Question

q 1.21 in a chemical equation, the substances formed are called _____
a reactants
b products
c coefficients
d subscripts

q 1.22 according to the law of conservation of mass, mass is _____
a created during reactions
b destroyed during reactions
c always increasing
d neither created nor destroyed

q 1.23 what is the si unit for amount of substance?
a gram
b liter
c mole
d meter

q 1.24 which number has the greatest precision?
a 8 cm
b 8.0 cm
c 8.00 cm
d all are equal

Explanation:

Identify substances formed in chemical equations

In a chemical reaction, starting substances are reactants. The new substances formed are products. This relates to Chemical Reactions.

• Option A: Reactants are starting materials.
• Option B: Products are the formed substances.
• Option C: Coefficients show molecule ratios.
• Option D: Subscripts show atom ratios.

Analyze the Law of Conservation of Mass

The Law of Conservation of Mass states mass is conserved.

• Mass cannot be created or destroyed in a chemical reaction.
• Therefore, option D is correct.

Determine the SI unit for amount of substance

We look at standard SI base units:

• Gram is for mass (though kilogram is the SI base unit).
• Liter is a unit of volume.
• Mole is the SI base unit for amount of substance.
• Meter is for length.
• Therefore, option C is correct.

Compare the precision of the measurements

Precision is indicated by the number of decimal places or significant figures.

• \(8\text{ cm}\) is precise to the nearest \(1\text{ cm}\).
• \(8.0\text{ cm}\) is precise to the nearest \(0.1\text{ cm}\).
• \(8.00\text{ cm}\) is precise to the nearest \(0.01\text{ cm}\).
• Therefore, \(8.00\text{ cm}\) has the greatest precision (Option C).

Answer:

Question 1.21

• A reactants
• B products (Correct answer)
• C coefficients
• D subscripts

Question 1.22

• A created during reactions
• B destroyed during reactions
• C always increasing
• D neither created nor destroyed (Correct answer)

Question 1.23

• A gram
• B liter
• C mole (Correct answer)
• D meter

Question 1.24

• A 8 cm
• B 8.0 cm
• C 8.00 cm (Correct answer)
• D All are equal