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.
Answer:
81.0°C
Explanation:
<em>Kb benzene = 2.5°C/m</em>
<em />
The addition of a solute to a pure solvent produce an elevation in boiling point regarding to boiling point of pure solvent. This phenomenon follows the equation:
ΔT = Kb×m×i
<em>where ΔT represents the increasing in boiling point, Kb is the elevation boiling point constant of the solvent (2.5°C/m for benzene), m is molality of solution (Moles solute / kg solvent) and i is Van't Hoff factor (1 for a non-electrolyte solute as naphthalene).</em>
<em />
Moles of 11.5g of naphthalene (Molar mass: 128.17g/mol) are:
11.5g × (1mol / 128.17g) =<em> 0.0897 moles of naphthalene in 250.0g = 0.250kg of benzene.</em>
Molality is:
0.0897 moles of naphthalene / 0.250kg of benzene = 0.359m
Replacing in the equation:
ΔT = Kb×m×i
ΔT = 2.5°C/m×0.359m×1
ΔT = 0.90°C
That means the solution prepared has an elevation in boiling point of 0.90°C. As boiling point of pure benzene is 80.10°C, boiling point of the solution is:
80.10°C + 0.90°C =
<h3>81.0°C</h3>
The pH of the solutions given are:
- Oven cleaner- 13
- Water- 6.15
- Blood- 7.39
- Vinegar- 2.20
The pH can be defined as the hydrogen ion concentration of the solution. The pH can be calculated as the negative log of the hydrogen ion concentration in the solution.
<h3>What is the pH of solutions?</h3>
The pH can be calculated as:
The pH of the following solutions is given as;
The pH of the oven cleaner is:
The pH of the oven cleaner is 13.
The pH of a water sample is:
The pH of the water sample is 6.15.
The pH of the blood sample is:
The pH of the blood sample is 7.39.
The pH of the vinegar is :
The pH of the vinegar sample is 2.20.
Learn more about pH, here:
brainly.com/question/491373
Answer: bacteria, archaea, plants, protists, animals, and fungi
Explanation: Throughout the history of evolution, cellular respiration has been a central element of many organisms' functioning. Even as species have developed and changed through the process of natural selection, all of the successful, surviving individuals have kept the genes that allow them to produce the enzymes needed for cellular respiration.
It tends to decrease! :(
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