Mid Semester Test (Basic Chemistry)

1 (a) X is an element in my opinion, since we know that the elements are pure substances that can be decomposed again into other simpler substances by ordinary chemical reactions.
(b). Yes, the occurrence of physical changes in which no formation of new substances and the occurrence of endothermic reactions where the reaction requires heat energy gained or absorbed by the system of environmental
(c) yes X can be called as an element of us because they know that the elements are pure substances that can be decomposed again into other simpler substances by ordinary chemical reactions.

2. In this case does not fit with the law of conservation of mass to the sound of the mass conservation law is the 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 (in The mass of a closed system of substances before and after the reaction is the same (fixed / constant)). General statement used to declare the law of conservation of mass is the mass can change form but can not be created or destroyed. For a chemical process in a closed system, the mass of the reactants must equal the mass of the product, so if the mass is 10 grams of wax initially then after reacted with oxygen should be the result of the reaction must also be or remain 10 grams

3.The way to differentiate is with giving high energy so it can  break down so it can separate between one and other

4. Mendeleev wrote the definitive textbook of his time: Principles of Chemistry (two volumes, 1868–1870). As he attempted to classify the elements according to their chemical properties, he noticed patterns that led him to postulate his periodic table. Mendeleev was unaware of the other work on periodic tables going on in the 1860s. He made the following table, and by adding additional elements following this pattern, developed his extended version of the periodic table.^[10][11]

Cl 35.5	K 39	Ca 40
Br 80	Rb 85	Sr 88
I 127	Cs 133	Ba 137

On 6 March 1869, Mendeleev made a formal presentation to the Russian Chemical Society, entitled The Dependence between the Properties of the Atomic Weights of the Elements, which described elements according to both atomic weight and valence. This presentation stated that

1. The elements, if arranged according to their atomic weight, exhibit an apparent periodicity of properties.
2. Elements which are similar in regards to their chemical properties have atomic weights which are either of nearly the same value (e.g., Pt, Ir, Os) or which increase regularly (e.g., K, Rb, Cs).
3. The arrangement of the elements in groups of elements in the order of their atomic weights corresponds to their so-called valencies, as well as, to some extent, to their distinctive chemical properties; as is apparent among other series in that of Li, Be, B, C, N, O, and F.
4. The elements which are the most widely diffused have small atomic weights.
5. The magnitude of the atomic weight determines the character of the element, just as the magnitude of the molecule determines the character of a compound body.
6. We must expect the discovery of many yet unknown elements–for example, two elements, analogous to aluminium and silicon, whose atomic weights would be between 65 and 75.
7. The atomic weight of an element may sometimes be amended by a knowledge of those of its contiguous elements. Thus the atomic weight of tellurium must lie between 123 and 126, and cannot be 128. Here Mendeleev seems to be wrong as the "atomic mass" of tellurium (127.6) remains higher than that of iodine (126.9) as displayed on modern periodic tables, but this is due to the way atomic masses are calculated, based on a weighted average of all of an element's common isotopes, not just the one-to-one proton/neutron-ratio version of the element to which Mendeleev was referring.
8. Certain characteristic properties of elements can be foretold from their atomic weights.

Mendeleev published his periodic table of all known elements and predicted several new elements to complete the table. Only a few months after, Meyer published a virtually identical table. Some consider Meyer and Mendeleev the co-creators of the periodic table, but virtually everybody^[who?] agrees that Mendeleev's accurate prediction of the qualities of what he called ekasilicon, ekaaluminium and ekaboron (germanium, gallium and scandium, respectively) qualifies him for the majority of the credit for the table.

For his predicted eight elements, he used the prefixes of eka, dvi, and tri (Sanskrit one, two, three) in their naming. Mendeleev questioned some of the currently accepted atomic weights (they could be measured only with a relatively low accuracy at that time), pointing out that they did not correspond to those suggested by his Periodic Law. He noted that tellurium has a higher atomic weight than iodine, but he placed them in the right order, incorrectly predicting that the accepted atomic weights at the time were at fault. He was puzzled about where to put the known lanthanides, and predicted the existence of another row to the table which were the actinides which were some of the heaviest in atomic mass. Some people dismissed Mendeleev for predicting that there would be more elements, but he was proven to be correct when Ga (gallium) and Ge (germanium) were found in 1875 and 1886 respectively, fitting perfectly into the two missing spaces.

5.White solid is precipitate is produced from the reaction of silver with mercury-added nitarat in klorida.Wjich is white solid formed new properties
Equation is HgCl+AgNO3 èHgNO3+AgCl