Chemistry - April 2007

Talking about buffer systems

2007-04-26 14:49:21 · 1 answers · asked by firebabe_bri 1

For 1.2 mole of the radioactive isotope iron-59, half-life = 45.1 days, how many disintegrations have occurred after 15 minutes?


Thank you sooo much!!

2007-04-26 14:48:18 · 2 answers · asked by Anonymous

2007-04-26 14:46:47 · 1 answers · asked by firebabe_bri 1

2007-04-26 14:44:30 · 1 answers · asked by firebabe_bri 1

How will the height of the liquid column in the student's barometer with a density of 5.5 g/ml. compare to the height of the liquid column in a mercury (density = 13.6 g/ml) barometer?


A. The mercury column will be lower.
B. The mercury column will be higher.
C. The columns will be the same height.
D. More information is needed to answer this question.

2007-04-26 14:43:53 · 1 answers · asked by meee! 1

if the absorbance line goes up aat a particular color region of the spectrum, what does that mean in terms of how the material will look? (color is will be)
what is the relationship between pH and the concentration of a colored ion in solution?

2007-04-26 14:25:40 · 1 answers · asked by Anonymous

Molecular forces to choose from: London forces or Dipole-dipole force or hydrogen bonding forces

a. graphite
b. CH4
c. NH3
d. Cu

2007-04-26 14:04:45 · 1 answers · asked by granny 1

4) Which transformation could take place at the anode of an electrochemical cell?
A) NO → NO3-
B) CO2 → C2O42-
C) VO2+ → VO2+
D) H2AsO4 → H3AsO3
E) O2 → H2O2

2007-04-26 13:57:08 · 1 answers · asked by angeleyez000000 2

For 1.4 mole of the radioactive isotope xenon-133, half-life = 5.3 days, how many disintegrations have occurred after 20 minutes?

Hint:
Think about what disintegrates - a single isotope.
How many isotopes are there in the amount of moles given ?
How many disintegrated is the difference between initial and final number of isotopes


I know one would use the following formula/procedure:
[A]t = [A]0*e^(ln2*t/t 12) to find [A]t.

Then,

[A]0 - [A]t = x.

Finally,

x * 6.022e23.


Though, I can't seem to figure out the correct answer.

Last Answer: 1.53137e31
Incorrect, tries 2/12.

any *help* would be deeply appreciated.

2007-04-26 13:52:03 · 1 answers · asked by L 2

A chemist has a solution that is 60% saline and another solution that is 35% saline. How many ounces of each solution will she need to make 100 ounces of a mixture that is 40% saline?

Please help.

2007-04-26 13:01:53 · 1 answers · asked by Ana Singer 2

I've been getting in trouble for not doing my homework but my teacher doesn't explain anything and I can't figure out how to do these problems, can someone please help me??


1)balanced reaction: 2Ca+O2(2 is a subscript)=2CaO
You wish to calculate the mass of calcium oxide that can be prepared from 4.20g Ca and 2.80g of O2
a)how many moles of CaO can be produced from the given mass of Ca?
b)How many moles of CaO can be profuced from the given mass of O2
c)What is the limiting reactant?
d)How many grams of CaO can be produced?


2)Calculate the maximum numbers of moles and grams of iodic acid [HIO3(3 is a subscript)] that can form when 685g of iodine trichloride reacts with 131g of water:


reaction: ICl3(subscript)+H2O=Icl+HIO3(subscript)+HCl [unbalanced]


What mass of the excess reactant remains?


PLEASE PLEASE PLEASE HELP! I'm at my wits end, I'm usually an A student and I just got a 49 on my last test!! *drops dead*

2007-04-26 13:01:36 · 1 answers · asked by Ashboo 2

The initial temperture of a metal is 369d degrees C and has a mass of 152 pounds. YOu have 88.2 ml of water with an initial temperture os 20.4 degrees C and a final temp of 307K. What is the specific heat of the metal in kcal/mol* K?

2007-04-26 12:52:24 · 1 answers · asked by allyy 2

10. Phosphorus trichloride (PCl3) reacts with hydrochloric acid to produce chlorine gas and phosphine
(PH3):
PCl3 (g) + 3 HCl (g) ? 3 Cl2(g) + PH3 (g) DHrxn = +570.4 kJ
The enthalpies of formation of some compounds are listed in the table below.
Substance DHf (kJ/mol) Substance DHf (kJ/mol)
PCl3 (g) -288.1 H2O, liquid -285.8
HCl (g) -92.3 H2O, gas -241.8
Based on the data provided the enthalpy of formation of gaseous phosphine, PH3 (g), is _____.

The answer is 5.4 Kilojoules per mole but how do you figure it out??

2007-04-26 12:47:29 · 1 answers · asked by iammindfreak 3

I need help for this lab I recently did. I'm supposed to find the theoretical value (Volume of H2 produced) which was 49.32 mL at STP using stoichiometry...how do I do that?

