Atomic Structure And Properties All subtopics
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)
In the mass spectrum of an element, what does the height of a peak represent?
A mass spectrum of an element displays peaks at m/z = 24, 25, and 26. How many naturally occurring isotopes does this element have?
Gallium has two stable isotopes: ⁶⁹Ga with a mass of 68.93 amu and 60.11% abundance, and ⁷¹Ga with a mass of 70.92 amu and 39.89% abundance. Calculate the average atomic mass of gallium.
An element has two isotopes with masses of 107 amu and 109 amu. The mass spectrum shows the peak at 107 is roughly equal in height to the peak at 109, but very slightly taller. Which value best estimates the average atomic mass?