Question

questions 6 refers to the scenario below.
in the lab, a quality assurance chemist is working with sodium bicarbonate, nahco₃, which is commonly known as baking soda. it is a white crystal which we typically see in powdered form. the chemist must test the sample for purity to make sure it does not contain any other substances that would make it unsafe for consumption, since this sodium bicarbonate will be used as an active ingredient in antacid medication.

1. the scientist finds that the solution conducts electricity. this partly happens because in water, the sodium (na) atoms separate from the bicarbonate (hco₃). which particle diagram represents a pure substance which, like sodium, also cannot be broken down further by physical or chemical means?

(a)
(b)
(c)
(d)
key
○ = atom of one element
● = atom of a different element

Explanation:

A pure substance that cannot be broken down further by physical or chemical means is an element. In the key, each circle (whether white or black) represents an atom of an element. Option A shows only one type of element (all - white circles). Option B shows two different elements (white and black circles) but as separate diatomic molecules. Option C shows a compound (a combination of two different elements in a fixed ratio). Option D also shows a compound. Since we are looking for a pure substance (an element), and Option A has only one type of element - based on the key (white circles representing atoms of one element), Option A is correct.

Answer:

A.