Balancing Equations
_H₂ + _Cl₂ → __HCl
1 H₂ + 1 Cl₂ → 2HCl
- Balance elements on the reactant and product side ie H and Cl
Find the empirical formula for a compound containing 40% carbon, 6.7% hydrogen, and 53.3% oxygen by mass
Answer: CH₂O
Explanation: Divide each percentage by the atomic mass of the element to get the mole ratio:
C: 40/12.01 ≈ 3.33
H: 6.7/1.01 ≈ 6.63
O: 53.3/16 ≈ 3.33
Divide each value by the smallest value (3.33) to get the simplest whole-number ratio:
C: 3.33/3.33 = 1
H: 6.63/3.33 ≈ 2
O: 3.33/3.33 = 1
So, the empirical formula is CH₂O.
In the reaction 2H₂ + O₂ → 2H₂O, what is the mole ratio of hydrogen (H₂) to water (H₂O)?
Answer: 1:1
Explanation: The balanced equation shows that 2 moles of hydrogen react to produce 2 moles of water. Therefore, the mole ratio of H₂ to H₂O is 2:2, which simplifies to 1:1.
How many moles are in 25 grams of sodium chloride (NaCl)?
Answer: 0.43 moles
Explanation: First, find the molar mass of NaCl: NaCl = (1 x 22.99 g/mol of Na) + (1 x 35.45 g/mol of Cl) = 58.44 g/mol. Then, divide the mass (25 g) by the molar mass (58.44 g/mol): 25 g / 58.44 g/mol = 0.43 moles
What is the concentration of a solution made by dissolving 5 grams of sodium chloride (NaCl) in 500 milliliters of water?
Answer: 0.171 M
Explanation: First, find the molar mass of NaCl: NaCl = (1 x 22.99 g/mol of Na) + (1 x 35.45 g/mol of Cl) = 58.44 g/mol. Then, convert the mass to moles: 5 g / 58.44 g/mol = 0.0854 moles. Next, convert the volume to liters: 500 mL x (1 L/1000 mL) = 0.5 L. Finally, divide the number of moles by the volume in liters to get the concentration: 0.0854 moles / 0.5 L = 0.171 M.
_H₂O₂ → _H₂O + O₂
2H₂O₂ → 2H₂O + O₂
Find the empirical formula for a compound containing 43.64% phosphorus and 56.36% oxygen by mass
Answer: P₂O₅
Explanation: Divide each percentage by the atomic mass of the element to get the mole ratio:
P: 43.64/30.97 ≈ 1.41
O: 56.36/16 ≈ 3.52
Divide each value by the smallest value (1.41) to get the simplest whole-number ratio:
P: 1.41/1.41 = 1
O: 3.52/1.41 ≈ 2.5
Since we need whole numbers, multiply each value by 2:
P: 1 x 2 = 2
O: 2.5 x 2 = 5
So, the empirical formula is P₂O₅
How many moles are in 100 grams of water (H₂O)?
Answer: 5.56 moles
Explanation: First, find the molar mass of water: H₂O = (2 x 1.01 g/mol of H) + (1 x 16.00 g/mol of O) = 18.02 g/mol. Then, divide the mass (100 g) by the molar mass (18.02 g/mol): 100 g / 18.02 g/mol = 5.56 moles
How many atoms are in 3 moles of carbon (C)?
Answer: 1.81 x 10^24 atoms
Explanation: One mole of carbon contains 6.02 x 10^23 atoms (Avogadro's number). Therefore, 3 moles of carbon contain 3 x 6.02 x 10^23 atoms = 1.81 x 10^24 atoms
If 10 grams of reactant A produces 8 grams of product B in a reaction, what is the percentage yield?
Answer: 80%
Explanation: Percentage yield is calculated by dividing the actual yield (8 grams) by the theoretical yield (10 grams) and multiplying by 100. So, (8 g / 10 g) x 100 = 80%
__Al + __CuCl₂ → __AlCl₃ + __Cu
2Al + 3CuCl₂ → 2AlCl₃ + 3Cu
Find the molecular formula for a compound with the empirical formula CH₂O and a molecular weight of 180 g/mol.
Answer: C₆H₁₂O₆
Explanation: The empirical formula mass of CH₂O is approximately 30 g/mol (12.01 + 2.01 + 16.00). Divide the molecular weight by the empirical formula mass to get the empirical formula multiplier:
180 g/mol ÷ 30 g/mol = 6
Multiply the subscripts in the empirical formula by the multiplier to get the molecular formula:
C: 1 x 6 = 6
H: 2 x 6 = 12
O: 1 x 6 = 6
So, the molecular formula is C₆H₁₂O₆.
How many moles are in 40 grams of calcium (Ca)?
