1. Chemistry Presentation Standards 9a and 9b Experimentation

2. Standard 9a and 9b  Plan and conduct a scientific Investigation to test a hypothesis.  Evaluate the accuracy and reproducibility of data

3. 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.

4. 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.

5. 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.

6. 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.

7. 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.

8. 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.

9. 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.

10. 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.

11. 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.

12. Where is there a possible error? Freezing Time Results Trial 1Trial 2  10 grams 10 minutes 13 minutes  20 grams 13minutes 13 minutes  No salt 8 minutes8 minutes