MID TEST
Lecturer : Drs. Syamsurizal, M.Ed

21 November 2011 

1.   1   Pure subtance X is solid at room temperature. If the subtance is heated to 230 c 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
.a I think X is an element, because according to the explanation about
 X is a pure substance then I can simpulkn senyawa.karena bhwa X is a single compound is a substance formed from multiple elements through chemical reactions and compounds also can be decomposed again into its constituent elements by chemical reactions. For example, dihydrogen monoxide (water, H2O) is a compound consisting of two hydrogen atoms for every oxygen atom

 b.      Does it a chemical chage occured? If so can it be said to undergo an endotherm changing, based on the information provided?

Answer

b.yes,Because change is a process or a chemical reaction can not be That Occurs completely happen, obviously re-forms the endothermic reaction, because there is a decrease in temperature, of the substance with a temperature of 230 dipnaskan pda temperature and then cooled automatic room temperature turun.pada haracteristics of the reaction is endothermic reaction heat and the temperature Decrease require 


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

Answer
c. I think not, because the substance X is heated(burned) with a temperature of 230, X reacts with the substance automatic oksiigen to process produced fluidsheted.it so not can be said of an element as it was reacted with compound is the union oksigen.becouse understanding of some elements.


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

 Answer
. I think not, this includes deviations masa.becouse conservation laws according to the law of conservation of lavosier Antoni is "the substance before and after the reaction is the same". While on a matter that occurred after the addition of the clearreaktion it so this very defiance of the laws of conservation of the .

3.    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. C + O2 CO2  C + 2O2 ⅟ CO
CO, is a colorless gas, odorless, and tasteless. It consists of one carbon atom covalently bonded to one oxygen atom. Carbon monoxide is formed when there is a lack of oxygen in the combustion process.While CO2 or carbonic acid substance is a kind of chemical compound composed of two oxygen atoms covalently bonded to a carbon atom. Carbon dioxide is a gas that is colorless and odorless. When inhaled at concentrations much higher than the concentration of carbon dioxide in the atmosphere,it will taste sour in the mouth and nose and tenggorokan..While CO is harmful when inhaled substance because it is inhaled toxins.

4.     4. After medelev compiled the periodic table, he concluded that the atomic weight of certain elements wass wrong ruling, and this conclusion wass apparently correct. How mendeleev was able to predict that several atomic weights were wrong? Why his predictions are not always right. Explain

 

 

Answer

I think why Mendeleev could know why predictions about the gold atom is wrong ... because he standardized.
 repeatedly tried to arrange them so often upside down, plus the atomic determine procedure has not been why prediction not always true .... because according to sya mendelev human also weakness to own, plus the equipment to do research dizaman was not too full



5.  When an aqueous solution of merkuri chloride 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.

.

AnswerHgCl2 2AgNO3 2AgCl + + Hg (NO3) 2White precipitate was 2AgCl, because if the anion Ag cations reacted with Cl will produce soluble compounds, which form a white precipitate.

CHEMICAL REOCTION

The chemical reaction is a natural process that always results antarubahan chemical compounds. 
[1] The compounds or compounds involved early in the reaction is referred to as reactants. Chemical reactions are usually characterized by a chemical change, and will result in one or more products which typically have characteristics different from the reactants. Classically, chemical reactions involve changes involving the movement of electrons in the formation and breaking of chemical bonds, although the general concept is basically a chemical reaction can also be applied to the transformation of elementary particles such as in nuclear reactions.

Reactions with different chemical used in chemical synthesis to produce the desired compounds. In biochemistry, series of chemical reactions that are catalyzed by enzymes form metabolic trajectory, in which the synthesis and decomposition is usually not possible in the cell do.

GROUPING OF CHEMICAL REACTION


Isomerization, in which chemical compounds undergo structural rearrangement without any change in its atomic kompoasisi
    Direct combination or synthesis, in which two or more elements or compounds unite to form a complex product:

    N2 + 3 H2 → 2 NH3

    Chemical decomposition or analysis, in which a compound is broken down into smaller compounds that:

    2 H2O → 2 H2 + O2

    Single replacement or substitution, characterized by an element is replaced by a more reactive element:

    2 Na (s) + 2 HCl (aq) → 2 NaCl (aq) + H2 (g)

    Metathesis or double replacement reaction, two compounds which change each other ions or bonds to form different compounds:

