moles, particles & Avogadro's constant
What is 6.02 × 10²³ particles per mole?
This number represents Avogadro’s constant, the number of particles in one mole.
Calculate the molar mass of H₂O
18.02g/mol
This is the formula used to calculate percentage yield.
Percentage yield = actual yield / theoretical yield x100
I am in abundance in a reaction. What am I?
Excess reactant
maximum number of electrons in the p orbital
6
How many particles are present in 0.50 mol of helium atoms?
3.01×1023 helium atoms
Calculate the number of moles in 36.0 g of H₂O
2.00 mol
A reaction has a theoretical yield of 20.0 g and an actual yield of 15.0 g. Calculate the percentage yield.
75%
In the reaction 2H2+O2→2H2O, if you have 4 mol H₂ and 3 mol O₂, identify the limiting reactant.
Hydrogen
Write the full electron configuration for oxygen (O), which has 8 electrons
1s2, 2s2, 2p4
A sample contains 1.806 × 10²⁴ molecules of water (H₂O). How many moles is this?
3.00 mol
Calculate the mass of 2.50 mol of CO₂
110g
A reaction produces 42 g of product when the theoretical yield is 50 g. Calculate the percentage yield.
84%
In N2+3H2→2NH3, 2.0 mol N₂ reacts with 4.0 mol H₂. Identify the limiting reactant.
Hydrogen is limiting
Write the condensed electron configuration for calcium (Ca), which has 20 electrons.
How many oxygen molecules (O₂) are present in 3.50 mol of oxygen gas?
2.11×1024 oxygen molecules
A sample contains 0.750 mol of NaCl. Calculate its mass.
43.9g
A reaction has a 75% yield and a theoretical yield of 80 g. Calculate the actual yield.
60g
In 2Mg+O2→2MgO, 5.0 mol Mg reacts with 2.0 mol O₂. Identify the limiting reactant and calculate the maximum moles of MgO produced
Oxygen is limiting; 4.0mol MgO
An atom has the electron configuration 1s² 2s² 2p⁶ 3s² 3p⁵. Identify the element and state how many valence electrons it has.
Chlorine; 7 valence electrons
A sample contains 4.515 × 10²³ atoms of magnesium. Calculate the number of moles present and then determine the mass of magnesium.
0.75 mol and 18.2 g of magnesium
A sample contains 3.55g of CO2, calculate the number of particles in the sample.
4.816 x 1022 particles
Magnesium reacts with hydrochloric acid according to the equation:
Mg+2HCl→MgCl2+H2
A student reacts 12.0 g of Mg with excess HCl. They collect 9.50 g of MgCl₂.
Calculate the percentage yield of MgCl₂.
20.2%
In 2Al+3Cl2→2AlCl3, 10.0 g Al reacts with 25.0 g Cl₂. Determine the limiting reactant and calculate the theoretical mass of AlCl₃ produced
Limiting reactant: Cl₂
Theoretical yield: 31.4 g AlCl₃
Chromium has 24 electrons. Its expected configuration is [Ar] 4s² 3d⁴, but its actual configuration is [Ar] 4s¹ 3d⁵. Explain why chromium is an exception to the expected filling pattern.
The d⁵ arrangement is particularly stable because the five d orbitals are half-filled, so one 4s electron moves into the 3d subshell.