MID TEST

UTS 14,NOVEMBER 2012

 1.      pure substance X is solid at room temperature. if the substance is heated to 230 ℃ 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 :          X is a compound. The compound is a collection of several elements. If a compound in the melt by the heat will melt easier. But it will be difficult molten liquid solidifies at the same temperature setting before him in the melt. If you want to make it freeze then the need is even lower temperatures. It may be a temperature below 0 ℃.

b)      does it a chemical change occurred ? if so can it be said to undergo an endotherm changing, based on the information provided?

answer :          chemical changes that occur can be called endothermic reactions. Endothermic reaction is a reaction that is accompanied by heat transfer from the environment to the system (heat absorbed by the system from its environment); characterized by a decrease in ambient temperature around the system. Substance X which initially are solid when heated at a temperature of 230 ℃ to melt in the heat in the environment caused due to move to the substance, so that the substance to be melted and the temperature in the substance becomes higher than
the temperature of their environment.

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

answer :             there are elements which are in fluid. For instance mercury. But based on the information that is given me to say that it's open compound elements.




2. When the wax weight of 10 grams burned in oxygen, carbon dioxide and water vapor formed by the combustion weigh more than 10 grams. Is this game any case law of mass. Explain.

The answer is:
 Including the law of mass eternity (lavoiser) burned candles will melt and when cooled again will freeze again, in the process also formed wax pembekaran Co2 + H2O in the form of gas, it was the cause of the change in mass before and after the burn bkar, but if the count is its chemical calculations should no striking difference in the mass before and after the fuel is burned.


3. When carbon burns oxygen with kimited number, will form two gas compounds. Suggest a way to differentiate the two compounds with one another?
the answer is:
 was about the enthalpy of combustion ...
Her compound is Karb on dioxide and water,
How to distinguish is because each process will generate the combustion gases are CO2 + 2 H2O,
while the incomplete combustion CO + H2O.
 more details are to distinguish the two compounds with one another by adding a non-polar compounds or compounds that make the state reached saturation point.

 4. After mendeev compiled theperiodic table, he concluded that the atomic weights of some elements was the wrong decision, and this conclusion appears to be true. How Mendeleev able to predict that the atomic weight of some wrong? Why predictions are not always right. Explain!
the Answer is:

 conclusions do seem true
Medeleev because taking the average total value of the four elements to determine the elements sought.
According to Mendeleev,
"If there is a particular group of elements, R1, R2, R3, and if some elements of R2 are elements of Q2 and T2, then the properties of R2 is determined by the average properties of the R1, R3, Q2 and T2"
why ramalanya is not always true. because the difference between the masses is not always 2, but the range of 1 and 4
 OR
  Mendeleyev had predicted the properties of elements and it is a prophecy after the elements were found. Arrangement of the elements of Mendeleev perfected under the law and called Mendeleev periodic system.
Mendeleev periodic system consisting of groups (elements located in a single column) and period (the elements which lie on one line)



5.. When mekuri chloride solution is added to a solution of silver nitrate, a white solid forms. Identification of a white solid and write a balanced equation for the reaction.?
the answer is
  Sediment on the results of a white precipitate of silver nitrate ..
her reksih
Hg2CL2 AgNO3 ------ + Hg (No3) 2 + HgCl2
equalization reraksi
HgCl2 + 2AgNo3 = HG (No3) 2 + 2AgCl
White solid: AgCl