Chem 10 - Common Lab Measurements
If you are here, it is because you have already completed the measurements of Box 1 in your Chemistry 10 lab, Common Lab Measurements, and you want to check the accuracy and precision of your work against the correct answers. If you have not made these measurements, please do so before continuing. The point of this exercise is to give you feedback on how well you are doing your measurements so that you can do the measurements in the rest of the lab correctly, understanding where you made mistakes so you can learn from them!
If you have done the measurements and would like to check your work, you can click here to see the correct measurements for Box 1. In the space below, you can check your work for the "Information about the rulers" table.
dm ruler | cm ruler | mm ruler | |
value between marked divisions | 1 dm | 1 cm | 1 mm |
# of imagined divisions | 10 | 10 | 10 or 2 |
place value of last significant figure in your measurement | tenths | tenths | tenths |
number of digits after decimal to record for this ruler | 1 | 1 | 1 |
In each section below, we discuss the answers in the above table, and where they come
from.
Value between marked divisions
At first glance, the first row of this table might be a bit surprising. When you look at the cm ruler and the dm ruler, you can see that they are numbered "0", "1", "2", "3", and so on. The mm ruler is different, and is numbered "0", "10", "20", and so on. If they are numbered differently, shouldn't I put a different answer for "value between marked divisions?" And the answer is no, because the question asked about marked divisions, not numbered divisions. You can see this pictured in the mm ruler below:
In the centimeter ruler, there are no additional marks between the numbers, so the smallest marked divisions and smallest numbered divisions are both the same value of 1 cm. In the millimeter ruler, the smallest numbered division is shown on the bottom side of the ruler, and those are the "10" and "20" marks. So the distance between the smallest numbered division is 10 mm. Additionally, the millimeter ruler has 9 small marks in between the "10" and the "20", creating a total of 10 divisions in between those numbers. Each one of those divisions corresponds to 1 mm (try and count them if you want to check!), and that is what we are looking for in the value between marked divisions.
# of imagined divisions
Remember that the imagined divisions correspond to how many pieces you are breaking the empty space between the smallest marked divisions. For the centimeter ruler and decimeter ruler, this would be the space between the "1" and "2" numbers if that is where your measurement appears. For the millimeter ruler, this would be between two small marks, not between the "10" and "20". In many cases, it is very easy for our brains to break apart spaces into either 2 or 10 imagined divisions, with 10 being the most common. Your lab manual has more information on this. Since the decimeter and centimeter rulers are marked by 1 unit, and the spaces between the divisions is fairly large, they can easily be broken into 10 imaginary divisions. The millimeter ruler is a bit more difficult. A 1 mm spacing between marks can be hard to read or break into smaller divisions. If the marked lines are fairly fine, and the edge of what you are measuring is well defined, many people can successfully break that into 10 imaginary divisions. However, the box we are measuring has a wide edge width that makes it hard to measure exactly, and in some cases, some people might feel that they can only break the division into 2 imaginary divisions (the measurement is on the division / the measurement is between the division). So in this spot, either answer would be acceptable, as long as your measurements are consistent with what you write here.
Place value of last significant figure in your measurement
Since, in all cases, the smallest marked division was a unit of "1" (1 mm, 1 cm, 1 dm), the measuring device can always be read to the next digit to the right. The next digit to the right from the "ones" digit is the "tenths" digit.
Number of digits after decimal to record for this ruler
Since we are recording all measurements to the "tenths" digit, this corresponds to one digit after the decimal.