Carminic acid, a naturally occurring red pigment extracted from the cochineal insect, contains only carbon, hydrogen, and oxygen. it was commonly used as a dye in the first half of the nineteenth century. it is 53.66% c and 4.09% h by mass. a titration required 18.02 ml of 0.0406 m naoh to neutralize 0.3602 g of carminic acid. assuming that there is only one acidic hydrogen per molecule, what is the molecular formula of carminic acid?

C₂₂H₂₀O₁₃

Explanation:

In a reaction of neutralization, an acid and a base must react to form salt and water. The ions OH⁻ of the base must react with the ions H⁺ of the acid. If there is only one hydrogen acid, it means that the number of moles of OH⁻ and H⁺ must be the same, or the number of moles of NaOH and the acid is the same.

If the concentration of NaOH is 0.0406 mol/L, to find the number of moles we need to multiply it by the volume (18.02 mL = 0.01802 L)

n = 0.0406x0.01802 = 7.32x10⁻⁴ mol

The molar mass of the carminic acid is the mass divided by the number of moles, so:

MM = 0.3602/7.32x10⁻⁴

MM = 492 g/mol

The composition is 53.66% of C, 4.09% of H and 42.25% of O, so it means that the mass corresponding of these atoms in one mol are:

C = 0.5366x492 = 264 g

H = 0.0409x492 = 20 g

O = 0.4225x492 = 208 g

Knowing the molar masses (C = 12 g/mol, H = 1 g/mol, O = 16 g/mol), the number of atoms on one mol of the acid is:

C = 264/12 = 22

H = 20/1 = 20

O = 208/16 = 13

So the molecular formula is C₂₂H₂₀O₁₃

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.