1. Heat always flow from a region of higher temperature
to a lower temperature, just like concentration gradient. So in this case,
since the metallic sphere is hotter than water, so naturally heat energy flows
from the metallic sphere to the water.
2. We use the formula:
Q = m C ∆T
where Q is the heat energy gained, m is mass of water, C
is heat capacity of water = 4.184 J/g°C and ΔT is change in temperature
Since density of water is 1 g/mL, so mass is also 100g,
therefore:
Q = 100 g * 4.184 J/g°C * (27.1°C - 25°C)
Q = 878.64 J
3. Heat gained by the water is equal to the heat lost by
the metal, therefore:
Q(water) = - Q(metal)
878.64 J = - 15 g * C * (27.1°C - 98°C)
C = 0.83 J/g°C
Answer:
The correct answer is:
<em>(1) It is important that the sample is dissolved in just enough hot solvent. </em>
Explanation:
The process of recrystallization is important to eliminate the impurities and to obtain better crystals of the solid. The solvent used to perform the recrystallization must have a high dissolution power of the substance to be recrystallized and a low dissolution power of the impurities. This is in order to eliminate most impurities. Furthermore, <em>It is important that the sample is dissolved in just enough hot solvent </em>because this should be easy to remove after the recrystallization and the crystal should form easily when the solution cools. Also, it is better to add the hot solvent to solubilize the crystals and keep the impurities insoluble, instead of adding the cold solvent and heating the solution. Additionally, the process of cooling the solution must be done slowly to obtain large and fewer crystals. A fast ice-cooling will form smaller crystals.
The alkali metals are so reactive that they are never found in nature in elemental form. Although some of their ores are abundant, isolating them from their ores is somewhat difficult. For these reasons, the group 1 elements were unknown until the early 19th century, when Sir Humphry Davy first prepared sodium (Na) and potassium (K) by passing an electric current through molten alkalis. (The ashes produced by the combustion of wood are largely composed of potassium and sodium carbonate.) Lithium (Li) was discovered 10 years later when the Swedish chemist Johan Arfwedson was studying the composition of a new Brazilian mineral. Cesium (Cs) and rubidium (Rb) were not discovered until the 1860s, when Robert Bunsen conducted a systematic search for new elements. Known to chemistry students as the inventor of the Bunsen burner, Bunsen’s spectroscopic studies of ores showed sky blue and deep red emission lines that he attributed to two new elements, Cs and Rb, respectively. Francium (Fr) is found in only trace amounts in nature, so our knowledge of its chemistry is limited. All the isotopes of Fr have very short half-lives, in contrast to the other elements in group 1.
The balanced chemical reaction is:
2KClO3 ----> 2KCl + 3O2
We are given the amount of oxygen gas to be produced from potassium chlorate. This will be the starting point for the calculations.
28.0 L O2 ( 1 mol / 22.4 L) (2 mol KClO3 / 3 mol O2) ( 122.55 g / 1 mol) = 102.13 g KClO3 is needed
The burning of methane gas, given below, is a redox reaction. which part of the reaction illustrates oxidation, Ch4+O2---CO2+H2O<span>CH4---CO2</span>