Chemistry PresentationStandards 9a and 9bExperimentation

Standard 9a and 9b Plan and conduct a

scientific Investigation to test a hypothesis.

Evaluate the accuracy and reproducibility of data

What does the word hypothesis mean? Hypothesis is an educated guess. It has to be something you can test not

just an opinion Example: Cold water freezes faster

than hot water.

There are 3 types of variables in an experiment. Control variable: variables that are kept

the same throughout the whole experiment.

Independent variable: Also called the experimental variable or manipulated variable. It is the thing the scientist is changing.

Dependent variable: what the scientist is measuring. It responds to what is being done with the experimental variable.

A good experiment only tests 1 variable at a time It’s important to test 1 variable at a time

so you know exactly what is causing your results.

Doing an experiment more than once is good. Experiments need to have reliable data

so that good conclusions can be made. Reproducibility is when you repeat an

experiment or measurement the same way you get the same answer.

Multiple trials help ensure reproducibility because errors can be seen more easily.

Your turn: Read the Following procedure carefully

EXPERIMENTAL PROCEDURE

Fill 3 containers with 300 milliliters of cold tap water.

2. Add 10 grams of salt to container 1; stir. Add 20 grams of salt to Container 2; stir. Add no salt to container 3.

Place the 3 containers in a freezer. Check the containers every 15 minutes.

Record your observations.

What is the experimental variable? EXPERIMENTAL PROCEDURE   Fill 3 containers with 300 milliliters of cold

tap water. 2. Add 10 grams of salt to container 1; stir.

Add 20 grams of salt to Container 2; stir. Add no salt to container 3.

Place the 3 containers in a freezer. Check the containers every 15 minutes.

Record your observations.

What is probably the dependent variable? EXPERIMENTAL PROCEDURE   Fill 3 containers with 300 milliliters of cold

tap water. Add 10 grams of salt to container 1; stir. Add

20 grams of salt to Container 2; stir. Add no salt to container 3.

Place the 3 containers in a freezer. Check the containers every 15 minutes.

Record your observations.

What is a control variable? EXPERIMENTAL PROCEDURE   Fill 3 containers with 300 milliliters of cold

tap water. Add 10 grams of salt to container 1; stir. Add

20 grams of salt to Container 2; stir. Add no salt to container 3.

Place the 3 containers in a freezer. Check the containers every 15 minutes.

Record your observations.

What is a possible hypothesis? EXPERIMENTAL PROCEDURE   Fill 3 containers with 300 milliliters of cold

tap water. Add 10 grams of salt to container 1; stir. Add

20 grams of salt to Container 2; stir. Add no salt to container 3.

Place the 3 containers in a freezer. Check the containers every 15 minutes.

Record your observations.

Where is there a possible error?Freezing Time Results

Trial 1 Trial 2 10 grams 10 minutes 13 minutes 20 grams 13minutes 13

minutes No salt 8 minutes 8

minutes