Question

1. For the reaction C + 2H2 → CH4, how many moles of carbon are needed to make 150.6 grams of methane, CH4 ?

Round your answer to the nearest tenth. If you answer is a whole number like 4, report the answer as 4.0

Use the following molar masses. If you do not use these masses, the computer will mark your answer incorrect.:

Element

Molar Mass

Hydrogen

1

Carbon

12


2. S + 6 HNO3 --> H2SO4 + 6 NO2 + 2 H2O

In the above equation how many moles of water can be made when 113 grams of HNO3 are consumed?

Round your answer to the nearest tenth. If you answer is a whole number like 4, report the answer as 4.0

Use the following molar masses. If you do not use these masses, the computer will mark your answer incorrect.:

Element

Molar Mass

Hydrogen

1

Nitrogen

14

Sulfur

32

Oxygen

16


3. 3 Cu + 8HNO3 --> 3 Cu(NO3)2 + 2 NO + 4 H2O

In the above equation how many moles of water can be made when 117.8 grams of HNO3 are consumed?

Round your answer to the nearest tenth. If you answer is a whole number like 4, report the answer as 4.0

Use the following molar masses. If you do not use these masses, the computer will mark your answer incorrect.:

Element

Molar Mass

Hydrogen

1

Nitrogen

14

Copper

63.5

Oxygen

16

Answer 1

1) 9.4 mol

2) 0.6 mol

3) 0.9 mol

What is Stoichiometry?

In chemical equations, unless stated otherwise, the reactants and products will theoretically always remain in stoichiometric ratios.

The stoichiometry of a reaction is the relationship between the relative quantities of products and reactants, typically a ratio of whole integers.

Consider the following chemical reaction: aA + bB ⇒ cC + dD.

The stoichiometry of reactants to products in this reaction is the ratio of the coefficients of each species: a : b : c : d.

Converting between moles and mass:

To convert from mass to moles, divide the mass present by the molar mass, resulting in the number of moles. Mathematically, the units present themselves like this:
`(g)/(gmol^(-1)) =g(g^(-1)mol)=mol`.

Thence, the formula for moles: n = m/M, where n = number of moles, m = mass present, and M = molar mass. This formula can be easily rearranged to find mass present from molar mass and moles, or molar mass from mass and moles.

1) For the reaction C + 2H₂ → CH₄, how many moles of carbon are needed to make 150.6 g of methane, CH₄? (Molar Masses: H=1; C=12)

Stoichiometry of carbon to methane = 1 : 1.

Therefore, moles of CH₄ = moles of C. Using the formula to find moles, n(CH₄) = m/M = 150.6/(12+1×4) =9.4125 ≈ 9.4 mol

Therefore, we require 9.4 moles of carbon.

2) S + 6HNO₃ → H₂SO₄ + 6NO₂ + 2H₂O

In the above equation, how many moles of water can be made when 113 g of HNO₃ are consumed? (Molar Masses: H=1; N=14; S=32; O=16)

Stoichiometry of Nitric acid to water = 6 : 2 = 3 : 1. Therefore, we produce 1 mole of water for every 3 moles of nitric acid consumed. Hence, n(HNO₃) = m/M = 113/(1+14+16×3) = 1.79365 mol

Therefore: n(H₂O) = 1/3 × n(HNO₃) = 0.59788 mol ≈ 0.6 mol

3) 3Cu + 8HNO₃ → 3Cu(NO₃)₂ + 2NO + 4H₂O

In the above equation, how many moles of water can be made when 117.8 grams of HNO3 are consumed?

Stoichiometry of Nitric acid to water = 8 : 4 = 2 : 1. Therefore, we produce 1 mole of water for every 2 moles of nitric acid consumed. Hence, n(HNO₃) = m/M = 117.8/(1+14+16×3) = 1.86984 mol

Therefore: n(H₂O) = 1/2 × n(HNO₃) = 0.9349 mol ≈ 0.9 mol