Question

A chloride dissolves appreciably in cold water. When placed on a Pt wire in a Bunsen flame, no distinctive colour is noted. Which cation would be present?
(A) \[B{e^{2 + }}\]
(B) \[B{a^{2 + }}\]
(C) \[P{b^{2 + }}\]
(D) \[C{a^{2 + }}\]

Answer 1

Hint: In chemical reactivity series, the elements placed higher are extremely reactive and are known to even react with cold water. They are generally alkali metals and alkaline earth metals.

Complete Step by Step Solution:
Group $2$ chlorides dissolve in water but $Be$ is least dissolvable. $Be$ dissolves in cold water.

Flame test are performed in analytical chemistry for identification of compounds by their characteristic colour that is imparted to the flame. First, you need a clean wire loop. A clean platinum or nickel-chromium wires dipped in hydrochloric or nitric acid and then rinsed with distilled water. Test the cleanliness of the loop by inserting it into a gas flame. If a burst of colour is produced, the loop is not sufficiently clean. The loop must be cleaned between tests. The wire is dipped in solution of an ionic (metal) salt. The wire with the sample is placed in the clear or blue part of the flame and observes the colour.

Flame test is given by mostly alkali and alkaline earth metals. Group $1$elements lithium, sodium, potassium, rubidium, caesium give flame test of colour red, yellow, lilac, red, blue respectively. Group $2$elements calcium, strontium, barium, radium shows colour yellow-red, red, pale green crimson red respectively. Exceptions are beryllium and magnesium. Beryllium and magnesium do not show flame tests. Flame test is also given by zinc, lead and many other elements.

Magnesium chloride also dissolves in cold water but there is no option in question of magnesium. Hence, the only correct answer is A.

Option B, C and D are incorrect because they give flame tests when platinum wire is placed in Bunsen flame.

Note: It is important to keep the wire clean. To check the cleanliness, insert it into a gas flame. If a burst of colour is produced it means the wire is not sufficiently clean.