HNO3, H2SO4 & HCl Calculations: Grams From Reactions

Oct 19, 2025 by SLV Team 53 views

Hey guys! Today, we're diving into some stoichiometry problems to figure out how many grams of certain acids we can get from different reactions. We'll be tackling three questions focusing on nitric acid (HNO3), sulfuric acid (H2SO4), and hydrochloric acid (HCl). So, grab your calculators, and let's get started!

Question 25: Calculating HNO3 Yield from NH3

How many grams of HNO3 can be obtained from 34 g of NH3?

This is a classic stoichiometry problem, and to solve it, we need to follow a few key steps. First, we'll need to look at the balanced chemical equation for the reaction that produces nitric acid (HNO3) from ammonia (NH3). Although the question doesn't give us the full reaction, it implies the industrial process for nitric acid production, which involves several steps. However, the key relationship we need to focus on is the conversion of NH3 to HNO3. We will consider a simplified version of the reaction for this calculation. A common method involves the Ostwald process, but for simplicity, let’s consider a conceptual reaction where NH3 directly converts to HNO3:

NH3 + some oxidants → HNO3 + other products

Step 1: Convert grams of NH3 to moles of NH3

To do this, we'll need the molar mass of NH3 (ammonia). The molar mass of nitrogen (N) is approximately 14 g/mol, and the molar mass of hydrogen (H) is approximately 1 g/mol. So, the molar mass of NH3 is 14 + (3 * 1) = 17 g/mol.

Now, we can convert 34 g of NH3 to moles:

Moles of NH3 = (grams of NH3) / (molar mass of NH3) Moles of NH3 = 34 g / 17 g/mol = 2 moles

So, we have 2 moles of NH3.

Step 2: Use the Stoichiometric Ratio to Find Moles of HNO3

From the conceptual balanced equation (NH3 → HNO3), the stoichiometric ratio between NH3 and HNO3 is 1:1. This means that for every 1 mole of NH3, we can produce 1 mole of HNO3. Therefore, if we start with 2 moles of NH3, we can theoretically produce 2 moles of HNO3.

Step 3: Convert Moles of HNO3 to Grams of HNO3

To do this, we need the molar mass of HNO3 (nitric acid). The molar mass of hydrogen (H) is approximately 1 g/mol, the molar mass of nitrogen (N) is approximately 14 g/mol, and the molar mass of oxygen (O) is approximately 16 g/mol. So, the molar mass of HNO3 is 1 + 14 + (3 * 16) = 63 g/mol.

Now, we can convert 2 moles of HNO3 to grams:

Grams of HNO3 = (moles of HNO3) * (molar mass of HNO3) Grams of HNO3 = 2 moles * 63 g/mol = 126 g

Therefore, we can obtain 126 grams of HNO3 from 34 g of NH3. So the correct answer is B) 126.

Question 26: Calculating H2SO4 Yield from FeS2

How many grams of H2SO4 can be obtained from 40 g of FeS2?

Alright, let's tackle another stoichiometry problem, this time involving sulfuric acid (H2SO4) and iron pyrite (FeS2). This one’s a bit more complex, as it involves a multi-step process. The industrial production of sulfuric acid from FeS2 involves several reactions, including the oxidation of FeS2 to SO2, the oxidation of SO2 to SO3, and finally the reaction of SO3 with water to form H2SO4. For simplicity, we'll focus on the overall stoichiometry:

FeS2 → 2 SO2 → 2 SO3 → 2 H2SO4

This simplified view helps us understand the molar relationships. We’ll consider the key steps involved to convert FeS2 to H2SO4.

Step 1: Convert grams of FeS2 to moles of FeS2

First, we need to calculate the molar mass of FeS2 (iron pyrite). The molar mass of iron (Fe) is approximately 56 g/mol, and the molar mass of sulfur (S) is approximately 32 g/mol. So, the molar mass of FeS2 is 56 + (2 * 32) = 56 + 64 = 120 g/mol.

Now, we convert 40 g of FeS2 to moles:

Moles of FeS2 = (grams of FeS2) / (molar mass of FeS2) Moles of FeS2 = 40 g / 120 g/mol = 1/3 moles ≈ 0.333 moles

So, we have approximately 0.333 moles of FeS2.

