2023-May-Chemistry_paper_1__TZ1_SL
Topic:Physical constants and unit conversions .
Calculate:the units of molar mass?
A. amu
B. g
C. mol \(g^{-1}\)
D. g \(mol^{-1}\)
▶️Answer/Explanation
Markscheme: D
Molar mass is the mass of one mole of a substance and is expressed in grams per mole (g/mol). Therefore, the correct units for molar mass are represented as g/mol. This unit indicates the amount of mass in grams contained in one mole of a given substance.
In the International System of Units (SI), the mole is the base unit for amount of substance, and grams are the base unit for mass. Combining these two units gives the molar mass in grams per mole.
2023-May-Chemistry_paper_1__TZ1_SL
Topic: The mole concept
Discuss: information does the molecular formula provide?
A. The simplest ratio of atoms in a molecule
B. The actual numbers of atoms in a molecule
C. The number of molecules in one mole
D. The types of bonds in a molecule
▶️Answer/Explanation
Markscheme : B
A molecule is comprised of two or more atoms that have been chemically combined. A molecular formula is a chemical formula of a molecular compound that shows the kinds and numbers of atoms present in a molecule of the compound.
2023-May-Chemistry_paper_1__TZ1_SL
Topic: The mole concept
Given : A student heated a known mass of zinc powder in an open crucible until there was no further mass change and recorded the final mass.
Discuss: What would the student be able to derive from this data?
I. Percentage composition of zinc oxide
II. Empirical formula of zinc oxide
III. Molecular formula of zinc oxide
A. I and II only
B. I and III only
C. II and III only
D. I, II and III
▶️Answer/Explanation
Markscheme: A
The student would be able to derive the following information:
I. Percentage composition of zinc oxide – Yes, by comparing the initial and final masses, the student can determine the percentage of zinc in the zinc oxide formed.
II. Empirical formula of zinc oxide – Yes, by determining the moles of zinc and oxygen involved in the reaction, the student can find the empirical formula.
III. Molecular formula of zinc oxide – No, the molecular formula cannot be determined from this experiment alone. To find the molecular formula, additional information about the molar mass of the compound is needed.
Therefore, the correct answer is A. I and II only.
2023-May-Chemistry_paper_1__TZ1_SL
Topic:Gas Laws
Calculate: molar mass of a gas according to the following experimental data?
Ideal gas constant = 8.31 \(JK^{-1} mol^{-1}\)
A. \(\frac{40.0 \times 8.31 \times 290}{98 \times 0.220}\)
B. \(\frac{98 \times 0.220}{40.0 \times 8.31 \times 290}\)
C. \(\frac{40.0 \times 8.31 \times 17}{98 \times 0.220}\)
D. \(\frac{98 \times 220}{40.0 \times 8.31 \times 17}\)
▶️Answer/Explanation
Markscheme: A
To find the molar mass of the gas, you can rearrange the ideal gas law equation \(\mathrm{PV}=\mathrm{nRT}\) to solve for the number of moles (\(\mathrm{n}\)) and then use the formula for molar mass (\(\mathrm{M}\)):
\[\mathrm{Molar\ mass} (\mathrm{M}) = \frac{\text{Mass of gas}}{\text{Number of moles}}\]
First, find the number of moles using the ideal gas law:
\[\mathrm{n} = \frac{\mathrm{PV}}{\mathrm{RT}}\]
Now, substitute the given values:
\[\mathrm{n} = \frac{(98 \, \mathrm{kPa}) \times (0.220 \, \mathrm{L})}{(8.31 \, \mathrm{J} \, \mathrm{K}^{-1} \, \mathrm{mol}^{-1}) \times (290 \, \mathrm{K})}\]
Now, substitute the value of \(\mathrm{n}\) into the formula for molar mass:
\[\mathrm{M} = \frac{\text{Mass of gas}}{\text{Number of moles}} = \frac{40.0 \, \mathrm{g}}{\mathrm{n}}\]
so, \[\mathrm{M} =\frac{40.0 \times 8.31 \times 290}{98 \times 0.220}\]