1. Pure substance x is solid at room temperature. if the substance 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!
b. Does it chemical change occured? if so can it be said undergo an endotherm changing, based on the information provided?
c.can it be said that the liquid is an element, based on the information provided
answer :
a. a. X because X is a compound substance has different properties with its constituent elements. Compounds can only be broken down into its constituent elements by chemical reactions. At the same conditions, the compound may have a shape different from its constituent elements. Chemical properties of different compounds with the elements of its constituent
b. b. Chemical changes that occur are changes in endothermic reaction because the compound X to change solids to liquid heat transfer resulting from the environment to the system (heat absorbed by the system from its environment); characterized by a decrease in ambient temperature around the system.
c. c. Yes, because the liquid is included elements At room temperature (25 C) elements can be either solid, liquid or gas and the elements of X changes as heated
2. When a candle that weighs 10 g is burned in oxigen, 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:
Law of conservation of mass, also known as the Lomonosov-Lavoisier law is a law that states the mass of a closed system is constant despite the wide range of processes in the system (mass of substances in closed systems before and after the reaction is the same (fixed / constant)) .
Because mass and energy-related, in a system that gets / expend energy, the mass in very small amounts will be created / lost from the system. However, in almost all events that involve changes in energy, the law of conservation of mass can be used because the mass has changed very little.
3. When carbon burns in oxygen under limited number, it will form two gaseous compounds. Suggest the way to diffrerentiate the two compounds with one another.
Answer :
Carbon monoxide CO, is a colorless gas, odorless, and tasteless. It consists of one carbon atom covalently bonded to one oxygen atom. In this bond, there are two covalent and one coordinate covalent bond between carbon and oxygen atoms.
Carbon monoxide is produced from incomplete combustion of carbon compounds, often occur in internal combustion engines. Carbon monoxide is formed when there is a lack of oxygen in the combustion process. Carbon monoxide is flammable and produces a blue flame, producing carbon dioxide. Although it is toxic, CO plays an important role in modern technology, which is a precursor of many compounds of carbon.
4. After mendeev compiled the periodic table, he concluded that the atomic weights of certain elements was wrong ruling, and this conclusion was apparently correct. How mendeelev was able to predict the several atomic weights were wrong? why his predictions are not always right. Explain it!
Answer :
In 1869 a scholar of Russian origin named Dmitri Ivanovich Mendeleev, based on observations of 63 elements known at the time, concluded that the properties of elements are periodic function of the relative atomic mass. That is, if the elements are arranged according to their relative atomic mass increases, then the specific properties will be repeated periodically. Mendeleev placed elements that have a similarity of traits in a vertical column called class. Row-column horizontal, ie lane elements of increasing relative atomic mass, called the period of the periodic Mendeleev published the list in 1872 were shown on the table.
As can be seen in the picture above, Mendeleev mengkosongkan some places. This was done to establish the similarity of the properties in the class. For example, placing Mendelev Ti (Ar = 48) in group IV and group III left empty because Ti is more similar to C and Si, than with B and Al. Mendeleev predicted the properties of the elements that have not known it. The forecast is based on the nature of other elements which are well known, adjacent either horizontally or upright. When the elements are predicted was found, it is highly in accordance with the predictions Mendeleev. One example is a germanium (Ge), which was found in 1886, which by Mendeleev named ekasilikon.
The weakness of this theory is still contained elements of a larger mass is located in front of the element whose mass is smaller. Co: Tellurium (te) = 128 in kiriIodin (I) = 127. this is because the elements that 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 to 113. besides Be, from 13.5 to 9. N from 120 to 240.
advantage is forecasting a new element that is predicted elements and their properties.
5. When an aqueous solution of merkuri chloride is added 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 ---> Hg (NO3) 2 + 2AgCl
The resulting white powder is silver nitrate (AgNO3)
