A bunch of questions

[clowsui]

My first post here...and I'm asking questions. I feel kind of like an ingrate for not participating and instantly demanding x_x

 

But no matter...could I have some assistance with the following 6 problems? The help is VERY much appreciated as this is a summer assignment for a class next year and it's worth a lot of points, I think. Also, I have all the answers to the problems but I need to know how to solve them/get some hints on how to solve them.

 

1. Calculate the specific heat of water in units of kcal/lb*degF. (Given information: Specific healt of water = 1.00 cal/g*decC; 1 lb = 454 g, deg C = 5/9F - 32)

 

2. What mass of sodium nitrate is required to produce 5.00 L of oxygen gas according to the following reaction if there is a 78.4% yield?

(Given information: density of O2 = 1.43 g/L; 2NaNO3---> 2NaNO2 + O2)

 

3. A 3.113 g sample of cementite was heated in air producing 4.153 g of Fe2O3. The CO2 gas, another product of the reaction, escaped. What is the empirical formula of cementite?

 

4. Reaction of rhenium metal w/ Re2O7 gives a solid of metallic appearance which conduts electricity almost as well as copper. A 0.788 g sample of this material, which contains only rhenium and oxygen, was oxidized in an acidic solution of hydrogen peroxide. Addition of an excess of KOH gave 0.973 g of KReO3. What is the equation for the reaction of Re with Re2O7?

 

5. What mass of a sample that is 98.0% sulfur would be required in the production of 75.0 kg of H2SO4 by the following reaction sequence?

S8 + 8O2 -> 8SO2

2SO2 + O2 -> 2 SO3

SO3 + H2O -> H2SO4

 

Thanks so much and I hope you have fun helping me out

[swansont]

1. Calculate the specific heat of water in units of kcal/lb*degF. (Given information: Specific healt of water = 1.00 cal/g*decC; 1 lb = 454 g, deg C = 5/9F - 32)

 

This is just unit conversion. You need to convert cal to kcal, C to F and g to lb. (When converting C to F you don't care about the offset between them, because your interested in the change in temperature)

 

For example you can multiply by [math]\frac{1 lb}{454 g}[/math] (or the inverse) because the two values are equal, so it's equivalent to multiplying by 1.

[DeanK2]

All the questions require short steps and I hope you will figure them out. However, for each question a small aid is usually beneficial. I have completed each question, so if you post your results after, it would maybe be helpful. To really do you justice, I have outlined how to complete each question with no exact answers.

 

[hide]1.) This really is just a unit conversion question.

 

2.) O2 has a density value given. Simply multiply (by 5), giving the mass in grams of the oxygen evolved (specified in question). Use moles of O2 =(mass (g)/atomic mass). Multiply by 2 for the moles of sodium nitrate. Following this, multiply by the atomic mass of sodium nitrate (85). This is 78.4% of the value for the grams of sodium nitrate originally. To obtain the theoretically minimum mass of sodium nitrate, simply divide by 78.4 and multiply by 100. Your answer will be close to 100 grams, yet to help you, I have not given an exact answer.

 

3.) The question requires knowledge of an empiracle formula - assuming you are aware of an empiracle formula (the simplest ratio of elements in a compund), it would be quite a good question. As a greater mass of iron (III) oxide than cementite has been created it is logical that this came from oygen in the air.

Unfortunately, the ratio of iron (III) oxide: carbon dioxide is not given. An equation like this: (m)O2 + (n)X --> (o)FE2O3 + (p)CO2, were m,n,o,p are constants representing the moles , cannot be set up. This means the empiracle CANNOT be found with this little information.

 

4.) See question 2 and 5, as both of these methods are needed. This question contains irrelevant information - such as comparison with copper and so forth. However, the question does allow you to work backwards and find the moles of each substance in question.

 

5.) This is just a percentage purity problem. Work backwards from sulfuric acid, in simple steps.

I.E: moles=(mass (g)/relative atomic mass) = (75000/98) = 765.306. This is the same amount of moles of SO3 in the reaction SO3 + H2O --> H2SO4. The moles of SO3 can be used to work backwards. However, do not be tempted to times this number by 2, just because 2SO2 + O2 --> 2 SO3 has a 2 in front of SO3, and the equation to make sulfuric acid does not. Remember that the equations only show the ratio of each molecule or substance with respect to another, while the moles represent an actual amount of the substance.

Once a value for the moles of Sulfur has been found, multiply by 32, its atomic mass. Then remember to divide by 98 and multiply by 100.[/hide]

Edited June 17, 2008 by swansont

[swansont]

I've "hidden" the answers; the goal in HW help is to help, not do the problems — that generally has little benefit. The poster hasn't responded in 10 days, which makes one wonder if they found a sucker somewhere else to do the problems for them.

[Ladeira]

I've "hidden" the answers; the goal in HW help is to help, not do the problems — that generally has little benefit. The poster hasn't responded in 10 days, which makes one wonder if they found a sucker somewhere else to do the problems for them.

 

We all know it (and getting tired of it). But don't get nervous. Be positive

lol

[clowsui]

Sorry guys ^^; I was busy doing an English essay for a few weeks but now I'm back to find out that my questions have been answered.

 

For that cementite question the answer is Fe3C...which doesn't make sense if it's iron (iii). Should I just conclude that I can't answer this question?

 

EDIT: I'm still stuck on these, by the way. Don't be such a cynic

Edited July 2, 2008 by clowsui