(Mg + 2HCl ---> MgCl2 + H2)

2007-04-26 12:42:37 · 1 answers · asked by Anonymous

A titration was done, 50mL of 0.1 mol/L NaOH added into 25mL of CH3COOH (initial pH = 3.5)

this is what i've worked out so far:
chem equation: CH3COOH(aq) + NaOH(aq) <--> NaCH3COO(aq) + H2O(l)

dissociation of CH3COOH = CH3COOH(aq) + H2O(l) <--> CH3COOˉ(aq) + H3O + (l)

inital pH of CH3COOH(aq) = 3.5
initial [CH3COOH(aq)] = 0.2 mol/L (n = 5mmol, V = 25mL)
inital [NaOH] = 0.1mol/L (n = 5mmol, V = 50mL)

this is what i'm asked to do:

Use the initial pH of the CH3COOH (before you added any based (3.5)) to find the initial [H3O]. What was the initial [CH3COO-]

Assume the amount of CH3COOH that dissociates is small compared with the initial concentration of the acid. If this is true, the equilibrium valye of [CH3COOH] is equal to the initial concentration of the acid. Use your valuse of [H3O+],[CH3COO-] and [CH3COOH] to calculate Ka for acetic acid.

i worked it out to be 5 x 10^-7, but i'm pretty sure that is wrong.

2007-04-26 12:31:21 · 1 answers · asked by Anonymous

How exactly could i get mentos into a container of coke with the head of the coke pointing down.. and how would i get it to blow... and how would i get it in from the bottom????

2007-04-26 11:20:00 · 1 answers · asked by Anonymous

2007-04-26 11:12:30 · 1 answers · asked by uchers 1

Please provide calculations. Thanks! :-)

2007-04-26 10:52:25 · 1 answers · asked by Anonymous

Which of the following statements are true?

SiCl4(l) + 2Mg(s) --> 2MgCl2(s) + Si(s)


a) Mg is the reducing agent



b) SiCl4 is the reducing agent



c) Mg is oxidized


d) SiCl4 (or Si in SiCl4) is oxidized



e) CH4(g) + 2O2(g) --> CO2(g) + 2H2O(g) is a redox reaction



f) O3(g)(aq) + NO(g) --> O2(g) + NO2(g) is a redox reaction

2007-04-26 10:10:25 · 1 answers · asked by Craig M 1

A. If the benzophenone used to prepare triphenylmethanol was wet, what organic by-product would form?
B. How do you write a stepwise mechanism for triphenylmethanol (diethylcarbonate w/ phenylmagnesium bromide)?

2007-04-26 10:07:16 · 2 answers · asked by Karma 2

2007-04-26 10:01:12 · 2 answers · asked by fallbaby80 1

eg, 1,1,1 trichloroethylene or n,l,lysergic acid diethylamide

2007-04-26 09:53:33 · 5 answers · asked by Anonymous

The combustion of gasoline releases tremendous amounts of heat. It is the work done on the piston that is the main goal of the reaction, so systems are developed to remove the excess heat produced, since only about 30% of the energy from gasoline is used as work.

2 C8H18 (l) + 25 O2 (g) → 16 CO2 (g) + 18 H2O (g) H = –10110 kJ

C)Let's say that the temperature at which your engine parts begin to melt is 3500 °C. Can your engine handle the temperature you calculated in part b.? Explain your answer.

D)Your engine has an elaborate cooling system that allows it to maintain a reasonable temperature by transferring heat to a coolant. One coolant option may be water. Knowing that water has a high specific heat, freezes at 0 °C, and boils at 100 °C, discuss the pros and cons of using water as your coolant.

2007-04-26 09:36:48 · 2 answers · asked by SUKE! 1

My chemistry teacher never explained rules for net ionic equations and when i read the text i understood the rules, except in this particular instance as it wasn't specified. write the net ionic equation of the following reaction:
Ca(s) + 2HCl(aq) yields CaCl2(aq) + H2(g)

2007-04-26 09:23:28 · 3 answers · asked by transfering student 1

1. Consider the following substances and determine the strongest type of intermolecular force for each. Explain your reasoning.

A beaker of CH3OH (l)

A beaker of BF3 (l)

A beaker of NH3 (l)

A solution of CH3Cl (aq) and Ca2+ (aq)

A flask of CO2 gas

A solution of HBr (aq)

paraffin (large nonpolar molecule)



2. Explain why candle wax (paraffin) is a solid at room temperature, vegetable oil (medium sized molecule) is a liquid, and carbon dioxide is a gas.

2007-04-26 09:07:04 · 2 answers · asked by sukeschool 1

Which experiement led to the belief that atoms consist of a dense positively charged center (ie; the nucleus) which is separated from the negatively charged electrons by empty space?

2007-04-26 09:06:58 · 1 answers · asked by perko23 2

Which of the following mixtures would result in buffered solutions when 1.0L of each of the two solutions are mixed?

0.1M KOH and 0.1M CH3NH3Cl
and
0.1M KOH and 0.2M CH3NH2

how do you figure it out???

2007-04-26 09:06:39 · 1 answers · asked by Nicole S 1

Carbon-12 has 6 protons and 6 nuetrons. Carbon-13 has 6 protons and 7 nuetrons. Whare are these two atoms called?

2007-04-26 09:00:39 · 12 answers · asked by perko23 2

2007-04-26 08:59:20 · 1 answers · asked by Patricia G 1

Some someone please explain how to do this problem and the answer to it. It would be greatly appreicated.

Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g)

What is the volume, in liters, of H2 gas produced at 24°C and 835 mm Hg, from the reaction of 13.4 g Mg?

2007-04-26 08:54:39 · 3 answers · asked by Anonymous