Chemistry - April 2007

The heat of fusion of a compound is 333.6 joules per gram. What is the total number of joules of heat that must be absorbed by a 15.0-gram sample to change the compound from solid to liquid at its melting point?

1304J
168J
420J
5004J

A solution containing 60 grams of NaNO3 completely dissolved in 50. grams of water at 50°C is classified as being

saturated
supersaturated
dilute and unsaturated
dilute and saturated

One hundred grams of water is saturated with NH4Cl at 50°C. According to Table G, if the temperature is lowered to 10°C, what is the total amount of NH4Cl that will precipitate?

5.0 g
17 g
30. g
50. g

how many grams of KNO3 would be needed to saturate 200 grams of water at 70°C?

43 g
86 g
134 g
268 g

2007-04-25 13:41:13 · 1 answers · asked by Celia 4

If a chemistry instructor combines and heats the mixture of iron and sulfur in an open crucible, a chemical reaction takes place and the elements combine to formed iron (II) sulfide, which is not magnetic. First, write an unbalanced equation for this reaction. Then balance it. Finally, calculate the theoretical yield if 5.25 grams of iron is reacted with 6.93 grams of sulfur and the % composition of the newly formed compound. Note: some of the sulfur MIGHT be oxidized into sulfur dioxide in the reaction.

2007-04-25 13:40:19 · 1 answers · asked by Reed 1

1. identify the environmental impact associated with high and low level nuclear wastes.
2. explain how nuclear reactions convert small amounts of matter into a relatively large amount of energy.
3. Compare and contrast the nuclear processes that occur in the sun and stars (fission) as in nuclear reactors(fusion)

HELP AND GIVE ME THE WEBSITES YOU USED<3 :D

2007-04-25 13:25:49 · 1 answers · asked by kitty 2

Consider the molecules NF3, AsF3, SF4, PF3, and CF4.
I need to know which bonds are most polar and which have a molecular dipole moment. Please let me know how you figure this out, thanks.

2007-04-25 13:21:40 · 1 answers · asked by Anonymous

2007-04-25 13:21:01 · 1 answers · asked by lea 1

2007-04-25 13:13:35 · 1 answers · asked by Anonymous

2007-04-25 13:11:15 · 1 answers · asked by Anonymous

percent concentration by mass
molarity
molality
all of the above are used equally

2007-04-25 12:58:27 · 1 answers · asked by Meno 1

I only have 7 left.
Use the periodic table as a word bank and fill in each blank with an element-thanks for all of your help! I appreciate it!
1. To enter a poker game you have to _______.
2. Do you know what I am when I dysprosium?__________
3. To kill bugs on your plants you have to spray some _______
4. We weren't afrais od the Lambkin football tesm so we________
5. "Ring in the Mass" said the Bishop
"But Sire, we have______."
6. At lease I am __________to believe it is very ________.
7. ___________are vanishing___________.

2007-04-25 12:49:12 · 2 answers · asked by Anonymous

Half Cell Reactions ``Standard Electrode Potentials (volts)
K <-> K+ + e- ````````````````+2.92
Ca <-> Ca++ + 2e- ``````````+2.87
Mg <-> Mg++ + 2e- `````````+2.34
Zn <-> Zn++ + 2e- ````````````.762
Cu <-> Cu++ + 2e- `````````-.344
Ag <-> Ag+ + e- `````````````-.7995
Pt <-> Pt++ + 2e- `````````````-1.2

The Choices:

A. Calcium and Silver
B. Copper and Zinc
C. Magnesium and Platinum
D. Potassium and Silver
E. Zinc and Silver

Please let me know why thats the answer also because i don't understand how to solve it.

2007-04-25 12:43:29 · 1 answers · asked by Allie C 1

problem:
determine the pH of a solution that is 3x10 -2 (.03) M HCl

any ideas?

2007-04-25 12:39:14 · 1 answers · asked by gtrman90 1

In the compound you will make today the ammonia ligand uses its ___ electrons to form a bond to the copper ion. (It was Cu+2 and NH3).

The choices that I have are.
a. s
b. p
c. d
d. f
e. anti-bonding
f. Non-bonding

I answered that the electrons were p electrons, but that was incorrect. I need help understand what the answer is and why it is that answer, please. ^-^

2007-04-25 12:16:56 · 3 answers · asked by Gavin M 1

2007-04-25 12:12:26 · 1 answers · asked by osisanya d 1

2007-04-25 12:10:31 · 1 answers · asked by Anonymous

Can anyone explain what happened in this lab? I'm totally confused about the results.

So we did a lab in class today where we collected three test tubes of ethyne gas. One tube was full, one was half full of ethyne gas, and one tube with 1 cm of gas.