Answer: 1 mole
Explanation: The molar mass of calcium is 40.08 g/mol. Divide the mass (40 g) by the molar mass (40.08 g/mol): 40 g / 40.08 g/mol = 1 mole
How many moles are in 100 milligrams of magnesium (Mg)?
Answer: 4.10 x 10^-3 moles
Explanation: The molar mass of magnesium is 24.31 g/mol. First, convert the mass to grams: 100 mg x (1 g/1000 mg) = 0.1 g. Then, divide the mass (0.1 g) by the molar mass (24.31 g/mol): 0.1 g / 24.31 g/mol = 4.10 x 10^-3 moles
How many grams of sodium hydroxide (NaOH) are needed to make 1 liter of a 0.5 M solution?
Answer: 20 g
Explanation: First, find the molar mass of NaOH: NaOH = (1 x 22.99 g/mol of Na) + (1 x 16.00 g/mol of O) + (1 x 1.01 g/mol of H) = 40.00 g/mol. Then, multiply the desired concentration by the desired volume in liters to get the number of moles: 0.5 M x 1 L = 0.5 moles. Finally, multiply the number of moles by the molar mass to get the mass in grams: 0.5 moles x 40.00 g/mol = 20 g
C₃H₈ + __O₂ → __CO₂ + __H₂O
C₃H₈ + 5O₂ → 3CO₂ + 4H₂O
Find the molecular formula for a compound with the empirical formula CH and a molecular weight of 78 g/mol.
Answer: C₆H₆
Explanation: The empirical formula mass of CH is approximately 13 g/mol (12.01 + 1.01). Divide the molecular weight by the empirical formula mass to get the empirical formula multiplier:
78 g/mol ÷ 13 g/mol = 6
Multiply the subscripts in the empirical formula by the multiplier to get the molecular formula:
C: 1 x 6 = 6
H: 1 x 6 = 6
So, the molecular formula is C₆H₆.
In the reaction N₂ + 3H₂ → 2NH₃, what is the mole ratio of nitrogen (N₂) to ammonia (NH₃)?
Answer: 1:2
Explanation: The balanced equation shows that 1 mole of nitrogen reacts with 3 moles of hydrogen to produce 2 moles of ammonia. Therefore, the mole ratio of N₂ to NH₃ is 1:2.
How many molecules are in 2.5 grams of water (H₂O)?
Answer: 4.16 x 10^22 molecules
Explanation: The molar mass of water is 18.02 g/mol. First, convert the mass to moles: 2.5 g / 18.02 g/mol = 0.139 moles. Then, multiply the number of moles by Avogadro's number (6.02 x 10^23 molecules/mol) to get the number of molecules: 0.139 moles x 6.02 x 10^23 molecules/mol = 4.16 x 10^22 molecules
A chemist expects to obtain 25 grams of product D from a reaction, but only gets 18 grams. What is the percentage yield?
Answer: 72%
Explanation: Percentage yield is calculated by dividing the actual yield (18 grams) by the theoretical yield (25 grams) and multiplying by 100. So, (18 g / 25 g) x 100 = 72%
__KClO₃ → __KCl + __O₂
2KClO₃ → 2KCl + 3O₂
Find the empirical formula for a compound containing 0.15 g of nitrogen, 0.30 g of sulfur, and 0.45 g of oxygen
Answer: N₂SO₃
Explanation: Convert grams to moles for each element:
N: 0.15/14.01 ≈ 0.0107
S: 0.30/32.07 ≈ 0.00936
O: 0.45/16 ≈ 0.0281
Divide each value by the smallest value (0.00936) to get the simplest whole-number ratio:
N: 0.0107/0.00936
How many grams of carbon dioxide (CO2) are produced from 2 moles of methane (CH4) in a combustion reaction?
Answer: 88 grams
Explanation: The balanced chemical equation for the combustion of methane is CH4 + 2O2 -> CO2 + 2H2O.
This tells us that for every 1 mole of methane, 1 mole of carbon dioxide is produced. Therefore, 2 moles of methane will produce 2 moles of carbon dioxide. The molar mass of CO2 is 44 grams/mole, so 2 moles of CO2 will have a mass of 88 grams (2 moles x 44 grams/mole)
How many moles are in 1.5 x 10^24 atoms of carbon (C)?
Answer: 2.49 x 10^8 moles
Explanation: First, find the molar mass of carbon: 12.01 g/mol. Then, divide the number of atoms by Avogadro's number (6.02 x 10^23 atoms/mol) to get the number of moles: 1.5 x 10^24 atoms / 6.02 x 10^23 atoms/mol = 2.49 x 10^8 moles
In a reaction, the theoretical yield of product C is 15 grams, but only 12 grams are obtained experimentally. What is the percentage yield?
Answer: 80%
Explanation: Percentage yield is calculated by dividing the actual yield (12 grams) by the theoretical yield (15 grams) and multiplying by 100. So, (12 g / 15 g) x 100 = 80%