Chem Lab Final Weeks 1-7

How many moles of NaCl are in 0.58 g of NaCl?

0.0099

The analysis of 1.00 g sample of phosphorous oxide, with a molar mass of about 284 g/mol, was found to contain 0.44 g of phosphorous and 0.56 g of oxygen. Calculate the empirical formula and the molecular formula for this phosphorous oxide.

0.44g P x 1 mol/30.974g =0.0142/0.0142=1 x 2 =2 0.56g O x 1mol/15.999g =0.0350/0.0142=2.5 x 2=5 Empirical Formula= P2O5 Given molar mass/Empirical molar mass= n 2(30.974) + 5(15.999) =141.943 284/141.94=2 (P2O5)2 Molecular Formula= P4O10

For liquid B, you decide to use a 50 mL burette to once again dispense 5.00 mL of liquid B into a convenient container. You find that the empty container has a mass as 3.05 grams. After obtaining the mass of the empty container you place it beneath the burette and open the stopcock valve. Although you try to stop the flow of liquid B at exactly the 5.00 mL mark you overshoot slightly and end up dispensing 5.14 mL. What is the density of liquid B in terms of g/mL?

0.891

You wish to determine the density of two unknown, immiscible liquids, A and B, at room temperature. To do this you must measure the mass of a known volume of each liquid. For liquid A, you decide to use a volumetric pipet to dispense exactly 5.00 mL into a convenient container. Before dispensing the volume of liquid A into the container, you obtain and record the container's mass as 2.83 grams. After adding the 5.00 mL of liquid A to the container you reweigh the liquid containing container and find the combination to have a mass of 7.71-grams. What is the density of liquid A in g/mL?

0.976

You are asked to determine the percentage of the components of a mixture containing sodium iodide, NaI, magnesium hydroxide, Mg(OH)2, and barium sulfate, BaSO4. The total mass of your mixture sample is 4.82g. First you extracted the NaI from the mixture with water and filtered insoluble Mg(OH)2 and BaSO4 from the solution, containing the NaI. After evaporating and drying the filtrate, you find that you have recovered 0.95g of NaI. When you react the insoluble residue of Mg(OH)2 and BaSO4 with 3M HCl, the Mg(OH)2 dissolves. After decanting the supernatant liquid containing aqueous MgCl2 from the insoluble BaSO4 and drying the solid, you recover 2.04g of BaSO4. Finally you add 3M KOH solution to the aqueous solution to precipitate the Mg(OH)2. After filtering thesolution and drying the precipitate, you recovered 1.21g of Mg(OH)2. Calculate the percent NaI in the original sample mixture.

19.7

5.00 g of an organic compound was found to contain 2.73 g of carbon, 0.46 g of hydrogen and 1.81 g of oxygen. What is its empirical formula? If its molar mass is about 88 g/mol, what is its molecular formula?

2.73g C x 1mol/12.011=0.22729/0.11313=2 0.46g H x 1mol/1.008=0.456349/0.11313=4 1.81g O x 1mol/15.999=0.11313/0.11313=1 Empirical Formula-C2H4O Given molar mass/Empirical molar mass = n 2(12.011) +4(1.008) + 15.999= 44.053 88g/mol / 44.053=2 (C2H4O)2 Molecular Formula= C4H8O2

Same and Calculate the percent Mg(OH)2 in the original sample mixture.

25.1

or liquid B, you decide to use a 50 mL burette to once again dispense 5.00 mL of liquid B into a convenient container. You find that the empty container has a mass as 3.05 grams. After obtaining the mass of the empty container you place it beneath the burette and open the stopcock valve. Although you try to stop the flow of liquid B at exactly the 5.00 mL mark you overshoot slightly and end up dispensing 5.14 mL. What is the mass of liquid-B that was dispensed if you continue with the density determination for liquid B and find that the mass of the container plus the 5.14-mL of liquid B is 7.63-grams?

