What are significant figures in chemistry?

Significant Figures Chemistry?

• My daughter is in Chemistry, and she would like some help on her homework. I have no idea what to do, because it has been too long since I was in school, how would you do these problems and what are the answers. Thank you. Express each answer to each of the following calculations with the correct number of significant figures. 1) 3.42cm + 8.13cm 2) 4.939g + 3.822g 3) 17.8cm + 12.11cm How many significant figures are there in each? 1)23 2)1.498 3)107 4)0.05587 Could you explain these in the easiest way possible, her teacher teaches things in a college level. Any help is appreciated.

• Answer:

  Significant digit rule when adding: add, cross out any numbers that don't have a matching digit to the right. 3.42 cm + 8.13 cm As you can see, there are no numbers that do not have a matching number above or below it. For this one, just add, to get 11.55 cm. Same for 2. 4.939 g + 3.822 g = 8.761 g However.. 17.8 + 12.11 The third 1 in 12.11 does not have a matching digit, because there is only one decimal place after 17.8. So, add. 17.8 + 12.11 = 29.91 And cross out the 1, to get 29.9 cm. Significant digit rules: 1- All numbers besides 0 are always significant. 2- Zeroes sandwiched betwene other numbers are significant. For example, 402, 3.04, 2.006. All of those zeroes are significant. 3- Zeroes at the end of a number without a decimal are NOT significant. 300- only the 3 is significant here. 3400- only the 3 and 4 are. 4- They are not significant before a number. 0534- the 0 is not. .009- the 2 zeroes act as placeholders and are not significant. 5- After a decimal at the end of a number, 0's are significant. 5.4400- both zeroes are significant. Following these rules: 1. 23- 2 sigfigs 2. 1.498- 4 sigfigs 3. 107- 3 sigfigs, the zero count because it is sandwiched 4. 0.05587 The zeroes do not count because they are placeholders. 4 sigfigs.