BASIC CHEMISTRY 1 MID TEST

RENI DESRINOFITA
RSA1C112006

1. X pure material is solid at room temperature. if the substance is heated to 230 C melted gradually. if it is then cooled to room temperature, the liquid can not be frozen.
   a. that x may be from an element or compound. explain it!
   b. Is it a chemical change occurs? if so could be said to undergo change endotherm, based on the information provided?
  c.can said that the liquid is an element, based on the information providedAnswer:

  a. X in the above matter is a compound, because the compound is a combination of several elements that have the same properties.While the element is a collection of some of the same atoms that have the same properties, because the number of neutrons is the same. In the matter of the above mentioned that the substance melted at some stage, while the elements that can not be divided again with any chemical reaction, so we can conclude that X is a compound.

  b. In the X chemical changes, because chemical changes occur when marked by several changes, such as changes in color, temperature, precipitation occurs and there are gas bubbles. In X temperature change from room temperature is at 25 C to 230 C means the X chemical changes.The reaction involves the endothermic reaction into endothermic reactions occur because the temperature change of the environment to the system.

  c. Yes, because it is a constituent element of a compound. Based on the above information, including fluid into the elements, because water is a constituent element of H and O.

2. When the candle that weighs 10 g burned in oxygen, carbon dioxide and water vapor formed by the combustion of more than 10 g weight. This was the case in accordance with the law of conservation of mass. Explain!Answer:
Law of conservation of mass expressed by Antoine Laurent Lavoisier (1743-1794), which reads: "In a reaction, the mass of substances before and after the reaction is the same", in other words, the mass can not be created and can not be destroyed. This means that as long as there is no reaction occurs atoms reactants and reaction products were missing.Understanding different mass with weight terms. The mass of an object, in all places always remain, while the severity depends on the local force of gravity.In the above case before the burning substance is 10 g weight while after severe reaction to a substance into 10 g more, so that changes is the weight of the substance but its mass will not change.
3. When carbon burns under a limited amount of oxygen, it forms two gaseous compounds. Suggest ways to diffrerentiate two compounds with one another.Answer:
Doing qualitative research or experiments of the experiment we can find the difference between the two gas.Or it can also be determined by determining the constituent elements of the substances we eat will know the difference of the two substances.
4. After mendeev preparing the periodic table, he concluded that the atomic weights of some elements was the wrong decision, and this conclusion appears to be true. How mendeelev able to predict some of the atomic weights is wrong? why his predictions are not always right. Explain!Answer:

In 1869 a Russian scholar named Dmitri Ivanovich Mendeleev, based on observations of 63 elements known at the time, concluded that the properties of elements are a periodic function of the relative atomic mass. That is, if the elements are arranged according to their relative atomic mass increases, the specific properties will be repeated periodically. Mendeleev placed elements that have similar properties in vertical columns called class. Row-column horizontal line element that increases the relative atomic mass, called the Mendeleev periodic period in 1872 published a list displayed on the table.
Many other elements grouping ideas proposed but did not satisfy the scientific community at the time. However, the theory proposed by Dmitrij Ivanovich Mendeleev Russian chemist (1834-1907), and independently by the German chemist Julius Lothar Meyer (1830-1895) in contrast to other proposals, and more persuasive. Both have the same outlook as follows:
The views Mendeleev and Meyer
List the elements that exist at that time may not be comprehensive.
Expected properties of elements vary systematically. So the nature of the element of the unknown can be predicted.
Originally Mendeleev theory failed to attract attention. However, in 1875, indicated that the new element gallium was discovered by French chemist Paul Emile Lecoq de Boisbaudran (18,381,912) was not the other is the existence of eka-aluminum and its been predicted by Mendeleev. Thus, the significance of the theory of Mendeleev and Meyer slowly accepted. Table 5.2 provides properties for elements predicted by Mendeleev, who was not yet known and the nature of germanium ekasilikon discovered by German chemist Clemens Alexander Winkler (1838-1904).

