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fandomhigh2006-02-15 11:12 am
equalsmcsquared.livejournal.com) wrote in fandomhigh2006-02-15 11:12 am
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There is a new classmate this morning in the form of a hyperactive puppy. Said puppy is laying on Ms. Sidle's lap.
"Classification is fundamental in biology. Systems of classification are conceptual structures that reflect interpretation of available data regarding evolutionary relationships. Interpretations differ and new information is constantly emerging from many sources. Thus, flowering plant classification reflects an on-going scientific activity - there is no single, stable classification."
She lectures extensively on plant taxonomy history.
"Please turn in the homework I assigned on Monday.
While the empirical formula is the simplest form of a compound, the molecular formula is the form of the term as it would appear in a chemical equation. The empirical formula and the molecular formula can be the same, or the molecular formula can be any positive integer multiple of the empirical formula. Examples of empirical formulas: AgBr, Na2S, C6H10O5. Examples of molecular formulas: P2, C2O4, C6H14S2, H2, C3H9.
One can calculate the empirical formula from the masses or percentage composition of any compound. We have already discussed percent composition in the section above. If we only have mass, all we are doing is essentially eliminating the step of converting from percentage to mass.
Example: Calculate the empirical formula for a compound that has 43.7 g P (phosphorus) and 56.3 grams of oxygen. First we convert to moles:
Next we divide the moles to try to get a even ratio.
When we divide, we did not get whole numbers so we must multiply by two (2). The answer=P2O5
Calculating the molecular formula once we have the empirical formula is easy. If we know the empirical formula of a compound, all we need to do is divide the molecular mass of the compound by the mass of the empirical formula. It is also possible to do this with one of the elements in the formula; simply divide the mass of that element in one mole of compound by the mass of that element in the empirical formula. The result should always be a natural number.
Example: if we know that the empirical formula of a compound is HCN and we are told that a 2.016 grams of hydrogen are necesary to make the compound, what is the molecular formula? In the empirical formula hydrogen weighs 1.008 grams. Dividing 2.016 by 1.008 we see that the amount of hydrogen needed is twice as much. Therefore the empirical formula needs to be increased by a factor of two (2). The answer is:
H2C2N2.
"There will be a text next Monday. Study."
Investigators can prove that a fire was set intentionally by finding an accelerant at the scene of a fire. An accelerant is a chemical fuel that causes a fire to burn hotter, spread more quickly than usual, or be unusually difficult to extinguish. The presence of an accelerant in fire debris can be used as evidence of arson.
The most commonly used accelerants are gasoline, kerosene, turpentine, and diesel fuel. These are all organic compounds containing mixtures of hydrocarbon molecules. As accelerants evaporate, the hydrocarbons more into the air above the fire debris, which is called the "headspace."
Various techniques exist to detect accelerants at a fire scene. These range from an experienced fire investigator or a specially trained "sniffer" dog using their sense of smell to detect the characteristic odor of various accelerants in the surrounding air, to more complex laboratory methods.
One of the most advanced techniques for detecting accelerants in fire debris is called headspace gas chromatography. Gas chromatography involves separating mixtures of gases into their individual components based on the different boiling points of their hydrocarbons. Each gas in the mixture can then be identified, because each produces a distinct chemical fingerprint called a chromatogram.
In headspace gas chromatography, solid debris taken from the suspected point of origin of the fire is placed in an airtight vial to prevent any accelerants from evaporating. The vial is then heated, releasing the accelerant's hydrocarbons into the trapped headspace above the debris. A needle is inserted through the cap of the vial to remove a sample of the hydrocarbons and inject them into an instrument called a gas chromatogram for separation and analysis.
If an accelerant is used to start a fire, a small amount will likely still be present in the charred debris. Identification of the accelerant can serve as physical evidence to support a charge of arson.
"Classification is fundamental in biology. Systems of classification are conceptual structures that reflect interpretation of available data regarding evolutionary relationships. Interpretations differ and new information is constantly emerging from many sources. Thus, flowering plant classification reflects an on-going scientific activity - there is no single, stable classification."
She lectures extensively on plant taxonomy history.
"Please turn in the homework I assigned on Monday.
While the empirical formula is the simplest form of a compound, the molecular formula is the form of the term as it would appear in a chemical equation. The empirical formula and the molecular formula can be the same, or the molecular formula can be any positive integer multiple of the empirical formula. Examples of empirical formulas: AgBr, Na2S, C6H10O5. Examples of molecular formulas: P2, C2O4, C6H14S2, H2, C3H9.
One can calculate the empirical formula from the masses or percentage composition of any compound. We have already discussed percent composition in the section above. If we only have mass, all we are doing is essentially eliminating the step of converting from percentage to mass.
Example: Calculate the empirical formula for a compound that has 43.7 g P (phosphorus) and 56.3 grams of oxygen. First we convert to moles:
Next we divide the moles to try to get a even ratio.
When we divide, we did not get whole numbers so we must multiply by two (2). The answer=P2O5
Calculating the molecular formula once we have the empirical formula is easy. If we know the empirical formula of a compound, all we need to do is divide the molecular mass of the compound by the mass of the empirical formula. It is also possible to do this with one of the elements in the formula; simply divide the mass of that element in one mole of compound by the mass of that element in the empirical formula. The result should always be a natural number.
Example: if we know that the empirical formula of a compound is HCN and we are told that a 2.016 grams of hydrogen are necesary to make the compound, what is the molecular formula? In the empirical formula hydrogen weighs 1.008 grams. Dividing 2.016 by 1.008 we see that the amount of hydrogen needed is twice as much. Therefore the empirical formula needs to be increased by a factor of two (2). The answer is:
H2C2N2.
"There will be a text next Monday. Study."
Investigators can prove that a fire was set intentionally by finding an accelerant at the scene of a fire. An accelerant is a chemical fuel that causes a fire to burn hotter, spread more quickly than usual, or be unusually difficult to extinguish. The presence of an accelerant in fire debris can be used as evidence of arson.
The most commonly used accelerants are gasoline, kerosene, turpentine, and diesel fuel. These are all organic compounds containing mixtures of hydrocarbon molecules. As accelerants evaporate, the hydrocarbons more into the air above the fire debris, which is called the "headspace."
Various techniques exist to detect accelerants at a fire scene. These range from an experienced fire investigator or a specially trained "sniffer" dog using their sense of smell to detect the characteristic odor of various accelerants in the surrounding air, to more complex laboratory methods.
One of the most advanced techniques for detecting accelerants in fire debris is called headspace gas chromatography. Gas chromatography involves separating mixtures of gases into their individual components based on the different boiling points of their hydrocarbons. Each gas in the mixture can then be identified, because each produces a distinct chemical fingerprint called a chromatogram.
In headspace gas chromatography, solid debris taken from the suspected point of origin of the fire is placed in an airtight vial to prevent any accelerants from evaporating. The vial is then heated, releasing the accelerant's hydrocarbons into the trapped headspace above the debris. A needle is inserted through the cap of the vial to remove a sample of the hydrocarbons and inject them into an instrument called a gas chromatogram for separation and analysis.
If an accelerant is used to start a fire, a small amount will likely still be present in the charred debris. Identification of the accelerant can serve as physical evidence to support a charge of arson.