    NaCl (aq) + AgNO3 (aq) → NaNO3 (aq) + AgCl (s)

    Acid-base reaction, a reaction widely between the acid with a base. It has various definitions depending on the acid-base concept is used. Some of the most common definitions are:
        Arrhenius definition: acids dissociate in water releasing H3O + ions; bases dissociate in water releasing OH-ions.
        Brønsted-Lowry definition: Acids are proton donors (H +) donors; base is the recipient (acceptor) protons. Surrounding the Arrhenius definition.
        Lewis definition: Acids are electron pair acceptors; bases are electron pair donors. This definition encompasses Brønsted-Lowry definition.
    Redox reactions, in which there is a change in oxidation number of atoms of compounds that react. This reaction can be interpreted as electron transfer. Examples of redox reactions are:

    2 S2O32-(aq) + I2 (aq) → S4O62-(aq) + 2 I-(aq)
    Which one is reduced to I-I2 and S2O32-(thiosulfate anion) is oxidized to S4O62-.

    Combustion, is a kind of redox reaction in which the materials can be burned to join the elements of an oxidant, usually oxygen, to generate heat and form oxidized products. The term combustion is usually used to refer only to the oxidation of a large scale in the whole molecule. Controlled oxidation at only one single functional group is not included in the combustion process.

    C10H8 + 12 O2 → 10 CO2 + 4 H2O
    CH2S + 6 F2 → CF4 + 2 HF + SF6

    Disproportionation, with one reactant to form two types of products that differ only in oxidation state.

    2 + → Sn Sn2 + + Sn4

    Organic reactions, encompassing various types of reactions involving compounds which have carbon as its main element.


 CHEMICAL KINETICS 

Reaction rate of a chemical reaction is a measurement of how the concentration or pressure of the substances involved in reactions change over time. Analysis of the reaction rate is very important and has many uses, for example in chemical engineering and chemical equilibrium studies. The rate of reaction is fundamentally dependent on:

    The concentration of reactants, which usually make the reaction go faster if the concentration is increased. This is caused due to an increase pertumbukan atoms per unit time,
    Surface area available for the reactants to interact, especially solid reactants in heterogeneous systems. Large surface area will increase the reaction rate.
    Pressure, with increasing pressure, we lowered the volume between molecules so that it will increase the frequency of molecular collisions.
    Activation energy, which is defined as the amount of energy needed to create a reaction that everything starts and goes spontaneously. Higher activation energies imply that the reactants need more energy to start the reaction than the reaction activation energy is lower.
    Temperature, which increases the reaction rate when raised, this is because high temperatures increase the energy of the molecule, thereby increasing inter-molecular collisions per unit time.
    The presence or absence of catalysts. Catalysts are substances that change the trajectory (mechanism) of a reaction and will increase the reaction rate by lowering the activation energy necessary for the reaction can be run. Catalysts are not consumed or changed during the reaction, so that it can be reused.
    For some reactions, the existence of electromagnetic radiation, especially ultraviolet, is needed to decide the bond required for the reaction can be everything starts. This mainly occurs in reactions involving radicals.
The rate of reaction is related to the concentration of substances involved in the reaction. This relationship is determined by the rate equation for each reaction. It should be noted that some reactions have a pace that does not depend on the concentration of the reaction. This is referred to as zero-order reaction.

The development of understanding of atomic structure in line with modern chemical science awalperkembangan. The first scientist to membangunmodel (structure) atom is John Dalton, and then gradually by JJ disempurnakansecara Thomson, Rutherford, and Niels Bohr. 

1. Atomic Model DaltonDalton's atomic theory is based on quantitative measurements of chemical reactions. Dalton produces some of the following postulates.

    Material composed of particles of very dense and small that can not be broken again. The particles were called atoms.
    The atoms of an element are identical in all respects, but different from atoms of other elements.
    In chemical reactions, occurring merger or separation and rearrangement of the atoms from one composition to another composition.
    Atoms can combine with other atoms to form a molecule with a simple comparison.
The conclusion of Dalton atomic model, which consists of elements of the same atoms in all things, good shape, size, and mass, but different from atoms of other elements. In other words, the atom is the smallest particle of an element that still has the properties of that element.
Dalton's Atomic Theory 

