A sample of magnesium weighs 12.0 g. Magnesium reacts with oxygen to form magnesium oxide (MgO).
i) Write the formula for calculating mass using moles and molar mass.
ii) Calculate the number of moles of magnesium in the sample.
Using the mole ratio, determine the number of moles of MgO formed.
Calculate the mass of MgO produced. (Molar masses: Mg = 24.30 g/mol, MgO = 40.30 g/mol)
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A container holds 4.5 g of water (H2O).
Calculate the number of moles of water in the container.
Calculate the total number of water molecules in the sample (Avogadro’s number = 6.022 × 1023).
Determine the total number of hydrogen atoms in the sample.
Determine the ratio of oxygen atoms to hydrogen atoms in the sample.
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A sample of a hydrated salt, MgSO4⋅xH2O, is heated to remove all the water of crystallization, leaving an anhydrous salt.
Mass of hydrated salt: 4.93 g
Mass of anhydrous MgSO4: 2.41g
Calculate the mass of water lost during heating.
Calculate the number of moles of water lost.
Determine the number of water molecules (x) in the formula of the hydrated salt.
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A student analyzes a sample of a white solid known to be a Group 1 metal carbonate with the general formula M2CO3, where M represents a Group 1 metal. A 0.622 g sample is placed in a test tube and heated strongly. A gas is produced, which is bubbled through limewater, Ca(OH)2 (aq), causing the limewater to turn cloudy. After heating is complete, the remaining solid has a mass of 0.424 g.
Write the balanced chemical equation for the thermal decomposition of M2CO3 (s).
Write the balanced chemical equation for the reaction that causes the limewater to turn cloudy.
Suggest one observable piece of evidence, other than the change in limewater, that could indicate that a chemical change occurred during the heating.
Use the given masses to calculate the number of moles of gas produced.
Use your answer to part (d) and the balanced equation from part (a) to calculate the molar mass of the unknown carbonate.
Use your answer to part (e) to identify the Group 1 metal (M). Justify your answer.
A student repeats the experiment but accidentally spills some of the solid before weighing it after heating.
Explain whether the calculated molar mass of M2CO3 would be too high, too low, or unchanged?
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A reaction occurs between aluminum and chlorine gas to form aluminum chloride (AlCl3):
2Al + 3Cl2 → 2AlCl3
Calculate the number of moles in a 4.92 g sample of aluminum.
If 19.08 g of chlorine gas (Cl2) is used, determine the limiting reactant. Justify your answer.
Calculate the maximum mass of AlCl3 produced. (Molar mass: AlCl3 = 133.30 g/mol)
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A 50.0 g sample of a compound contains 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen by mass.
Calculate the number of moles of each element in the sample.
Determine the simplest whole-number ratio of the elements and state the empirical formula of the compound.
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A student investigates a rectangular sheet of copper to estimate the size of a copper atom.
The rectangular sheet of copper has a mass of 2.54 g. Calculate the number of atoms in the sheet.
The sheet has dimensions 10.0 cm × 5.00 cm and a thickness of 5.0 × 10-3 cm. The density of copper is 8.96 g/cm3.
i) Calculate the volume of the copper sheet, in cm3.
ii) Use your answers from parts (a) and (b)(i) to determine the number of copper atoms per cubic centimeter.
The student models copper atoms as cubes packed in a simple cubic arrangement.
i) Assuming each copper atom occupies an equal volume in the sheet, calculate the volume, in cm3, occupied by a single atom.
ii) Use your answer from part (c)(i) to estimate the length of the cube occupied by one copper atom. Express your answer in picometers (pm).
(1 cm = 1010 pm)
The accepted atomic radius of copper is 128 pm.
Explain whether the estimate from part (c)(ii) supports the accepted atomic radius of copper? Use a claim–evidence–reasoning structure in your answer.
A simplified representation of part of the copper sheet is shown below. Each sphere represents one atom of copper in a square grid arrangement.
i) Identify one assumption the student is making by modeling the copper sheet with this atomic arrangement.
ii) Explain how this assumption might affect the accuracy of the estimated atomic size compared to the actual atomic radius.
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A student is tasked with preparing a solution containing 0.5 moles of sodium chloride (NaCl).
Calculate the mass of sodium chloride required.
If the student uses 35.0 g of sodium chloride, calculate the molarity of the solution if the final volume is 500.0 mL.
Suggest one way the student could correct the solution in part (b) to meet the original molarity target.
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