4.58

Calculate the percent BaSO4 in the original sample mixture.

42.3

Calculate the total percent recovery based on the combined masses that were recovered.

87.1

Calculate the mass, in grams, of 0.4 mol of CuSO4 * 5H2O

99.8

A mixture was known to contain three of the four compounds in the table. After the mixture of the three solids was extracted with hot water and filtered, Compound A was obtained by evaporating the filtrate to dryness. When 3M HCl was added to the solid residue, a clear solution resulted. After adding excess 3M NaOH solution to the acid solution, a precipitate was formed. After filtration, the insoluble solid was found to be Compound B. Compound C was recovered by evaporation of the filtrate. None of the compounds (A, B, or C) was soluble in all of the solvents; water, 3M HCl, and 3M NaOH.

Compound A was Benzoic Acid because it is soluble in hot water and so would have been in the filtrate. Compound B was Mg(OH)2 because it is insoluble in NaOH and so would have been the insoluble solid that was filtered out. Compound C was Zn(OH)2 because it is soluble in NaOH and so it would have been in the filtrate in that part of the experiment And none of them could be Na2SO4 because it was soluble in all the solutions.

List four physical methods that can be used to separate mixtures.

Decantation, filtration, evaporation, and extraction.

Why should you be careful when you heat your NaCl solution to evaporate the water?

If the solution is heated too much then it could be dangerous because the liquid could splash out of container and get in your eyes or face. Also the splash would mess up your calculations because you would lose some of the NaCl.

Define empirical formula.

It's the simplest positive integer ratio of the atoms in a compound. Any molecule that can be represented as (CH5N)n has the empirical formula of CH5N.

Which of the two liquids is denser; if combined, which liquid would sink, which would float?

Liquid A is denser so if they were combined, liquid A would sink and liquid B would float.

What do the initials MSDS stand for?

Material Safety Data Sheet

Could you separate the components of a mixture Mg(OH)2 and Zn(OH2) by using 3 M HCL?

No. Since both components of the mixture are soluble in 3 M HCL you would not be able to seperate one out.

Use the information in questions 4 and 5 to calculate the density of the die in terms of grams/cm3. After you have performed the above procedures you notice that the die is NOT a perfect cube, as there are depressions on each side and the edges are rounded. Have you over or under estimated the volume of the die? If you use these values, will you overestimate or underestimate the density of the die? Explain!

Since D=M/V, the density for the dice would equal 2.46g/2.05cm^3. The density of the dice would end up as 1.20 g/cm^3. I have overestimated the volume of the die because I did not take into account the the rounded edges or depressions. Those would make the volume slightly less than I originally calculated. Therefore, the density that I calculated would be slightly underestimated actually because the less I have as the volume of the dice, the less I would be dividing the mass by. Therefore the density would have been slightly higher if I calculated with the new volume that took the depressions and rounded edges into account.

Since the die is a cube its volume can easily be determined by performing a direct, physical measurement of its length using a metric ruler. You find the length of one side of the die to be approximately 1.27cm long. Since the die is a cube, its volume can be estimated as being equal to the length of one of its sides cubed (volume = length of a side3). What is the volume of the cube in cm3.

So the volume of the cube would be 1.27 cm^3 which would look like 1.27x1.27x1.27. This would equal 2.05cm^3

The recovery of CaCO3 was attempted by adding 1M KNO3 solution instead of 1M K2CO3 solution to the filtrate, containing aqueous CaCl2.

The addition of KNO3 will change the process of precipitating the CaCO3. In the reaction, since CaCO3 is reacting with KNO3 instead of K2CO3 the results of the reaction should be different. It would produce a final product of CaNO3 instead of CaCO3 like we wanted. All of the compounds would be soluble in water and so no solid, or precipitate, would form. Therefore, I think that it would affect the experiment in that we would not even end up with the final product that we wanted.

