IB DP Chemistry Topic 11.1 Uncertainties and errors in measurement and results HL Paper 1

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.

N13/4/CHEMI/HPM/ENG/TZ0/40

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

A measuring cylinder was used to obtain a known volume of a liquid. The volume was read from the top of the meniscus and the liquid completely emptied into a flask. The exact same process was then repeated. Which statement is correct about the overall described procedure and the volumes measured?
 
A.  There is a systematic error and the volumes measured are accurate.
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%

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