To make sure experiments are reliable you should ensure that the glassware that you are using is clean and uncontaminated.
Choosing the right equipment is important. If you only have a small amount of material then a test tube is useful. Beakers or conical flasks are better for larger volumes of liquid.
Valid means that you are testing what you think you are testing. You must make sure that you are testing the hypothesis you started with and not some other hypothesis.
Reliable means that you have not made any mistakes in your method and you have tested with repetition. Another person should be able to follow your method and get the same results.
Having more than one copy of the investigation is important in the reliability of an experiment. This can be done by replication or repetition. In this investigation replication is good to use to ensure reliability.