21.6. References http://www.ck12.org
22.4 References
- Joy Sheng. CK-12 Foundation. CC BY-NC 3.0
- Hana Zavadska and Zachary Wilson. CK-12 Foundation. CC BY-NC 3.0
- Joy Sheng, using data from http://en.wikipedia.org/wiki/PH_indicator. CK-12 Foundation. CC BY-NC 3.0
- User:Datamax/Wikimedia Commons. http://commons.wikimedia.org/wiki/File:PH_Meter.jpg. Public Do-
main - User:Midnightcomm/Wikimedia Commons. http://commons.wikimedia.org/wiki/File:Antacid-L478.jpg. CC
BY 2.5 - Image copyright i4lcocl2, 2014. http://www.shutterstock.com. Used under license from Shutterstock.com
- Zachary Wilson. CK-12 Foundation. CC BY-NC 3.0
- Laura Guerin. CK-12 Foundation. CC BY-NC 3.0
- Laura Guerin. CK-12 Foundation. CC BY-NC 3.0