HESI A2 Chemistry Stoichiometry

Find out how many moles are water (𝐻2𝑂) are produced when 4 moles of hydrogen gas (𝐻2) react with excess oxygen gas (𝑂2) according to the balance chemical equations: 2𝐻2+𝑂2→2𝐻2𝑂

4 moles H2O are produced (the ratio is 2:2)

if 7.0 moles of 𝑃2𝑂5 were produced, how many moles of 𝑃 would be required in this chemical equation: 4𝑃(𝑠)+5𝑂2(𝑔)→2𝑃2𝑂5(𝑠)

14 moles P are produced (the ratio is 2:1)

What is the mole ratio of hydrogen to oxygen in the reaction 2H2+O2→2H2O?

1:1

2:1

2:2

1:2

2:1

Given the reaction N2+3H2→2NH3​, what is the mole ratio of nitrogen to ammonia?

2:3

1:2

2:1

1:3

1:2

How many moles of O2​ are needed to react with 2 moles of C2H6 in the reaction 2C2H6+7O2→4CO2+6H2O?

14 moles

2 moles

3.5 moles

7 moles

7 moles

In the reaction 3H2+N2→2NH3​, how many moles of H2 are needed to produce 6 moles of NH3?

12 moles

6 moles

9 moles

3 moles

9 moles

How many moles of oxygen are needed to react with 0.5 moles of C3H8​ in the reaction C3H8+5O2→3CO2+4H2O?

0.5 moles

1.5 moles

2.5 moles

5 moles

2.5 moles (the ratio is 1:5)

How many moles of NH3 can be produced from 1.5 moles of N2​ in the reaction N2+3H2→2NH3?

2 moles

1.5 moles

1 mole

3 moles

3 moles

Given the reaction 4FeS2+11O2→2Fe2O3+8SO2​, what is the mole ratio of FeS2​ to SO2​?

1:2

8:4

1:1

2:3

1:2

What is the percent concentration of a solution with 5 grams of sugar dissolved in 95 grams of water?

4%

5%

10%

20%

5%

What is the percent concentration of 10 grams of salt in 90 grams of water?

8%

10%

11%

12%

10%

How many grams of solute are in a 15% solution with a total mass of 200 g?

15g

20g

30g

35g

30g (200 x 0.15)

What is the percent concentration of a solution with 8 grams of solute in 192 grams of solvent?

4%

8%

12%

15%

4% (8/200= 0.04(100) = 4%)

What is the molarity of a solution with 2 grams of NaCl dissolved in 500 mL of water?(Molar mass of NaCl=58.5g/mol)

0.034 M

0.068 M

0.1 M

0.2 M

0.068 M

How many moles are in 1.5 L of a 2 M NaCl solution?

1.5 mol

2 mol

3 mol

mol

3 mol *M means moles per liter, multiply 2 M by 1.5 L

What is the molarity if 10 g of LiNO3 is dissolved in 250 mL of water?(Molar mass=69g/mol)

0.25 M

0.35 M

0.58 M

0.75 M

0.58 M

How many moles of solute are in 4 L of a 0.75 M solution?

1 mol

2 mol

3 mol

4 mol

3 mol

What is the molarity of a solution containing 5 g of NaOH in 1 L of water?(Molar mass=40g/mol)

0.125 M

0.5 M

1 M

5 M

0.125 M

The mass of a grain of sand is 1.672 × 10-4 kg. Express this number in standard notation.

0.0001672 kg

0.00001672 kg

1,672,000 kg

1,672 kg

0.0001672 kg

What is 6,987,000 in scientific notation?

6.987 x 105

69.87 x 105

6.987 x 106

0.6987 x 107

6.987 x 106

What is the molar mass of calcium phosphate, Ca₃(PO₄)₂?

