MID CHEMISTRY TEST

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 provided Answer:
  
a.X is the element (sulfur), because at temperatures below 95.5 C he would stabilyang dinamakn rombik sulfur was the temperature is above him akn kristaldan transformed into monoclinic form, so that does not freeze at room temperature is monoclinic sulfur because he akn stable and frozen at temperatures above 95.5 C while rombik not. 
b. Chemical changes that occur are changes in the endothermic reaction because the element X to convert solid to liquid heat transfer resulting from the environment to the system (heat absorbed by the system from its environment), a marked drop in the ambient temperature around the system. 
c. Yes, because the fluid including elements At room temperature (25 C) elements can be solid, liquid or gas, and the elements of X changes as heated 

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:because the wax that has mass of 10 grams when it reacts with oxygen to form water and carbon dioxide, the mass of wax will react with oxygen mass and it will add weight to the results obtained are water and oxygen. 

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:to distinguish compounds resulting from one compound to another compound, is to look at the properties of chemical, odor, and color can also denagn if distinguish compounds resulting from the burning of carbon with oxygen was also reacting carbon monksida bias (CO) with lime water ( Ca (OH) 2), and carbon dioxide (CO2) with lime water, the carbon monoxide can not react, while the carbon dioxide will memebentuk calcium carbonate (CaCO3) 

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.
As can be seen in the picture above, Mendeleev mengkosongkan some places. This is done to establish the nature of equality in the classroom. For example, placing Mendelev Ti (Ar = 48) in group IV and group III were left empty because Ti is more similar to C and Si, compared with B and Al. Mendeleev predicted the properties of elements that have not known it. Estimates are based on the nature of the other elements that have been recognized, which is adjacent either horizontally or upright. If these elements are predicted to have been found, is in accordance with the predictions Mendeleev. One example is germanium (Ge), which was found in 1886, which Mendeleev called ekasilikon.The weakness of this theory is still contained elements of a larger mass that lies in front of a smaller mass elements. Co: Tellurium (te) = 128 in kiriIodin (I) = 127. this is because the elements have properties kemirpan placed in one class. The weakness of this theory is the atomic mass correction. Previous atomic mass. In previous atomic mass = 76-113. besides Be, 13.5 to 9. N 120-240.The advantage is forecasting a new element predictable elements and their properties. 

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 occurs

 Answer:HgCl2 + 2AgNO3 ---> Hg (NO3) 2 + 2AgCl 
The resulting white powder is (AgCl)