  See Table 3.1 on a lower floor.

Personify sure to read the thermometer correctly. This one is just under 63°C or approximately 62.8°C. 3.  Refractive power determination for an unknown liquid.

Deflexion is responsible for the bent spoon effect ascertained when a spoon is partially submerged in water.  Refractive index measurements bottom comprise used to learn solution concentrations, ascertain purity and identify a compound.

Deflective index is also called Refractive index.

The indicant of refraction, expressed as n_D ²⁰, is the ratio of light's velocity in a vacuum to the variable speed of light through a medium.  The number 20 represents the Celsius temperature of the sample while D represents the colorful D line of the sodium spectrum.  The refractive index number of a substance changes if the temperature changes, operating theater if the color of the luminousnes used changes.
Below is the D line of reasoning of sodium's spectrum. When sodium in sodium chloride (NaCl) is placed in a flame, IT creates a bright sensational flame. That is mostly coming from the D line.

The illustration on the right shows how bioluminescent incoming a thawed will slow down. That essentially changes its direction. The angle in the liquid is less than and then the angle it was traveling in front entering the disposable. The sine of those angles are the horizontal lines (forward gilt arrows are length of 1). These horizontal lines are proportional to the amphetamine of light traveling before and after entering the musical. If you divide transgress(θ₂) into wickedness(θ₁), it tells you how much quicker light travels in a vacuum compared to its pep pill in the liquid. That is the index of refraction of that disposable. You can see to it that the more the light slows polish, the smaller hell(θ₂) becomes. That makes the index of refraction higher, because that smaller sin(θ₂) will divide into sin(θ₁) more times.

Before making a physical phenomenon index measurement of the unknown liquid, your instructor should brief you along the proper operating procedure for the refractometer.  Incoming, for practice session, determine the deflective index of distilled pee.  When you are confident, determine the index of refraction of your unsuspected liquid.  The refractile index should be read to at least four decimal fraction places.

The index of refraction (index of refraction) for water is 1.3330. Put differently, light travels 1 and 1/3 times faster in a hoover (or air) than it does in water.

For general instructions for using the refractometer, go through the favourable panels.

This is an Abbe eccentric refractometer. Ernst Abbe worked for the Zeiss Company in Germany in the late 1800's. He reinforced a twist that sandwiched liquid (operating theater transparent solids) 'tween two prisms.

Connected the front end of the refractometer is the mode selector telephone dial. Make sure IT is set to n_D, which agency it will read out the index of refraction (n) exploitation the D line of sodium's spectrum.

The BRIX setting is for measuring the concentration of sugar in water. The wine, beer, moolah, juice, and honey industries utilize this mensuration. The BX-TC is the equal arsenic BRIX except Atomic number 43 means Temperature Compensated. So the twist will adapt the index of refraction based on the temperature of the sample.

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

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.

Place distilled water onto the bottom prism surface. You can usage an eye dropper or fair-and-square pour a bit onto the surface.

Wreak the top prism down and door latch into place complete the bottom optical prism. The liquid is now sandwiched between the prisms. Adjust the light source to better illuminate the disposable.

1. Do secure the crosshair adjustment memory access cakehole is at the six o'clock position (bottom).

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

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

4. Rotate the dispersion discipline cycle to eradicate any red or green colour at the edge of the shadow line.

5. Deform the accommodation keep in line to center the dark line to the crosshair. The shadow line must be perfectly centralised to find an accurate reading.|

6. Press the READ button to read the refractive index. Record that on the data bed sheet. The value of the test sample will personify digitally indicated in the show window above the READ button. Criminal record that on the Data Sheet as the observed index of refraction (n_D ^T )

This is the view through the eye piece. The shadow is the dark region. The crosshairs align with the edge of the phantom. 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 n_D ²⁰ (temperature at 20°C). The n_D ²⁰ values are what are listed in the index of refraction tables, so you must adjust the index of deflection reading material to compensate for temperatures down the stairs or above 20°C. Record the temperature happening the Information Weather sheet.

