Michael S. answered • 08/05/26
B.S. in Chemistry, Indiana University; Organic Chem Teaching Intern
Statement 5 is the false one. A procedure should not contain inferences about what an observation means.
The distinction it is testing is between an observation and an inference, and it is worth getting straight because it comes up all year.
An observation is what your senses or your instruments actually register: the solution turned blue, a gas evolved, the mass read 4.68 g. An inference is your interpretation of it: a copper complex formed, the reaction went to completion. Two chemists watching the same beaker should record identical observations and may reasonably disagree about the inference.
A procedure is a set of instructions, written so that someone who has never seen your experiment can reproduce it exactly. It tells the reader what to do, in what order, with what quantities, and what to record. Interpretation belongs in the analysis or conclusion, after the data exist. Putting it in the procedure causes two real problems: it tells the next person what they are supposed to see, which biases what they report, and it bakes your conclusion into the method before you have collected any evidence for it.
The other four are all true, and each for its own reason:
1. Multiple values for the one independent variable. Two data points can be joined by a straight line no matter what the underlying relationship is. Several levels are what let you see the shape of the trend and notice when something is not linear.
2. Multiple constants or controlled variables. Anything you do not deliberately hold fixed is free to vary and become an alternative explanation for your result. Controls are what earn you the right to attribute the change to your variable.
3. Only one independent variable. Change two things at once and a difference in the outcome cannot be assigned to either. This is confounding, and no amount of careful measurement afterwards repairs it.
4. Both qualitative and quantitative data. Numbers are not the only evidence. A colour change, a precipitate, an odour, an unexpected temperature rise are all real data, and they are frequently what tells you something went wrong in a run whose numbers look perfectly reasonable.
A quick way to check yourself on questions like this: read each statement and ask what would go wrong if you did the opposite. For 1 through 4 the answer is an experiment you cannot draw a conclusion from. For 5 the opposite, keeping interpretation out of the procedure, is simply good practice, which is how you know 5 is the odd one out.