The molecular formula of naphthalene is C10H8. What is its empirical formula?

The empirical formula of naphthalene is C5H4.

For liquid B, you decide to use a 50 mL burette to once again dispense 5.00 mL of liquid B into a convenient container. You find that the empty container has a mass as 3.05 grams. After obtaining the mass of the empty container you place it beneath the burette and open the stopcock valve. Although you try to stop the flow of liquid B at exactly the 5.00 mL mark you overshoot slightly and end up dispensing 5.14 mL.

The expirement should be able to proceed without you having to start over and get the exact measurements. Since the mass of the liquid has not yet been calculated and you know the volume that you have, the density should still be the correct answer. If you are comparing the liquids later on then you may want to get the precise measurement since that is what was used for the other expirement. But that would only be for consistencies sake. The actual density should be the same either way.

You wish to determine the density of a die. you must measure its mass and volume. To measure its mass you use an available balance. you record its mass of 0.55 grams. You estimate the total mass of the dice and weigh boat to be 3.01 grams. What is the mass of the dice?

To calculate the mass of the dice you would have to take the total mass and subtract the mass of the weigh boat. That would be 3.01g-0.55g. So the answer would be 2.46 grams or 2.5 grams when calculated with significant figures.

A mixture of NaCl, SiO2, and CaCO3 is separated following the procedure given in this experiment. Indicate how each of the following procedural changes would affect the amount of the specified substance recovered. Briefly explain. Hint: Refer to Table 1 for Solubility & Reactivity The recovery of CaCO3 was attempted by adding 3M H2SO4 instead of 3M HCl to the SiO2/CaCO3 residue.

When the H2SO4 was added, the CaCO3 would still react and the SiO2 would not react, just like they were supposed to. However, when the CaCO3 reacted it would make CaSO4 instead of CaCl2 which is aqueous. CaSO4 is insoluble in water and so when you decant the liquid to get rid of the SiO2, a larger than normal amount of the CaSO4 would be left behind. Therefore, you would end up with less of the amount of the substance than you should.

Briefly describe how you could separate the components of a mixture of benzoic acid and Na2SO4 and recover the two separated substances

You could separate the components of the mixture by adding cold water. Since Na2SO4 is soluble in it and benzoic acid isn't, you could use filtration to separate the mixture and then evaporate out the water to end up with the two original components.

Which device should be used as a suction device for pipeting liquids?

a pipet

The colors of the chemical safety diamond represent different types of hazards

blue- health hazard, red- fire hazard yellow- instability hazard white- specific hazard

Which of the following items is not appropriate to wear to lab?

can't wear opened toed shoes have to wear pants and goggles

What should you do if you break a glass container in the lab?

clean it up and put any glass in the correct container

What things should you do before leaving the lab?

clean up, dispose of waste

Which informative symbol might you find on a chemical bottle?

hazard communication symbol

It is okay to pipet by mouth so long as the chemical solution is dilute enough to not be hazardous.

it is not. don't do that

It is okay to wear flip-flops in the lab room

it is not. wear close toed shoes only

The chemistry stock room will not rent or loan goggles.

it will do both

Ultimately, who is responsible for your safety while working in this lab?

me

When is it okay to eat something in the lab room?

nevera

It is okay to start an experiment before the instructor ever gets to lab.

no. wait for them

When using a chemical in the lab, you should always:

not spill it on yourself

Which of the following are approved safety goggles for chemistry lab?

ones with the knobs on top. indirect ventilation

What should you do when a very small container of alcohol catches fire in the lab?

put a lid on it

If you get a large quantity of chemicals spilled down your back, you should:

strip down and go to the emergency shower

Which of the following methods would work best for smelling a chemical in lab?

wafting it towards you with your hand

If you spill a small amount of chemical on your hands while transferring the chemical

wash your hands quickly

When is it okay to dispose of laboratory materials down the drain of the lab sinks?

when the professor says it is