Moles And Molar Mass
A student weighs out 36.04 g of water (H₂O) on a laboratory balance. How many moles of water does this sample contain? (Molar mass of H₂O = 18.02 g mol⁻¹)
Which statement correctly describes why chemists use the mole as a counting unit?
Determine the number of molecules in 0.750 mol of carbon dioxide (CO₂).
The average mass of a single molecule of ammonia (NH₃) is 17.03 amu. A student claims that one molecule of ammonia therefore has a mass of 17.03 g. Which statement correctly identifies the error?
A chemist needs exactly 3.011 × 10²³ formula units of sodium chloride (NaCl). What mass of NaCl must be weighed out? (Molar mass of NaCl = 58.44 g mol⁻¹)
A student multiplies 25.0 g of iron (Fe) by 6.022 × 10²³ to find the number of atoms. What fundamental error has the student made?
Calculate the molar mass of glucose (C₆H₁₂O₆) given the following atomic masses: C = 12.01 amu, H = 1.008 amu, O = 16.00 amu.
A pharmaceutical company dissolves 90.08 g of glucose (C₆H₁₂O₆, M = 180.16 g mol⁻¹) in a saline drip. How many individual hydrogen atoms are present in this sample?
Equal masses (10.0 g each) of helium (He, M = 4.003 g mol⁻¹) and neon (Ne, M = 20.18 g mol⁻¹) are placed in separate sealed flasks. Which comparison of the two samples is correct?
An unknown pure element has a sample mass of 32.0 g that contains exactly 1.000 mol of atoms. What is the identity of this element?
A forensic chemist recovers a 5.85 g sample of a white powder confirmed to be pure NaCl from a crime scene. She needs to report the number of individual sodium ions (Na⁺) present. What is the correct value? (Molar mass of NaCl = 58.44 g mol⁻¹)
A student is given that one atom of element X has a mass of 63.55 amu. Without any further calculation, what can the student immediately state about element X?
A student calculates the number of atoms in 10.0 g of calcium (Ca, M = 40.08 g mol⁻¹) and obtains 1.50 × 10²⁴ atoms. Determine whether this answer is reasonable, and identify any error.
At high altitude, a mountaineer’s body produces additional red blood cells to compensate for lower oxygen availability. If the body synthesises 2.50 × 10⁻⁴ mol of haemoglobin (a protein), how many individual haemoglobin molecules does this represent?
Two beakers each contain exactly 1.00 mol of substance. Beaker 1 contains NaCl (an ionic compound) and Beaker 2 contains H₂O (a molecular compound). A student claims both beakers contain the same number of atoms. Evaluate this claim.
A sample contains 9.033 × 10²³ molecules of CH₄. What is the mass of this sample? (Molar mass of CH₄ = 16.04 g mol⁻¹)