Question
Which observation would explain a systematic error for an experiment involving the combustion of magnesium to find the empirical formula of its oxide?
A. The crucible lid was slightly ajar during heating.
B. The product was a white powdery substance.
C. The crucible had black soot on the bottom after heating.
D. The flame colour during heating was yellow.
▶️Answer/Explanation
Markscheme: C
A systematic error is a consistent error that affects all measurements in the same way, typically resulting from a flaw in the experimental setup or procedure. Let’s analyze the given observations in the context of an experiment involving the combustion of magnesium to find the empirical formula of its oxide:
A. The crucible lid was slightly ajar during heating:
- This could lead to the escape of magnesium oxide vapors and affect the measurements. It suggests a potential systematic error as it is a consistent issue that could impact the results.
B. The product was a white powdery substance:
- This is more related to the nature of the product (magnesium oxide), and it doesn’t immediately suggest a systematic error. The color or form of the product may vary but doesn’t necessarily indicate a flaw in the experiment.
C. The crucible had black soot on the bottom after heating:
- This suggests incomplete combustion, and black soot may contain unburned carbon. This observation indicates a potential systematic error as it suggests that not all magnesium may have reacted to form magnesium oxide.
D. The flame color during heating was yellow:
- The color of the flame may be related to impurities or incomplete combustion. A yellow flame often indicates the presence of unburned carbon or other impurities. This could contribute to a systematic error if it consistently affects the combustion process.
Among the options, C. The crucible had black soot on the bottom after heating is more directly related to the combustion process and suggests a potential systematic error in the experiment. Incomplete combustion would lead to inaccurate results in determining the empirical formula of magnesium oxide.
Question
What is the mass, in g, of one molecule of ethane, \({{\text{C}}_{\text{2}}}{{\text{H}}_{\text{6}}}\)?
A. \(3.0 \times {10^{ – 23}}\)
B. \(5.0 \times {10^{ – 23}}\)
C. 30
D. \(1.8 \times {10^{25}}\)
Answer/Explanation
Markscheme
B
Examiners report
Question
A fixed mass of gas has a certain volume at a temperature of 50 °C. What temperature is required to double its volume while keeping the pressure constant?
A. 100 K
B. 323 K
C. 373 K
D. 646 K
Answer/Explanation
Markscheme
D
Examiners report
Question
What is the amount, in moles, of sulfate ions in \({\text{100 c}}{{\text{m}}^{\text{3}}}\) of \({\text{0.020 mol}}\,{\text{d}}{{\text{m}}^{ – 3}}{\text{ FeS}}{{\text{O}}_{\text{4}}}{\text{(aq)}}\)?
A. \(2.0 \times {10^{ – 3}}\)
B. \(2.0 \times {10^{ – 2}}\)
C. \(2.0 \times {10^{ – 1}}\)
D. 2.0
Answer/Explanation
Markscheme
A
Examiners report
Question
What volume, in \({{\text{m}}^{\text{3}}}\), is occupied by 2.00 mol of gas at 27 °C and 2.00 atm pressure?
Assume: \({\text{1.00 atm}} = 1.01 \times {10^5}{\text{ Pa}}\) and \(R = 8{\text{.}}31{\text{ J}}\,{{\text{K}}^{ – 1}}{\text{mo}}{{\text{l}}^{ – 1}}\).
A. \(\frac{{8.31 \times 27}}{{1.01 \times {{10}^5}}}\)
B. \(\frac{{2.00 \times 8.31 \times 27}}{{1.01 \times {{10}^5}}}\)
C. \(\frac{{2.00 \times 8.31 \times 300}}{{2.00 \times 1.01 \times {{10}^5}}}\)
D. \(\frac{{2.00 \times 8.31 \times 300}}{{1.01 \times {{10}^5}}}\)
Answer/Explanation
Markscheme
C