Repairing a Run-On Sentence in a Lab Report
A student writes this sentence in a lab report: 'The solution turned cloudy after we added the acid it stayed cloudy for ten minutes then it cleared which showed that the reaction had finished.' A peer reviewer marks it as a run-on and says the fix is 'just add some commas'. The student also uses 'which' to refer to the whole preceding event, and the teacher has previously warned the class about vague pronoun reference.
1. Explain why adding commas alone will not fix the sentence, and identify the separate clauses it contains.
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Adding commas will not fix the sentence because the problem is structural, not punctuation. The sentence strings together several independent clauses with no conjunction and no sentence boundary. Commas alone would produce a comma splice, which is still an error.
The independent clauses are:
- 'The solution turned cloudy after we added the acid'
- 'it stayed cloudy for ten minutes'
- 'then it cleared'
There is also a dependent relative clause, 'which showed that the reaction had finished', attached to the third clause.
The fix is to separate the independent clauses with full stops (or semicolons, or coordinating conjunctions). For example: 'The solution turned cloudy after we added the acid. It stayed cloudy for ten minutes, then cleared. This showed that the reaction had finished.' Note that 'this' replaces 'which' so the reference is explicit.
2. Rewrite the sentence as two or three correct sentences, and explain how you resolved the vague 'which'.
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A corrected version: 'The solution turned cloudy after we added the acid. It remained cloudy for ten minutes and then cleared. This change showed that the reaction had finished.'
How the problems were resolved:
- Run-on: the string of independent clauses is now split into separate sentences with full stops.
- Vague 'which': in the original, 'which' could refer to the clearing, the ten minutes, or the whole event. The revision replaces it with 'This change', which points clearly to the clearing as the evidence.
- Clarity: 'stayed cloudy' becomes 'remained cloudy' for a more formal register, and 'then' is joined with 'and' so the sequence is smooth.
The principle: a relative pronoun should have one obvious antecedent. If a reader could ask 'which what?', rewrite with a noun phrase such as 'this change' or 'this result'.