Q: If a compound has a mass ratio of $$\dfrac{16}{1}$$ for oxygen to hydrogen, what is the mass of oxygen in a sample containing 5 g of hydrogen?

$$16 \times 5 = 80\ \mathrm{g}$$

Question 1

Which law states that different samples of a pure chemical compound always contain the same proportions of elements by mass?

Accepted Answer

Law of Definite Proportions

Question 2

Given the chemical formula for carbon dioxide ($$\mathrm{CO_2$}$$), calculate the mass ratio of oxygen to carbon using the atomic masses: $$\mathrm{C} = 12.01\ \mathrm{g/mol}$$ and $$\mathrm{O} = 16.00\ \mathrm{g/mol}.$$

Accepted Answer

$$\dfrac{32.00}{12.01} = 2.66$$

Question 3

Two unknown compounds are examined. Compound A contains 2.0 grams of hydrogen and 32.0 grams of oxygen. Compound B contains 15.0 grams of hydrogen and 120.0 grams of oxygen. Do Compounds A and B represent the same compound according to the Law of Definite Proportions?

Accepted Answer

Yes, because the mass ratios of hydrogen to oxygen are the same.

Question 4

A compound contains only calcium and fluorine. A sample is determined to contain 2.00 g of calcium and 1.90 g of fluorine. According to the Law of Definite Proportions, how much calcium should another sample contain if it possesses 2.85 g of fluorine?

Accepted Answer

3.00 g

Question 5

A 7.74 g sample of HCN is found to contain 0.287 g of H and 4.01 g of N. What is the mass of carbon in the sample?

Accepted Answer

3.43 g

Question 6

If a compound has a mass ratio of $$\dfrac{16}{1}$$ for oxygen to hydrogen, what is the mass of oxygen in a sample containing 5 g of hydrogen?

Accepted Answer

$$16 	imes 5 = 80\ \mathrm{g}$$

Question 7

Which of the following best describes the Law of Definite Proportions?

Accepted Answer

A chemical compound always contains exactly the same proportion of elements by mass.

Question 8

A sample of a compound contains 12.0 g of carbon and 32.0 g of oxygen. What is the mass ratio of oxygen to carbon?

Accepted Answer

$$\dfrac{32.0}{12.0} = 2.67$$

Question 9

If two samples of a compound have different mass ratios of their constituent elements, what does this indicate?

Accepted Answer

They are different compounds.

Question 10

A chemist analyzes two samples: Sample X contains 10 g of element A and 40 g of element B. Sample Y contains 15 g of element A and 60 g of element B. Do these samples obey the Law of Definite Proportions?

Accepted Answer

Yes, because the mass ratio of B to A is the same in both samples.

Question 11

Which of the following is a correct application of the Law of Definite Proportions?

Accepted Answer

A compound always has the same mass ratio of its elements, regardless of sample size.

Question 12

If a sample of water contains 2 g of hydrogen and 16 g of oxygen, what is the mass ratio of oxygen to hydrogen?

Accepted Answer

$$\dfrac{16}{2} = 8$$

Question 13

A student claims that two samples with different mass ratios of elements must be the same compound. Which concept disproves this claim?

Accepted Answer

Law of Definite Proportions

Question 14

A sample of a compound contains 5.0 g of element X and 20.0 g of element Y. What is the mass ratio of Y to X?

Accepted Answer

$$\dfrac{20.0}{5.0} = 4.0$$

Question 15

If a compound is found to always contain 40% element A and 60% element B by mass, what does this illustrate?

Accepted Answer

Law of Definite Proportions

Question 16

A sample of a compound contains 8.0 g of hydrogen and 64.0 g of oxygen. What is the mass ratio of oxygen to hydrogen?

Accepted Answer

$$\dfrac{64.0}{8.0} = 8.0$$

Question 17

Which of the following is NOT a consequence of the Law of Definite Proportions?

Accepted Answer

The mass ratio of elements in a compound can vary depending on the sample.

Question 18

A compound contains 24 g of magnesium and 16 g of oxygen. What is the mass ratio of magnesium to oxygen?

Accepted Answer

$$\dfrac{24}{16} = 1.5$$

Question 19

If a compound is analyzed and found to have a mass ratio of $$2:1$$ for element X to element Y, how much of element Y is present in a 30 g sample containing only X and Y?

Accepted Answer

$$10\ \mathrm{g}$$

Law of Definite Proportions and Mass Ratio Calculations

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