The Mark Two Abbe Refractometer is equipped with fittings that allow temperature controlled water to pass around the prisms. That can keep the sample distribution 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 high than 20°C.  The n_D values decrease as the temperature rises (n_D is sometimes called "optimal compactness").  To comparison your experimental esteem with the values given in Table 3.1, add 0.00045 for each academic degree above 20°C.  The corrected value of the refractive index is ready-made by victimization the following convention:

For example:  if your measurement  n_D ^T = 1.3323 is ready-made at a temperature T = 24°C, the corrected value is:

Here is the diagram from the users manual for the Check 2 Abbe Refractometer.

Repeat the steps higher up using your unknown liquified. Use Kimwipes to remove any distilled water left on the prism surfaces. When smooth measurement the index of deflexion of your unknown liquid, wipe out it off using a Kimwipe.

Ne'er wipe a dry prism aboveground with a dry Kimwipe. One or the other ought to be wet with a liquid.

Using the information collected for density, boiling point, and refractive index of the unknown liquid identify the unknown liquidity.  Picture Postpone 3.1 below.  If to a greater extent than one unknown or if none of the unknowns agree with your data, then your measurements were non accurate sufficient and should be repeated.

TABLE 3.1. Physical Properties of Some Common Liquids

Volatilisable Liquid Compound	Boil (°C)	Concentration (20°C) (g/mL)	n D 20
methanol [CH3Ohio]	65.0	0.7914	1.3288
ethanol [CH3CH2OH]	78.5	0.7893	1.3611
1-propyl alcohol [CH3CH2CH2OH]	97.4	0.8035	1.3850
2-propyl alcohol [CH3CH2(OH)CH3]	82.4	0.7855	1.3776
methyl radical acetate [CH3-O-C(=O)-CH3]	57.0	0.9330	1.3593
ethyl acetate [CH3CH2-O-C(=O)-CH3]	77.1	0.9003	1.3788
propanone CH3C(=O)CH3	56.2	0.7899	1.355
methyl ethyl group ketone (2-butanone) [CH3C(=O)-CH2CH3]	79.6	0.8054	1.3788
hexane [CH3CH2CH2CH2CH2CH3]	69.0	0.6600	1.3750
urine [H2O]	100.0	0.9972	1.3330

Information Sheet

A.	Density of unknown
	Wt. of Richard August Carl Emil Erlenmeyer flaskful, stopper & unknown	_______	g
	Wt. of Erlenmeyer flask & stopper	_______	g
	Wt. of 10.00 milliliter aliquot of unknown region	_______	g
	Concentration of anon.	_______	g/mL
B.	Boiling point of unknown quantity	_______	°C
C.	Refractive index of liquids

	Temperature at refractometer	n D T (observed)	n D 20 (corrected)
Refractive index of body of water	_______________	_______________	_______________
Physical phenomenon index of undiscovered	_______________	_______________	_______________
D. Identity of unknown liquid: _______________________________

Shade the table under comparing your values with those launch in TABLE 3.1 above.

	Boiling Pt.	Density	n D 20
Found values	_______________	_______________	_______________
True values	_______________	_______________	_______________
If your figures do not agree very well with the true values, give possible reasons.

QUESTIONS

1. Define the following price and give an instance of each.

a. physical property

Example ________________________________________

b. chemical prop

Example ________________________________________

c. stewing point

Instance ________________________________________

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

3. If this try out were conducted in Denver (elevation 5,000 foot.) what would be the upshot on the observed boiling points of the liquids?

4. Which of the following are not physical properties?
Molar mass, concentration, index of refraction, warmth of reaction, heat of vaporization, flammability, freezing point, urine solubility, boiling item

5. If no of your determinations (density, boiling manoeuver, and refractive exponent) agree precisely with the possible unknown values, what is the most likely source of error?

PROBLEMS

(Answers must have the word-perfect number of significant figures and the correct units! You must picture your method acting of solution!)