Step 2: Use the Stoichiometric Ratio to Find Moles of H2SO4

From the overall reaction sequence, 1 mole of FeS2 can eventually produce 2 moles of H2SO4. So, the stoichiometric ratio between FeS2 and H2SO4 is 1:2. Therefore:

Moles of H2SO4 = 2 * Moles of FeS2 Moles of H2SO4 = 2 * 0.333 moles ≈ 0.666 moles

So, we can produce approximately 0.666 moles of H2SO4.

Step 3: Convert Moles of H2SO4 to Grams of H2SO4

To do this, we need the molar mass of H2SO4 (sulfuric acid). The molar mass of hydrogen (H) is approximately 1 g/mol, the molar mass of sulfur (S) is approximately 32 g/mol, and the molar mass of oxygen (O) is approximately 16 g/mol. So, the molar mass of H2SO4 is (2 * 1) + 32 + (4 * 16) = 2 + 32 + 64 = 98 g/mol.

Now, we can convert 0.666 moles of H2SO4 to grams:

Grams of H2SO4 = (moles of H2SO4) * (molar mass of H2SO4) Grams of H2SO4 = 0.666 moles * 98 g/mol ≈ 65.268 g

Therefore, we can obtain approximately 65.268 grams of H2SO4 from 40 g of FeS2. Looking at the options, the closest answer is C) 65.33.

Question 27: Calculating HCl Yield from H2 and Chlorine

How much hydrochloric acid is formed in the reaction of 10 g of H₂ with chlorine?

This one's about figuring out how much hydrochloric acid (HCl) we can make from reacting hydrogen (H₂) with chlorine (Cl₂). Let's break it down step by step, just like we did before.

Step 1: Write the Balanced Chemical Equation

First, we need the balanced equation for the reaction between hydrogen and chlorine to form hydrochloric acid. This is a pretty straightforward reaction:

H₂ + Cl₂ → 2 HCl

This tells us that one mole of hydrogen reacts with one mole of chlorine to produce two moles of hydrochloric acid. This balanced equation is super important because it gives us the mole ratios we need for our calculations.

Step 2: Convert grams of H₂ to moles of H₂

We're starting with 10 g of H₂, so let's convert that to moles. To do this, we need the molar mass of H₂. The molar mass of hydrogen (H) is about 1 g/mol, so the molar mass of H₂ is 2 * 1 g/mol = 2 g/mol.

Now we can calculate the moles of H₂:

Moles of H₂ = (grams of H₂) / (molar mass of H₂) Moles of H₂ = 10 g / 2 g/mol = 5 moles

So, we've got 5 moles of H₂ to start with.

Step 3: Use the Stoichiometric Ratio to Find Moles of HCl

Now, we use the balanced equation to figure out how many moles of HCl we can make. From the equation (H₂ + Cl₂ → 2 HCl), we see that 1 mole of H₂ produces 2 moles of HCl. So, the mole ratio of H₂ to HCl is 1:2.

Therefore:

Moles of HCl = 2 * Moles of H₂ Moles of HCl = 2 * 5 moles = 10 moles

This means we can produce 10 moles of HCl from 5 moles of H₂.

Step 4: Convert Moles of HCl to Grams of HCl

Finally, let's convert those moles of HCl to grams. We need the molar mass of HCl. The molar mass of hydrogen (H) is about 1 g/mol, and the molar mass of chlorine (Cl) is about 35.5 g/mol. So, the molar mass of HCl is 1 g/mol + 35.5 g/mol = 36.5 g/mol.

Now, we calculate the grams of HCl:

Grams of HCl = (moles of HCl) * (molar mass of HCl) Grams of HCl = 10 moles * 36.5 g/mol = 365 g

So, reacting 10 g of H₂ with chlorine will produce 365 grams of HCl.

Key Takeaways

Stoichiometry is Key: Understanding mole ratios from balanced equations is crucial. It's really the heart of these types of problems.
Molar Mass is Your Friend: You absolutely have to be comfortable converting between grams and moles using molar mass.
Multi-Step Reactions: For more complex reactions, like the H2SO4 production from FeS2, it's helpful to break it down into key steps to see the overall stoichiometry.

I hope this helps you guys understand how to tackle these types of stoichiometry problems. Remember, practice makes perfect, so keep at it! If you have any questions, drop them in the comments below. Happy calculating!