Regents Chemistry Exam August 2024 Question 47
47 A sample of LiOH(aq) has a concentration of 0.020 M. How many significant figures are used to express the concentration of this solution?
(1) 1 (3) 3
(2) 2 (4) 4
Solution:
Let's go over the rules for significant figures:
All non-zero digits are significant. This means all numbers: 1,2,3,4,5,6,7,8, and 9 are significant. For example 5.67 has 3 significant figures.
All zeroes in between non-zero numbers are significant. For example zero in 303 is significant.
Leading zeroes (zeroes to the left of a number) are not significant. For example: 0.0009 has only one significant figure (9) since all of the zeroes to the left of it are not significant.
Trailing zeros to the right of a decimal point are significant. For example zeroes in 3.400 are significant.
In 0.020, the first two zeroes are not significant (leading zeroes), while 2 and 0 after 2 are significant. There are 2 significant figures in this number.
Choice 2 is the correct answer.
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