A. 279.87 g/mol

B. 310.18 g/mol

C. 262.86 g/mol

D. 194.18 g/mol

Ca = 40.08 × 3 = 120.24

P = 30.97 × 2 = 61.94

O = 16.00 × 8 = 128.00

Total = 120.24 + 61.94 + 128.00 = 310.18 g/mol

✅ Correct Answer: B. 310.18 g/mol

How many moles are in 88.0 grams of carbon dioxide (CO₂)?

A. 2.00 mol

B. 1.50 mol

C. 3.00 mol

D. 4.00 mol

Molar mass of CO₂ = 12.01 + (16.00 × 2) = 44.01 g/mol

Moles = Mass / Molar Mass = 88.0 g / 44.01 g/mol ≈ 2.00 mol

✅ Correct Answer: A. 2.00 mol

What is the molar mass of aluminum sulfate, Al₂(SO₄)₃?

A. 150.14 g/mol

B. 342.15 g/mol

C. 294.18 g/mol

D. 278.20 g/mol

Al = 26.98 × 2 = 53.96

S = 32.07 × 3 = 96.21

O = 16.00 × 12 = 192.00

Total = 53.96 + 96.21 + 192.00 = 342.17 g/mol (rounding)

✅ Correct Answer: B. 342.15 g/mol

What is the mass of 0.75 moles of sodium chloride (NaCl)?

A. 43.83 g

B. 58.44 g

C. 29.22 g

D. 69.21 g

Molar mass of NaCl = 22.99 + 35.45 = 58.44 g/mol

Mass = Moles × Molar Mass = 0.75 mol × 58.44 g/mol = 43.83 g

✅ Correct Answer: A. 43.83 g

How many grams of carbon dioxide are produced when 32 g of methane (CH₄) are burned in excess oxygen?

CH4​+2O2 ---> CO2​+2H2​O

Molar mass of CH₄ = 16.04 g/mol

Molar mass of CO₂ = 44.01 g/mol

A. 22.0 g

B. 44.0 g

C. 88.0 g

D. 16.0 g

Convert mass of CH₄ to moles:

32 g ÷ 16.04 g/mol ≈ 2 mol

Use mole ratio:

1 mol CH₄ : 1 mol CO₂

so 2 mol CH₄ → 2 mol CO₂

Convert moles of CO₂ to grams:

2 mol × 44.01 g/mol= 88.02 g

✅ Correct Answer: C. 88.0 g

Given the reaction

2Al + 3Cl2→2AlCl3

​If you have 5.0 mol of Al and 6.0 mol of Cl₂, what is the limiting reactant?

A. Al

B. Cl₂

C. AlCl₃

D. Neither

Need 3 mol Cl₂ for every 2 mol Al

Only have 6 mol Cl₂ → Cl₂ is limiting (falling short of amount needed for reaction/running out first)

B. Cl₂

How many grams of water are produced when 3 moles of oxygen react with hydrogen gas?

Equation: 2H2+O2→2H2O2

Molar mass of H₂O = 18.02 g/mol

A. 18.02 g

B. 36.04 g

C. 54.06 g

D. 108.12 g

1 mol O₂ → 2 mol H₂O

So 3 mol O₂ → 6 mol H₂O

6 mol × 18.02 g/mol = 108.12 g

✅ Correct Answer: D. 108.12 g

Balance the following chemical equation:

__Al+__O2→__Al2O3

What are the correct coefficients (in lowest whole numbers) to balance the equation?

A. 2, 1, 1

B. 4, 3, 2

C. 2, 3, 2

D. 1, 1, 1

B. 4, 3, 2

Balance the following chemical equation:

__C3H8+__O2→__CO2+__H2​O

What are the correct coefficients (in lowest whole numbers)?

A. 1, 4, 3, 4

B. 2, 7, 6, 8

C. 1, 5, 3, 4

D. 1, 3, 3, 3

C. 1, 5, 3, 4

Molarity formula

M = mol solute/L solution

molar mass

(g/mol) sum of atomic mass of all atoms in a compound

moles formula

mass (g)/molar mass (g/mol)