Question
A student heated a solid in a crucible. The student measured the mass of the solid and crucible before and after heating and recorded the results.
\[\begin{array}{*{20}{l}} {{\text{Mass of crucible and solid before heating}}}&{ = 101.692{\text{ g}}} \\ {{\text{Mass of crucible and solid after heating}}}&{ = 89.312{\text{ g}}} \end{array}\]
What value should the student record for the mass lost in grams?
A. 12.4
B. 12.38
C. 12.380
D. 12.3800
▶️Answer/Explanation
C
mass lost in grams = 101.692 – 89.312 = 12.380 gm.
Question
A student measured the mass and volume of a piece of silver and recorded the following values.
Which value, in \({\text{g}}\,{\text{c}}{{\text{m}}^{ – 3}}\), for the density of silver should the student report in her laboratory notebook?
A. 10.49
B. 10.4900
C. 10.5
D. 10.500
▶️Answer/Explanation
C
Mass of silver = 11.5700-1.0800 = 10.4900 gm
Volume = 1.00 cm3
Density = M/V = 10.4900/1.00 gm/cm3= 10.5gm/cm3 (In 3 significant digits since volume had 3 significant digits).
Question
B. There is a random error and the volumes measured are accurate.
C. There is a random error and the volumes measured are inaccurate.
D. There is a systematic error and the volumes measured are inaccurate.
▶️Answer/Explanation
D
To measure the volume of liquid in a graduated cylinder, you should make a reading at the bottom of the meniscus, the lowest point on the curved surface of the liquid.
Here, volume was read from the top of the meniscus. Which is wrong and there is a systematic error and the volumes measured are inaccurate.
Question
The molar mass of a gas, determined experimentally, is 32 g mol−1. Its literature molar mass is 40 g mol−1.
What is the percentage error?
A. 80%
B. 25%
C. 20%
D. 8%
▶️Answer/Explanation
C
\(Percentage error =100\times \frac{(Literature molar mass – Experimental molar mass )}{Literature molar mass}\)
\(Percentage error =100\times \frac{(40 – 32 )}{40}\) = 20%