Assume the molar absorptivity (ε) for CoCl42- at 700 nm is 446.9 M-1 cm-1. If d, the cell path length, is equal to 0.71 cm for the cuvettes being used, and if the measured absorbance (A) at 700 nm is 0.935, what is [CoCl42-]?

Answer : The concentration of [CoCl₄]²⁻ is,

Explanation :

Using Beer-Lambert's law :

where,

A = absorbance of solution  = 0.935

C = concentration of solution = ?

l = path length = 0.71 cm

= molar absorptivity coefficient =

Now put all the given values in the above formula, we get:

Therefore, the concentration of [CoCl₄]²⁻ is,

b is the correct

alkaline metals are lithium, sodium, rubidium, potassium, cesium and francium.

alkali metals have electronegativity from 0.7 to 1, lowest in periodic table of elements, which means that alkali metals (i group in periodic table) has positive oxidation number in compounds.

electronegativity is a chemical property that describes the tendency of an atom to attract a shared pair of electrons towards itself.

alkaline metals (far left in main group) have lowest ionizations energy and easy remove valence electrons,

for example, potassium is the alkali metal and has a single valence electron in the outer electron shell.

electron configuration of potassium is: ₁₉k 1s²2s²2p⁶3s²3p⁶4s¹.

they can not exist alone in nature, because they are very reactive.