List and describe two differences between pure substances and mixtures. Check all that apply. Check all that apply. The composition of a pure substance depends on the source, but the composition of a mixture doesn't depend on the source. The composition of a pure substance is always the same, regardless of the source, but the composition of a mixture can vary. The state of a pure substance is always the same, but the state of a mixture can vary. Mixtures can be separated into their components only by chemical changes; some pure substances can be separated into components by physical change. Mixtures can be separated into their components by physical changes; some pure substances can be separated into components by chemical change.