Mendeleev published a table that can be considered as the origin of the modern periodic table. In preparing the table, Mendeleev initially arrange the elements in order of atomic mass, as well as its predecessor. However, he stated keperiodikan nature, and sometimes reorder the elements, resulting in reverse order of atomic mass.
Furthermore, the situation is complicated because the procedure to determine the mass of the atom has not been standardized, and sometimes chemist might use a different atomic mass for the same element. This dilemma is slowly resolved after the International Chemical Congress (Congress was held in 1860 in Karlsruhe, Germany. Goal of the Congress is to discuss the unification of atomic mass. Cannizzaro to take this opportunity to introduce Avogadro's theory.) First attended by Mendeleev, but difficulties remains.The periodic table is continuously growing element after Mendeleev periodic table is proposed. Meanwhile, there is a variety of problems. One important issue is how to handle the noble gases, transition elements and rare earth elements. All these issues are properly resolved and made the periodic table are more valuable. The periodic table, chemical scripture, should be referred to regularly.
New class of noble gases easily inserted between the positive elements that are highly reactive, alkali metals (group 1) and negative elements are very reactive, halogen (group 7).
Accommodated the transition metal element in the periodic table by inserting a long period although not very clear rationale. The real problem is lantanoid. Lantanoid treated as an element of the "extras" and placed marginally outside the main part of the periodic table. However, the actual procedure does not resolve the main problem. First, why is there an extra element is unclear, even more of a puzzle is the question: is there a limit of the number of elements in the periodic table? Because there are elements that are very similar, it is difficult to decide how many elements can exist in nature.
Bohr theory and experiment Moseley generate theoretical resolution of these problems. Explanation of the periodic table of the first period to the third period can be explained by the theory of electron configuration described in chapter 4. The first period (1H and 2HE) associated with the process of entering the 1s orbital. Similarly, the second period (from 3Li to 10Ne) associated with filling the 1s, 2s and 2p, and the 3rd period (from 11Na to 18Ar) associated with filling the 1s, 2s, 2p, 3s and 3p.
Period begins the period-4. The explanation for this is due to their drastically different d orbitals of the circle, and so the 3d electron energies even higher than 4s. Consequently, the period-4, the electrons will fill the 4s orbital (19K and 20Ca) as soon as the 3s and 3p orbitals, 3d orbitals jump. Then the electrons begin to occupy the 3d orbitals. This process is related to the ten elements of 21Sc to 30Zn. The process further 4p orbitals are related to the six elements of 31Ga to 36Kr. This is the reason why the period-4 contains 18 elements instead of 8. 4f electron orbital energies much higher than 4d orbitals and thus the 4f electrons do not play a role in the period of the four elements.
Period-5 is similar to the period-4. The electrons will fill orbitals 5s, 4d and 5p in this order. As a result, the period-5 will have 18 elements. 4f orbitals are not involved and this is the reason why the number of elements in the 5 is 18.
The number of elements to be included in period-6 are 32 reasons involved 7 × 2 = 14 elements related to the 4f orbitals. Originally 6s electrons fill orbital (55Cs and 56Ba). While there are miraculous exceptions, elements from 57La to 80Hg associated with 4f orbitals and then 5d. Lantanoid series (up 71Lu) rare earth elements associated with the 4f orbitals. After this process, the six main group elements (81Tl to 86Rn) to follow, this is related to 6p orbitals.
Period-7 began with the 7s orbitals (87Fr and 88Ra) followed by the 5f orbitals produce aktinoid series of rare earth elements (from 89Ac to element No. 103). World elements will spread further, but in between the elements that exist naturally, the element with the largest atomic number is 92U. Elements after 92U is made elements with a very short half-lives. It is difficult to foresee an extension of this kind of list elements, but it is likely the new element will be very short half-life.

5. When the mercury chloride solution is added a solution of silver nitrate, a white solid forms. Identification of a white solid and write a balanced equation for the reaction that occursAnswer:

HgCl2 + 2AgNO3 ---> Hg (NO3) 2 + 2AgClThe resulting white powder is silver nitrate (AgNO3)