A mass noun (sometimes called a noncount noun) is one that denotes something uncountable, either because it is abstract {cowardice} {evidence} or because it refers to an indeterminate aggregation of people or things {the faculty} {the bourgeoisie}; the latter type is also called a collective noun. As the subject of a sentence, a mass noun usually takes a singular verb.
But in a collective sense, it may take either a singular or a plural verb form.
A singular verb emphasizes the verb; a plural verb emphasizes the individual members.
Which verbs are correct?
Mass nouns are sometimes followed by a prepositional phrase, such as number of plus a plural noun. The article that precedes the mass noun signals whether the mass noun or the number of the noun in the prepositional phrase controls the verb. If a definite article (the) precedes, the mass noun controls, and typically a singular verb is used.
If an indefinite article (a or an) precedes, then the number of the noun in the prepositional phrase controls.
Source: The Chicago Manual of Style, 16th edition.