3/20/11
Dilution calculation (juice)
Suppose you have 2 L of orange drink containing 50% orange juice and 50% water (by volume). The drink was made from 1 L of orange juice and 1 L of water. You want to dilute this drink so that it contains only 20% orange juice. How much water should you add?
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A 20% orange juice-water mixture would contain 20 parts juice in 100 parts of mixture (by volume).
20/100 = 1/5
The above ratio shows that we would have 1 part juice to 5 parts total. The 2 liters of made up orange drink contains 1 liter of juice and one liter of water. If we added 3 more liters of water, we would have 1 liter juice in 5 liters total.
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Carbon-14 Dating Calculation
A linen scroll contains 80.9% of Carbon-14 that it contain when new. How old are the scrolls if the half-life for deacy is 5.73X10^3?
- - - - - - - - - -
ln(M/Mo) = -kt
n = natural log
M = mass left (not needed)
Mo = original mass (not needed)
(M/Mo) = 0.809
k = 0.693/T(half)
T(half) = 5.73x10^3 years.
- - - - - - - - - -
- - - - - - - - - -
ln(M/Mo) = -kt
n = natural log
M = mass left (not needed)
Mo = original mass (not needed)
(M/Mo) = 0.809
k = 0.693/T(half)
T(half) = 5.73x10^3 years.
- - - - - - - - - -
4/21/08
The Glowing Pickle
Q. If you hook up a pickle to a 110V power supply and then turn the electricity on, the pickle starts to glow with a yellow color. Why might this be happening? HINT: Pickles are made by soaking cucumbers in very concentrated salt solution.
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A. If you dip a clean wire into a clean salt solution and then place it into a flame [with precautions to protect your hand], it glows yellow because of the sodium in the salt. Sodium outdoor lights produce yellow light also by heating sodium vapor to a very high temperature.
The strange thing about the glowing pickle is that it is not very hot. Attempts to explain the yellow glow contain assumptions that have not been proven. Most of them assume that sodium atoms in the salt somehow become activated enough to give off yellow light. That sounds very reasonable and it is probably correct.
The problem is explaining the activation of sodium without raising the average temperature of the pickle very much. The water in the pickle is not even boiling. Yet, sodium atoms become activated enough to produce the yellow-orange glow.
Some Internet sites post explanations that promote the idea of mini electric arcs within the pickle: Multiple electric sparks jumping across little spaces formed by steam inside the pickle. However, no serious, systematic experimental study has been undertaken to solve the glowing pickle mystery. Take a look at the web pages below and the links in those pages:
http://www.exo.net/~pauld/activities/aaptelectric/glowingpickle.html
http://www.winzy.com/word/Pickle%20Light%20Experimen
http://home.nycap.rr.com/useless/pickle/index.htm
----------------------------
A. If you dip a clean wire into a clean salt solution and then place it into a flame [with precautions to protect your hand], it glows yellow because of the sodium in the salt. Sodium outdoor lights produce yellow light also by heating sodium vapor to a very high temperature.
The strange thing about the glowing pickle is that it is not very hot. Attempts to explain the yellow glow contain assumptions that have not been proven. Most of them assume that sodium atoms in the salt somehow become activated enough to give off yellow light. That sounds very reasonable and it is probably correct.
The problem is explaining the activation of sodium without raising the average temperature of the pickle very much. The water in the pickle is not even boiling. Yet, sodium atoms become activated enough to produce the yellow-orange glow.
Some Internet sites post explanations that promote the idea of mini electric arcs within the pickle: Multiple electric sparks jumping across little spaces formed by steam inside the pickle. However, no serious, systematic experimental study has been undertaken to solve the glowing pickle mystery. Take a look at the web pages below and the links in those pages:
http://www.exo.net/~pauld/activities/aaptelectric/glowingpickle.html
http://www.winzy.com/word/Pickle%20Light%20Experimen
http://home.nycap.rr.com/useless/pickle/index.htm
3/2/08
Unit Cell Volume
The smallest repeating unit of s crystal of table salt(the unit cell) is a cube with an edge of .0563nm. If the density of NaCl is 2.17 g/cm^3, what is the mass in grams of one unit cell?
==========================
The edge of a unit cell in meters is:
1 nm = 1.00x10^-9m
Since 1 m = 100 cm = 10^2 cm,
(1.00x10^-9m)(10^2cm/m) = 1.000x10^-7 cm
The volume of a unit cell is:
(1.00x10^-7cm)^3 = 1.00x10^-21 cm^3
mass(unit cell) = (2.17 g/cm^3)(1.00x10^-21 cm^3) = 2.17x10^-21 g
==========================
The edge of a unit cell in meters is:
1 nm = 1.00x10^-9m
Since 1 m = 100 cm = 10^2 cm,
(1.00x10^-9m)(10^2cm/m) = 1.000x10^-7 cm
The volume of a unit cell is:
(1.00x10^-7cm)^3 = 1.00x10^-21 cm^3
mass(unit cell) = (2.17 g/cm^3)(1.00x10^-21 cm^3) = 2.17x10^-21 g
Saline Solution
On 2/4/08 2:30 PM, "emaildave" wrote:
Physiological saline is a .9% solution of NaCl. (a) Express this in terms of molar or millimolar concentrations. (b) Make 125 mL of physiological saline.
=======================
(a) 0.9% means 0.90g NaCl / 100 mLs
The above concentration is equivalent to 9.0g / 1000mLs or 9.0g / liter
The molar mass of NaCl is 23.0 + 35.45 = 58.45 g/mole of NaCl
(9.0g/L) / (58.45 g/mol) = 0.154 moles NaCl / liter or 154 millimoles/liter
NOTE:
1 Mole of NaCl contains 2 moles of ions (Na+ and Cl-). The above molar concentration is equivalent to:
(0.154 mol/L)(2 moles of ions/mol) = 0.308 moles of ions / liter.
This adjusted molarity is called “osmolarity”. “Colligative” properties such as osmotic pressure, freezing point depression, boiling point elevation, vapor pressure, etc. depend on osmolarity rather than molarity.
(b) (0.125L)(0.154mol/L)((58.45 g/mol) = 1.125g/L NaCl
Physiological saline is a .9% solution of NaCl. (a) Express this in terms of molar or millimolar concentrations. (b) Make 125 mL of physiological saline.
=======================
(a) 0.9% means 0.90g NaCl / 100 mLs
The above concentration is equivalent to 9.0g / 1000mLs or 9.0g / liter
The molar mass of NaCl is 23.0 + 35.45 = 58.45 g/mole of NaCl
(9.0g/L) / (58.45 g/mol) = 0.154 moles NaCl / liter or 154 millimoles/liter
NOTE:
1 Mole of NaCl contains 2 moles of ions (Na+ and Cl-). The above molar concentration is equivalent to:
(0.154 mol/L)(2 moles of ions/mol) = 0.308 moles of ions / liter.
This adjusted molarity is called “osmolarity”. “Colligative” properties such as osmotic pressure, freezing point depression, boiling point elevation, vapor pressure, etc. depend on osmolarity rather than molarity.
(b) (0.125L)(0.154mol/L)((58.45 g/mol) = 1.125g/L NaCl
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