We collected the gas by reacting CaC2 in water to collect the ethyne gas, meaning that nothing else should be in the test tubes except for the gas.

When we held a flame near mouth of the FULL tube, there was a small pop and a little bit of residue near the top of the test tube, meaning that it was incomplete combustion.

The half-full tube resulted in ALOT of residue, meaning alot of incomplete combustion.

The 1 cm tube resulted in a very loud pop and no residue (complete combustion).

I was assured that the results are correct, but I can't figure out why the half-full tube left alot of residue, yet the full tube only left a little bit of residue.

Also, how would I write the combustion equations for the half tube and full tube?

2007-04-25 12:09:26 · 3 answers · asked by Dave H 2

Name the alkanes that have the following formulas:

A) CH3CH2CH3

B) CH3(CH2)6CH3

C) C3H8

D) C5H12

2007-04-25 12:06:55 · 3 answers · asked by Africanprincess 2

A student carefully diluted 25.0mL of 6moles/L NaOH solution in 475 mL of distiled water. What is the molarity of the diluted solution base? And why can't the diluted NaOH solution be used as a standard solution of base?


I can't figure this one out. I don't feel like the problem has enough info to solve it.

2007-04-25 11:55:12 · 2 answers · asked by Jennifer R 2

...thermometer

2007-04-25 11:48:34 · 1 answers · asked by Notorious P 1

2007-04-25 11:47:18 · 2 answers · asked by Notorious P 1

2007-04-25 11:46:26 · 1 answers · asked by Notorious P 1

Silver chloride us very insoluble in water, and by adding a very slight excess of silver nitrate, it is possible effectively to remove all the chloride ion from the sample. First, write the balanced net ionic equation for this reaction. Then assume that a sample has a mass of 1.054 grams contains 21.5% chloride ion by mass. Then calculate the mass of silver nitrate that be used to completely precipitate all the chloride from the sample?

2007-04-25 11:34:54 · 2 answers · asked by herlots 1

2007-04-25 11:25:32 · 4 answers · asked by Anonymous

1. If the concentration of oxygen in water is 8ppm, what mass of oxygen is present in 1L of water?
2. A 10% W/V salt solution is used for making pickles. What mass of salt is presnt in 750mL of this solution? (what is the formula i should use!!?!)
can someone explain to me about the ppm (parts per million)?

2007-04-25 11:20:47 · 3 answers · asked by no name 1

A beaker containig Pb(NO3)2. dissolved in water. Than adds a solution of NaI, and a bright yellow precipitate is formed. Then contiues to add NaI until no further yellow precipitate is formed. The person filters the precipitate, dries it in an oven, and finds the mass of 1.43g.
Use a balanced chemical equation to determine what mass of lead nitrate Pb(NO3)2 was dissolved in the water in the beaker.

2007-04-25 11:20:09 · 1 answers · asked by Anonymous

What is the half-life in minutes of a radioactive nuclide if 1 ⁄ 32nd of the original sample remains after 18.0 min ?

Enter a numeric answer only do not include units

2007-04-25 11:17:50 · 3 answers · asked by sera 1

How long will it take for 52.0% of a 0.00530 mg sample of radioactive iron-59 to decay? The half-life of iron-59 is 45.10 days, so give your answer in days.

Enter a numeric answer only do not include units

2007-04-25 11:16:21 · 1 answers · asked by sera 1

I answered EVERY single question on my homework (all 14 of them) and I've been trying to do this one question for 4 days!!! Please help me!!!!

Here's the evil question...:

You notice that there are deposits of calcium carbonate (a hard white-colored substance) along the inside walls of the swimming pool. What do you think caused this? Describe in detail, including the reaction type (if any), and what the calcium carbonate is called.


Thank you!! Thank you!!

2007-04-25 10:56:38 · 2 answers · asked by Anonymous

2007-04-25 10:56:37 · 1 answers · asked by tq 3

3-Bromopentane reacts with OH- to give 2-pentene. Which of the following
statements are true?



a) 3-Bromopentane is a Lewis base in this reaction

b) Hydroxide ion is a Bronsted base in this reaction

c) The byproduct of this reaction is Br2

d) Br- anions are produced in this reaction

e) One mole of 3-bromopentane reacts with two moles of OH- in this reaction

f) This is an addition reaction

2007-04-25 10:52:23 · 3 answers · asked by ashleyjohn18 1

Under standard conditions, the volume of air in liters required for complete combustion of 228 grams of octane is about?

A. 22.4
B. 2.50
C. 560
D. 1560
E. 2800

And why please because I don't understand how to solve this.

2007-04-25 10:51:54 · 3 answers · asked by Clarence Thomas 1