Chemistry - October 2007

1) A 2.05 g sample of a metal alloy is heated to 98.88°C. It is then dropped into 28.0 g water in a calorimeter. The water temperature rises from 19.73°C to 22.00°C. Calculate the specific heat of the alloy.

2) A piece of stainless steel (specific heat = 0.50 J/g°C) is taken from an oven at 168°C and immersed in 215 mL of water at 25.9°C. The water temperature rises to 42.4°C. What is the mass of the piece of steel?

2007-10-14 13:01:52 · 1 answers · asked by unknownanonymous999 2

2007-10-14 12:31:06 · 1 answers · asked by ~USA~ 2

In the titration of a weak acid HA with 0.100 M NaOH, the stoichiometric point is known to occur at a pH value of approximately 11. Which of the following indicators would be best to use to mark the endpoint of this titration?

A. an indicator with Ka = 10^-6
B. an indicator with Ka = 10^-8
C. an indicator with Ka = 10^-14
D. an indicator with Ka = 10^-12

2007-10-14 11:44:09 · 1 answers · asked by Anonymous

THE QUESTION:

If the passing of five half-lives leaves 25.0mg of (superscript)90Sr, how much was present in the beginning?


THE EQUATION:
#Left = #Original * (1/2) [exponent]T/h
T= time
H= half life



i don't know how to solve this problem because it doesn't give info for the time OR the half life of Sr...what the heck does 'five half-lives' mean?

please help...thanks

2007-10-14 11:34:49 · 5 answers · asked by Meg 1

What about at what pH will the buffer be half dissociated?

2007-10-14 11:34:45 · 1 answers · asked by Anonymous

2007-10-14 11:32:21 · 2 answers · asked by Anonymous

2007-10-14 11:31:34 · 3 answers · asked by Anonymous

I would like to know if it is relatively safe for me to do so, since it can harm pets, and where could i get melamine.

Please, serious answers only.

2007-10-14 11:24:55 · 2 answers · asked by azn_flute323 1

How come oxygen bubbles form even before water begins to boil?

Thanks

Happy Halloween!

2007-10-14 11:18:52 · 3 answers · asked by UnknownD 6

2007-10-14 11:12:53 · 1 answers · asked by Anonymous

1. A tank contains both Nitrogen and hydrogen gas. If the partial pressure are 190 mmHg and 303 mmHg respectively, what is the mole fraction of nitrogen?

2. if 4.0 grams of hydrogen, 6.02 * 10 ^ 22 atoms of helium and 4.48 L of argon, measures at stp, are placed in a 2.0 Liter flask at 27 degree celcius, what is the final pressure.

2007-10-14 11:11:38 · 1 answers · asked by confused ~ 1

A mixture of oxygen and helium is 92.3% by mass oxygen. It is collected at atmospheric pressure (735 Torr). What is the partial pressure of oxygen in this mixture?

a) 299 Torr
b) 412 Torr
c) 688 Torr
d) 333 Torr
e) 446 Torr

(an explanation would be very helpful, especially what the purpose of the 92.3% would help indicate or just any help at all.)

2007-10-14 11:10:15 · 2 answers · asked by Annie T 1

Calculate the weight of 2.27 moles of Al2O3?

Express your answer in grams of aluminum oxide as three significant digits.

WARNING: Only provide the numerical answer. Do not include the units in the answer box. If you fail to enter your answer in the correct form, it will be counted wrong.

2007-10-14 11:08:41 · 1 answers · asked by Anonymous

Please help me with the following question:) What was the purpose of tube A?
Please help me with the following question:) What was the purpose of tube A?

Procedure:
1. Prepare a stock albumen solution by adding the white of one egg to 100 mL of distilled water in a beaker. Stir until the albumen is in solution.

Place 5 mL of the albumen solution into each of four test tubes. Label the tubes A,B,C,D

Tube A- Let stand at room temperature. Measure the temperature. Determine the pH with pH paper.
Tube B - Heat the tube in a boiling water bath for 10 minutes.
Tube C - Add 2 mL of 1M HCI. Determine the pH of the solution.
Tube D - Add 5 drops of 2% AgNO3 (a salt of the heavy metal silver).