2. Thomson Atomic ModelBased on the fact that electrons are fundamental particles making up matter, prompting Thomson to build an atomic modelto refine the atomic theory of Dalton because Dalton's atomic model does not indicate the presence of electrical properties. According to Thomson, atoms contain negatively charged electrons and the electrons are spread evenly throughout the atom. Atom itself is assumed to be a solid ball is positively charged. If Thomson's atomic model is described in three dimensionswould like a cake balls, sesame ore onde declared states of electrons and form atoms. Figure 1.11 shows the atomic modelThomson. If Thomson's atomic model halved then the electrons in the atom would look like pink stone ore spread evenly in the guava.Thomson Atomic Model
3. Rutherford Atom ModelRutherford's experiment shooting a very thin plate of gold with alpha particles emitted by radioactive elements. Data from the experiments showed that the majority of alpha particles can pass through the plates of gold, but only a small fraction of alpha particles are reflected back. Figure 1.12 shows a diagram of alpha particle scattering.Rutherford Experiment
Based on that data, Rutherford concluded that the volume of the atom mostly empty space. This is shown by the number of alpha particles that can pass through the gold plate. Presence of alpha particles that are reflected due to collide with a particle that is very hard with very small size. Rutherford named it as the core of an atomic particle. Therefore, the positively charged alpha particles it must be positively charged nucleus. If the negatively charged atomic nucleus there will be a tug between atomic nuclei and alpha particles.Based on these experiments, Rutherford devised a model of the atom (see Figure 1.13) to refine the atomic models of Thomson. The model developed by Rutherford is as follows.1. Atomic nuclei are composed of positively charged and electrons negatively charged.2. Most of the volume of an atom is empty space whose mass is concentrated in the nucleus.3. Hence the number of neutral atoms positive charge must equal the number of negative charge.4. Inside the atom, the negatively charged electrons are always moving around the atomic nucleus.Rutherford Atom Model
Weaknesses Rutherford Atomic ModelLike its predecessor the atomic model, Rutherford's atomic theory has flaws. The main drawback lies in the movement of electrons around the nucleus in an atom.According to the Law of Classical Physics of Maxwell, if an electrically charged particle moving in a circle will emit energy in the form of light which resulted in the acceleration of particles decreases and finally silent. Thus, if the negatively charged electrons moving in a circle (around the positively charged nucleus) then it will lose its energy so that the movement of electrons is reduced, which will eventually fall into the nucleus. Figure 1.14 shows the Rutherford atomic model according to Maxwell's theory.So, according to the Law of Classical Physics, Rutherford atomic model is not stable because the electron will lose energy and fall into the nucleus, the atom will eventually perish. However, the fact that the atom is stable. 

4. Bohr Atom ModelIn 1913, Danish physicist, Niels Bohr states that the failure of the Rutherford atomic model can be enhanced byapply the Quantum Theory of Planck. Bohr's atomic model is expressed in the form of four postulates relating to the movement of electrons, which are as follows.

    In the surrounding atomic nuclei, electrons are on the (track) specific. This skin is a stationary motion (settling) of the electrons in the atomic nucleus surrounded by a certain distance.
    During the electron is at a certain stationary trajectory, fixed electron energy so that no energy is emitted or absorbed.
    Electrons can switch from one skin to another skin. In this transition, which involved the same amount of energy with Planck equation, ΔE = h.
    Stationary trajectory of the electrons have angular momentum. The amount of angular momentum is a multiple of nh/2π, where n is the quantum number and h is Planck's constant.
Bohr Atom Model
Trajectory of the electrons in the skin or around the nucleus is denoted by n = 1, n = 2, n = 3, and so on. This symbol is called quantum numbers. Bohr's atomic model shown in Figure 1.15. The letters K, L, M, and so on are used to express the trajectory of the electrons in the surrounding atomic nuclei. Trajectory with n = 1 is called the K shell, the trajectory with n = 2 is called the L shell, and so on.
Basic and excited state energies
An atom is said to have the lowest energy or stable if the electrons are in the ground state. Ground state for hydrogen atom if the electron is located on the skin, n = 1. Circumstances where n> 1 for otherwise unstable hydrogen atom, a condition called excited states. This situation occurs when a hydrogen atom absorbs energy of (Δn) hv. In the excited state, electrons are returned to the original skin is accompanied by emission of energy (Δn) hv. When the electrons return to lower skin will form a spectrum. Consider Figure 1.16.
Bohr's idea of ​​an electron around the nucleus in shells