UTS 21 November 2011
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 a candle that weight 10 g 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.
answer : law of conservation of mass says that the mass before and after the reaction is the same. The mass of wax in the fuel will be equal to the mass of wax before the fire. The melted wax is still wax, which changed its form only. Candles will be burning the gas and the amount of energy (heat and light). If the result of burning accommodated and weighed, surely its mass equals the mass plus the mass of oxygen candles are used on burning it.
Answer : How to distinguish the two compounds with one another by adding a non-polar compounds or compounds that make reaching saturation point state.
4. After medelev compiled the periodic table, he conclude that the atomic weight of certain element was wrong ruling, and this conclusion was apparently correct. How mendelev was able to predict that several atomic weight were wrong ? why his prediction are not always right?
Answer : In 1869, Dmitri Ivanovich Mendeleyev Russian chemist nationality arrange 65 elements known at that time. Mendeleev sort the elements of increasing atomic mass and chemical properties
At the same time, Julius Lothar Meyer made arrangement of elements such as the dikernukakan by Mendeleyev. Only, Lothar Meyer arrange these elements based on their physical properties. Although there are differences, but both produce the same grouping of elements.
Mendeleyev provide an empty box to place the elements that time it has not been found, such as elements with mass numbers 44, 68, 72, and 100. 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 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.
Answer : HgCl2 + 2AgNo3 àHg(No3)2 + 2AgCl
White solid : AgCl