Problems from Lab Manual

Practice Problems and comments

1. A 10.00 mil volume of stranger liquid was added to a closed Erlenmeyer flask which weighed 48.217 g. If the weight of the unknown liquid plus the stoppered Erlenmeyer flask was 57.056g, compute the tightness of the unsuspected to the correct telephone number of significant figures.? This is a straight forward problem. Flatbottom though the lot of the flask empty and with the liquid were metric to 5 significant figures, what counts is the number after subtracting. For instance, if you had an empty flaskful of 57.001 g and so it weighed 57.056 g with a liquid, the mass of the liquid is 0.055g. That has only 2 significant figures. Luckily, therein trouble, 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 physical phenomenon indicant of 1.3699. What is the virtually likely identity of the unknown? Project Table 3.1. This is where having both density and refractive index number builds sureness. There is one campaigner that is close to the 0.9016 g/mL. That similar liquid likewise has an refractive index that is close to 1.3699. So you are more foreordained of its identity element. Of course, then depends on the liquid being pure. Again, these physical properties reckon on accuracy during measuring.

3. A stoppered bottle, deliberation 38.215 g when looted, weighs 45.362 g when filled with water. When full with an unknown liquid, the bottle and unknown weighs 44.221 g. Work out the liquid's specific sombreness:

s.g = tightness of unknown
density of water

A stoppered nursing bottle that is usually used for determination specific gravity is called the pycnometer. Shown to the left-handed: The word "pycnometer" is from Greek "puknos" significant dim and "meter" meaning to measurement. The pycnometer has a small tube that runs to the top and any excess spills over. When this is filled with both water and alien liquid, the volumes are kept very private to each former. Because the volumes are the same, the volumes will wipe out in the ad hoc gravity formula. That means you put on't even pauperization to know the volume. For example, compactness of the unknown is its mass divided by its volume, and let's visit the volume "V". Density of water is its mass divided by the unvarying volume, V. So we get
specific soberness = mass unknown
        V
mass water
V
What happens is both of the "V's" cancels out, and you are left with:

s.g. = lot unknown
mass water

If mass is in grams (or anything else), the units of mass will cancel. So specific solemnity has atomic number 102 units. It is simply how umteen multiplication more impenetrable the unknown is compared to water. It's honourable their relative concentration (which is another name for specific gravity). Since you know the denseness or piss 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 exchange the value. So a ad hoc gravity of 1.45 has the denseness of 1.45 g/milliliter (OR close-knit to it).

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

	A	B	C	D	E
1	wad bottle + unk liquid	95.167	g
2	- mass empty bottle	67.436	g
3	mass of unk liquid	27.731	g
4
5	mass nursing bottle + water	98.124	g
6	- mass empty bottle	67.436	g
7	whole sle of water	31.688	g
	Specific gravity =	27.731	g unknown	=0.8751 (note: grams cancel)
		31.688	g water

Since the specific gravity is 0.8751, the density is 1.0 g/mL multiplication that. So the compactness is 0.88 g/mil (note we can only use up 2 epoch-making 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 aside 0.99821 g/c, we can keep each 4 operative figures and report density of 0.8735g/mL. Bill: In the lab manual problem, they are entirely wanting circumstantial sobriety.

4. What unsuspected melted 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 ascertain the formula. You need to remember how to do information technology. From freeze to boiling, the Centigrade 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 scurf the addition 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 time value of 139 smaller. So multiplying aside 5/9 will do that. I generate the do of 77.2°C. Now it's easy to consult the melted.

Tip: When you need to type the degree symbol (°), maintain behind the "AL" paint and type 248 on the 10-key pad. When you release the "alt" significant, the ° symbol will appear. I know this plant on Windows computers. IT might work 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. Forward the erroneous belief in this experiment is not greater than 0.1%, which of the liquids listed in Table 3.1 have densities that are within experimental erroneousness (+/- 0.1%) of the denseness determined? Justify your answer.

c. If the error in this experiment is non greater than 1.0%, which of the liquids are inside experimental error (+/- 1.0%) of the density observed? 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 steady need a calculator. Noticed I kept it to 4 monumental figures.

5b) This is pretty straightforward. Bring on 0.1% of 0.8000 g/mL. That privy be done without a calculator as well. That's 0.001 x 0.8000g/mL. We just need to move the decimal guide 3 places to the left. Thus that's a range from (0.8000g/mL + 0.0008g/mL) to (0.8000g/mL - 0.0008g/cubic centimetre). 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. Subscribe 1% (0.01) of 0.8000g/c. Then summate it and subtract that amount from 0.8000g/mL. See if any of the liquids on the Mesa are within that range.

what can be used to identify an unknown substance

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