## Chemistry 8 Lesson 19: Converting Mass, Volume, and Amount of Matter

## 1. Summary of theory

### 1.1. How to convert between quantity of substance and mass of substance?

1 mole of atoms (molecules) has a mass of M (grams).

n moles of atoms (molecules) have a mass of n . M (grams)

**– Comment**

Set n: number of moles of substance (mol)

M: is the molar mass of the substance (grams/mol)

m: is the mass of the substance (grams)

We multiply the number of moles of substance by the molar mass of that substance. Formula m = nM (grams) (1)

From formula (1), we can develop two related formulas as follows:

\(n = \frac{m}{M}\) and \(M = \frac{m}{n}\)

**Conclusion**

– Find the mass of substance (m) when knowing the number of moles of substance (n), we find the molar mass (M) of the substance, then apply the formula: m = n . M (grams)

– Find the number of moles of substance (n) when knowing the mass of substance (m), we find the molar mass (M), then apply the formula:

– Find the molar mass (M) when knowing the number of moles (n) and the mass (m), we apply the formula:

### 1.2. How is the volume of a substance and the volume of a gas converted?

1 mole of atoms (molecules) has a volume of 22.4 (liters).

n moles of atoms (molecules) have a volume of 22.4 . n (liters)

**Comment:**

Set n: number of moles of substance (mol)

V: Volume of substance at standard conditions (liter)

We take the number of moles of substance multiplied by 22.4. The formula V = 22.4 . n (lit) (2)

From formula (2), we can develop the related formula:

**Conclusion**

– Find the volume of the gas we use the formula: V = 22.4 . n (liters)

– Find the number of moles of gas

## 2. Illustrated exercise

### 2.1. Form 1: Convert between quantity of substance and mass of substance

**Lesson 1: **Calculate the mass of the following substances:

a) 0.5 moles of N . atoms

b) 0.1 mole of Cl . molecules_{2}

c) 0.5 mol CuSO_{4}

__Solution guide__

a) The mass of 0.5 mol N is:

m = nM = 0.5 . 14 = 7 (grams)

b) Mass of 0.1 mol Cl_{2} to be:

m = nM = 0.1 . 71 = 7.1 (grams)

c) Mass of 0.5 mole of CuSO_{4} to be:

m = nM = 0.5 . 160 = 80 (grams)

**Lesson 2: **Applying the formula, complete the following exercise:

a) Calculate the mass of 0.25 moles of N2 . molecules

b) What is the number of moles of 32g Cu?

__Solution guide__

Apply the formula: m = n. USA

โ Mass of 0.25 mole of N . molecule_{2} is 0.25. 28 = 7 (grams)

**Lesson 3: **Calculate the molar mass of compound A, given that 0.125 moles of this substance has a mass of 12.25 grams?

__Solution guide__

Apply the formula: \(M = \frac{m}{n}\)

The molar mass of compound A is: 12.25 : 0.125 = 98

### 2.2. Form 2: Convert between quantity of substance and volume of gas

Said

a) 0.2 mol O_{2} how many liters in dtc?

b) 1.12 (liters) of oxygen gas at dtc is how many moles?

__Solution guide__

a) The volume of oxygen gas (dktc): 0.2,22.4 = 4.48 liters

b) Number of moles of oxygen gas: 1.12 : 22.4 = 0.05 mol

## 3. Practice

### 3.1. Essay exercises

**Question 1:** Volume of CH_{4} in dktc when knowing m = 96 g?

**Verse 2:** The number of moles of C atoms in 44 g CO_{2}?

**Question 3:** How many moles of C atoms are needed to get 2.4.10^{23} C atom?

**Verse 4:** Molars of 19.6 g H_{2}SO_{4 }to be?

### 3.2. Multiple choice exercises

**Question 1:** Given the following equation, calculate the mass of the substance formed knowing 2.3 g Na

4Na + O_{2} โ 2Na_{2}O

A. 0.31 g

B. 3 g

C. 3.01 g

D. 3.1 g

**Verse 2:** For Fe + HIM_{2}SO_{4} โ FeSO_{4} + FRIENDS_{2}. Calculating DRESS_{H}_{2} know me_{Fe} = 15.12 g

A. 6,048 l

B. 8,604 l

C. 5.122 l

D. 2.45 l

**Question 3:** Choose the correct answer: The number of moles of 12g O_{2}, 1.2 g H_{2}, 14 g WOMEN_{2}

A. 0.375 mol; 0.6 mol; 0.5 mol

B. 0.375 mol; 0.5 mol; 0.1 mol

C. 0.1 mol; 0.6 mol; 0.5 mol

D. O,5 mol; 0.375 mol; 0.3 mol

**Verse 4:** If two different substances, present at the same temperature and pressure, have the same volume, then

A. Same mass

B. Same number of moles

C. Same chemical properties

D. Same physical properties

**Question 5:** For me_{Shift} = 5 g, m_{High} = 5.6 g. Correct conclusion

A. n_{Shift} > n_{High}

B. n_{Shift} < n_{High}

CN_{Shift} = n_{High}

D. DRAW_{Shift} = DRAW_{High}

## 4. Conclusion

After the lesson to know:

- Know the relationship between mass and quantity of substance.
- Determine the mass, quantity, and molar mass of the substance when the other two quantities are known.

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