Developing a research question is an important part of the writing process so that you have a plan for how your paper will come together. Part of the process is thinking about the terminology you need to use and the scope of the project.
For a five page research paper on Heart of Darkness, you might think about the issue of postcolonialism and imperialism.
What is postcolonialism? (Too broad, only one concept)
How are the themes of postcolonialism and imperialism expressed in Heart of Darkness? (Closer, two concepts)
How does Kurtz symbolize an imperial power in Heart of Darkness and what are the resulting postcolonial themes? (Three concepts, possibly too many?)