My Observations

Tube Temperature pH appearance
A 21 degrees 7 clear colourless solution
B 100 degrees 7 opaque, white substance
C 21 degrees 2 opaque, white substance
D 21 degrees 7 opaque, white substance

I have been stumped on this question for the last several days
Thanks

2007-10-14 11:08:08 · 2 answers · asked by Mark F 1

Where does nickel fall on the reactivity series of metals?

2007-10-14 11:04:57 · 1 answers · asked by Jada 1

stoichiometry

2007-10-14 11:02:27 · 1 answers · asked by dukebasketball1992 2

How many valence electrons does this ion have ??????????

O2-2

2007-10-14 10:57:14 · 1 answers · asked by Anonymous

ok so combustion of Magnesium and sulfur- how do you do it?

i think:
magnesium:
Mg + O2 ---> MgO2

S + O2 ---> SO2

am i right? if not help me im lost

2007-10-14 10:44:35 · 3 answers · asked by holaaloha12345 4

2007-10-14 10:42:40 · 1 answers · asked by Anonymous

Na3PO4, KI and AlCl3, respectively. These results were found by using a Universal Indicator. I have to write out a net ionic equation to explain my observations for these 3 solutions, but obviously i do not know how to do this.

Please, any help would be greatly appreciated, thanks!!!

2007-10-14 10:32:02 · 1 answers · asked by jellybean0424 2

1. Which type of chemical bond must be present in an electrolyte? How do you know?

2.Distinguish between different types of ions. Give three examples of each type of ion.

3. Why are ionic solids non-conductors of electricity, but good conductors when metal?

4. What should I do when a question askes me to draw a dot diagram, say for phosphine, PH3?

The reason I can't answer these questions is because I don't recall learning about them last year.

2007-10-14 10:25:15 · 1 answers · asked by Memories of Another World. 6

2007-10-14 10:19:35 · 1 answers · asked by mohjd s 1

I need to write out the net ionci equations for Na3PO4, KI, and AlCl3 when mixed with the Universal Indicator. I know how to do net ionic equations, but the problem is, i dont know what the chem. formula for UI is. Oh and I know that Na3PO4 is a base, KI is neutral, and AlCl3 is an acid. Thanks for the help!

2007-10-14 10:07:23 · 1 answers · asked by jellybean0424 2

Balance the equation
? CS2 + ? O2 ! ? CO2 + ? SO2
What are the coefficients?

2007-10-14 09:53:10 · 3 answers · asked by eileen r 1

When Hydrogen gas is passed over heated Lead (IV) Oxide , Silvery beads of Lead are produced. The only other product of the reaction is water in the form of steam.

When the experiment was repeated using Magnesium Oxide instead of Lead (IV) Oxide, no metal was obtained. Explain this result ?


Thanks :D:D:D

2007-10-14 09:43:03 · 1 answers · asked by Anonymous

One of the steps in the manufacture of nitric acid is the combustion of ammonia with oxygen to produce nitrogen dioxide:
NH3+O2→NO2+H2O
How much nitrogen dioxide (in kg) could be produced from 20,000kg of ammonia if the reaction occured in only 72% yield?


Im stuck on this can anyone help me please :)
Thanks soooooo much!

2007-10-14 09:29:32 · 3 answers · asked by Anonymous

2007-10-14 09:29:12 · 2 answers · asked by Anonymous

1) what is the pH of a solution for which [H+] = 2.4 X 10^-7? is this solution acidic or basic?

2) what is the pOH of the same solution?

3) what is the pH of a 3.0 X 10^-4 solution of NaOH? is this solution acidic or basic?

4) what is the molarity of a 2548 L solution that contains 1.37 g HNO3

5) what is the pH, pOH, [OH-] and [H+] for the last problem?

2007-10-14 09:19:43 · 1 answers · asked by Anonymous

Is it impossible to convert ml into grams because grams is a unit for weight and ml is a unit for volume?

For example; for Glucose i only know the molecular weight which is 180 g/mol-1 and the volume of solution in which the glucose is in 20ml. I also know in this 20ml solution there is 2.0% of glucose present.

Can i use this information to calculate the weight in grams of glucose or is that impossible??

2007-10-14 09:16:56 · 5 answers · asked by Varisha 6

I need a balanced symbol equation for :
Magnesium + hydrochloric acid = magnesium chloride + salt + hydrogen.
I think that's right anyway...If there's any problems please say (:
Kthnx.

2007-10-14 09:11:59 · 1 answers · asked by <3 3