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MID TEST (UTS) Basic Chemistry I

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MID TEST (UTS) Basic Chemistry I

November 14, 2012 0 Comments A+ a-

MID SEMESTER TEST
COURSE : BASIC CHEMISTRY I
NAME : RINALDI PRASETIA
NIM : RSA1C112011




  1.   Question :
    1.   pure substance X is solid at room temperature. if the substance is heated to 2300C is melted gradually. if then cooled to room temperature, the liquid can not be frozen
    a.        is it possible X of an element or a compound. explain it!

    answer :
    I think X is a compound substance because the substance X there is a temperature or temperature where it shows the boiling point and melting point where the reaction can be smelted though gradually. And also substance X indicates the compound is ionic compound shown by the boiling point and high melting.

    b.      does it a chemical change occured? if so can it be said to undergo an endoterm changing, based on the information provided?

    answer :
    Substance X can be regarded as a change when heated at a temperature of 2300C occurred a little fusion, albeit slightly. Consolidation is changing the substance X from solid to liquid.

    c.       Can it be said that the liquid is an element, based on the information provided

    answer :
    I think that could be because the elements are part of the underlying basis of something where, the fluid element is an element that is composed of elements / structure of an element that is liquid or liquid. such as hydrogen and oxides that react to H2O.  

       Question :
    2.       When a candle that weight 10 gr is burned in oxygen, carbon dioxide and water vapor formed by combustion the weight more than 10 gr. Was this case match with the law of mass. Explain it.

    answer :
    It is not contrary to the law of conservation of mass, due to the law of conservation of mass is explained that the mass of a substance before and after the same or unchanged. And also in the reaction above Hannya weight change and explained that there was no mass change. So it belongs to the law of conservation of mass.

      Question :
    3.       When carbon burns in oxygen under limited number, it will form two gaseous compounds. Suggest the way to differentiate the two compounds with one another.

    answer :
    In my opinion, to differentiate the two compounds formed from carbon gas that burns oxygen. To do the experiment qualitatively to distinguish or know the chemical to know the difference.

      Question :
    4.       After mendeev compiled theperiodic table, he conclude that the atomic weight of certain elements was wrong ruling, and this conclusion was apparently correct. How Mendeleev was able to predict that several atomic weight were wrong? Why his predictions are not always right. Explain!

    answer :
    Predictions are not always correct because the periodic Mendelev, long periods in the periodic system are not the same and why not described. That is what makes his predictions are not always right.

      Question :
    5.       When an aqueous mercury chloride solution is added to an aqueous solution of silver nitrate, a white solid forms. Identify the white solid and write the balanced equation for the reaction that occurs.

    answer :
    HgCl2 + 2AgNO3 à Hg (NO3)2 + 2AgCl



Electronegativity of The Periodic Trends

November 06, 2012 4 Comments A+ a-

Electronegativity is a measure of the ability of an atom or molecule to attract electron pairs in the context of chemical bonds.Electronegativity can not be calculated directly, but must be calculated from the properties of atoms and molecules. Several methods of calculation have been proposed. Although in every method there is little difference in the numerical value of the electronegativity, all methods have the same trend in the period between the elements.
 The most commonly used method is the method of Pauling. The results of this calculation produces a dimensionless value and is usually referred to as the Pauling scale relative scale that ranged from 0.7 to 4.0 (hydrogen = 2.2). When other methods of calculation is used, there is a convention (although not required) to use the same scale range Pauling scale: this is known as an electronegativity in Pauling units.
Electronegativity is not part of the nature of the atom, but only the nature of atoms in molecules. Properties of single atoms is equal to the electron affinity electronegativity. Electronegativity in an element will vary depending on the chemical environment, but it is usually regarded as a property of displaced, an electronegativity value is considered to apply to various situations vary.
Carbon-fluorine bond
Fluorine is much more electronegative than carbon. Original value Pauling scale is
 carbon
2.5
fluorine
4.0
This means that the fluorine attract electrons more strongly than carbon. Ties on average will look like this:

http://www.chem-is-try.org/wp-content/migrated_images/belajar_korganik01_07/image002.gif

Carbon-chlorine bond
Its electronegativity is:
 carbon
2.5
 chlorine
3.0

Pair bonding electrons will be drawn to chlorine but not as strong as in florins. Because chlorine is not senegatif florins.




  Bond polarity and inductive effects
Polarity bond
Think about the carbon-fluorine bond again. Because the bonding pair of electrons pulled towards the side of the florin would be more negative. While the pair of carbon becomes slightly more electron deficiency and be more positive.
 http://www.chem-is-try.org/wp-content/migrated_images/belajar_korganik01_07/image004.gif
symbols + and - means "more positive" and "more negative". + Read with the "delta plus" or "positive delta".
We describe a bond that has the more negative and more positive as polar.
  Inductive effect
A fluorine atom as to attract the electron pair bond is said to have a negative inductive effect.
Most of the atoms that you would have encountered mostly have negative inductive effect when bonded to carbon because they are more electronegative than carbon.
 You will also find some group of atoms that has little inductive effect posotif. They push the electrons to the carbon they are bonded and makes it more negative.
Inductive effects are often given the symbol: I-(negative inductive effect) and + I (positive inductive effect).
  Some important examples of polar bonds
Hydrogen Bromide (and other hydrogen halides)
 http://www.chem-is-try.org/wp-content/migrated_images/belajar_korganik01_07/image006.gif
Bromine (halogen and others) are all more electronegative than hydrogen halide and all hydrogen bonds have polar bonds with the hydrogen halides are more positive and more negative parts.
The polarity of these molecules is crucial as they react with alkenes.
Carbon-bromine bond in Halogenoalkena
Bromine is more electronegative than carbon that bonds polarized as we have language support in CF and C-l.

The polarity of the carbon-halogen important in halogenoalkanes reaction.

Carbon-oxygen bond
A model orbital of the C = O at methanal, CHCHO, looks like this:
 http://www.chem-is-try.org/wp-content/migrated_images/belajar_korganik01_07/image008.gif
The most electronegative oxygen atoms attract both spouses ties to him. And it resulted in more negative oxyg
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