Q: A student mixes 10 g of reactant A with 15 g of reactant B. The reaction produces 8 g of product C. If the theoretical yield is 10 g, what is the percent yield?

$$\frac{8}{10} \times 100\% = 80\%$$

Q: Which equation correctly calculates the mass percent of element A in a compound?

$$\frac{\text{mass A in compound}}{\text{compound mass}} \times 100\%$$

Q: A reaction table shows that 5 g of reactant X is used, and 2 g remains after the reaction. What is the percent excess of X?

$$\frac{2}{(5-2)} \times 100\% = 66.7\%$$

Q: A compound contains 40 g of element A and 60 g of element B. What is the mass percent of element A?

$$\frac{40}{100} \times 100\% = 40\%$$

Q: A reaction produces 12 g of product, but the theoretical yield is 15 g. If 3 g of reactant remains unused, what is the percent yield?

$$\frac{12}{15} \times 100\% = 80\%$$

Q: A reaction table shows that 10 g of reactant Y was used, and 4 g was left over. What is the percent excess?

$$\frac{4}{6} \times 100\% = 66.7\%$$

Question 1

Which of the following best describes the empirical formula of a compound?

Accepted Answer

It represents the simplest ratio of elements in a compound.

Question 2

Benzene has a molecular formula of $$\mathrm{C_6H_6}. $$What is its empirical formula?

Accepted Answer

$$\mathrm{CH}$$

Question 3

A student mixes 10 g of reactant A with 15 g of reactant B. The reaction produces 8 g of product C. If the theoretical yield is 10 g, what is the percent yield?

Accepted Answer

$$\frac{8}{10} 	imes 100\% = 80\%$$

Question 4

Which equation correctly calculates the mass percent of element A in a compound?

Accepted Answer

$$\frac{	ext{mass A in compound}}{	ext{compound mass}} 	imes 100\%$$

Question 5

A reaction table shows that 5 g of reactant X is used, and 2 g remains after the reaction. What is the percent excess of X?

Accepted Answer

$$\frac{2}{(5-2)} 	imes 100\% = 66.7\%$$

Question 6

Which of the following statements about significant figures is correct?

Accepted Answer

The number of significant figures reflects the precision of a measurement.

Question 7

If a chemical equation is not balanced, which law is violated?

Accepted Answer

Law of Conservation of Mass

Question 8

A compound contains 40 g of element A and 60 g of element B. What is the mass percent of element A?

Accepted Answer

$$\frac{40}{100} 	imes 100\% = 40\%$$

Question 9

Which of the following is NOT a skill to master for biochemistry calculations?

Accepted Answer

Memorizing historical dates

Question 10

A reaction produces 12 g of product, but the theoretical yield is 15 g. If 3 g of reactant remains unused, what is the percent yield?

Accepted Answer

$$\frac{12}{15} 	imes 100\% = 80\%$$

Question 11

Which scenario best illustrates the concept of limiting reactant?

Accepted Answer

A reaction stops when one reactant is completely used up.

Question 12

If the empirical formula of a compound is $$\mathrm{CH_2$}$$ and its molecular mass is 56 g/mol, what is its molecular formula?

Accepted Answer

$$\mathrm{C_4H_8}$$

Question 13

A biochemist needs to convert 0.5 moles of glucose ($$\mathrm{C_6H_{12}O_6$}) to $$grams. If the molar mass of glucose is 180 g/mol, what is the mass?

Accepted Answer

$$0.5 	imes 180 = 90 g$$

Question 14

Which of the following best describes the difference between theoretical yield and actual yield?

Accepted Answer

Theoretical yield is the maximum possible product, while actual yield is what is actually obtained.

Question 15

A reaction table shows that 10 g of reactant Y was used, and 4 g was left over. What is the percent excess?

Accepted Answer

$$\frac{4}{6} 	imes 100\% = 66.7\%$$

Question 16

Which of the following is an example of a unit conversion relevant to biochemistry?

Accepted Answer

Converting grams to moles using molar mass

Question 17

A compound has a mass of 120 g and contains 30 g of element Z. What is the mass percent of Z?

Accepted Answer

$$\frac{30}{120} 	imes 100\% = 25\%$$

Question 18

Which of the following is NOT provided by the empirical formula?

Accepted Answer

The actual number of atoms in a molecule

Question 19

A reaction produces 20 g of product, but the theoretical yield is 25 g. What is the percent yield?

Accepted Answer

$$\frac{20}{25} 	imes 100\% = 80\%$$

Chapter 1: Biochemistry and the Language of Chemistry – Key Concepts and Calculations

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