In this activity, students will develop an understanding of why significant figures are important in chemistry and learn how to determine the number of significant figures in a measurement.
This activity will help prepare your students to meet the performance expectations in the following standards:
- Scientific and Engineering Practices:
- Using Mathematics and Computational Thinking
By the end of this activity, students should be able to
- Understand that numbers presented in chemistry are all measurements.
- Be able to determine the number of significant figures in a given measurement.
This activity supports students’ understanding of
- Significant figures
- SI units
Teacher Preparation: 30 minutes
Lesson: 60 minutes
- Student Handout
- Optional Items for Visuals:
- Various Balances
- No specific safety precautions need to be observed for this activity.
- The POGIL website is a great resource for additional helpful information regarding using guided inquiry.
- This activity is designed as a student-centered strategy, where the students work in small groups to ensure all students are fully engaged in the learning process.
- For this activity, I suggest organizing students into groups of 4. It is helpful if you can place a strong student in each group.
- The students will be working through the student handout from the beginning to the end, there is no skipping questions.
- The activity is designed to guide the students. They will consider the information presented in the first box, then use it to draw conclusions and making inferences. Next they will apply and synthesize this information.
- It is important that the teacher takes the time to explain the process so that students understand how to navigate the activity.
- Tell the students that they need to work as a group. No one should be left behind, as they work at the pace of the slowest group member.
- Teachers should try to not answer any questions during the activity. Encourage the students to figure out what the question is asking and how to answer it. Go over all the answers when all the groups are done (answer key is included).
- You should walk around the classroom while the students are working, listen to their conversations, but do not answer any questions.
- It is hard to get students to buy into the process at first but if you force them to try it they will enjoy it and get a lot out of it.
- This activity can be successfully used as an introduction to significant figures, or as a review activity.
For the Student
In science, the uncertainty of a measurement is very important when we obtain and record measurements in the lab. It is important to remember that all of the numbers that we deal with in chemistry come from data in a lab. This means that the numbers always have units associated with them and there is some uncertainty associated with the measurement. Uncertainty can come from error or uncertainty of the equipment. When you are taking measurements, the measurement should always be taken to the point where you have to estimate, when you do this all the numbers recorded will be significant.
The most important thing to remember about chemistry is that all the numbers we use come from lab data, so we need to be able to determine the significance of the numbers.
What is the difference between these values?
By the end of this activity you should be able to determine how many significant figures are in a given number.
Remember numbers taken in the lab are measurements.
All digits from a measurement are significant.
Always measure to the point of uncertainty.
- Using the ruler below determine the measurement in each example. Explain your reasoning for each one.
- A balance was used to find the mass of an object. Review the recorded masses below, which one measures an object to a mass one tenth a gram? Which one measures an object to a mass one thousandth a gram? Explain your reasoning.
|a. 0.1 g||b. 0.10 g||c. 0.100 g|
- You go to a bulk candy store to buy some candy (you have had a very tough week). The candy is priced per pound (and you don’t have a lot of money). For 1 pound of candy the price is $5.98. You decide you want to by a half pound of candy because you only have three dollars. Which balance (listed above in question #2) would you rather use to make sure you get the most candy for your money? Explain your reasoning.
- How many zeros are crossed out in A, B, C, D?
- What numbers are not crossed out in A, B, C, D?
- Why are the arrows for A and B pointing to the right?
- Why are the arrows for C and D pointing to the left?
- Can you draw a conclusion about the position of the decimal and how the arrow is drawn?
- Determine the number of significant figures in the following numbers.
Number of Significant Digits
|g. 30.0 x 102|
|h. 1000 x 10-3|
- Create rules for determining the number of significant figures in a value: