Density
Calculations
Calculations
A sample has a mass of 60 g and a volume of 20 mL. What is its density?
3 g/mL.
60 ÷ 20 = 3.
An ice cube melts into water. Is this a physical or chemical change?
Physical change.
It is still water; only its state changes.
A solution has a pH of 4. Is it acidic, basic, or neutral?
Acidic.
pH values below 7 are acidic.
A process absorbs energy from its surroundings. Endothermic or exothermic?
Endothermic.
Energy is taken in.
A sealed container has 80 g of matter before a reaction. What is its total mass afterward?
80 g.
Matter cannot be created nor destroyed.
A rock has a mass of 75 g. Water rises from 40 mL to 55 mL. What is the rock’s density?
5 g/mL.
Volume = 55 − 40 = 15 mL; density = 75 ÷ 15 = 5 g/mL.
An iron bicycle chain develops rust. Physical or chemical change?
Chemical change.
Rust is a new substance formed by a reaction.
A cleaner has a pH of 10. Is it acidic, basic, or neutral?
Basic.
pH values above 7 are basic.
A reaction releases energy to its surroundings. Endothermic or exothermic?
Exothermic.
Energy exits
In a chemical equation, what do we call the substances on the left of the arrow?
Reactants.
The arrow points from reactants to products.
A metal has a density of 2.5 g/cm³ and a volume of 8 cm³. What is its mass?
20 g.
Mass = density × volume = 2.5 × 8.
Sugar dissolves in warm tea. Physical or chemical change, and why?
Physical change.
Dissolving sugar does not produce a new substance.
Which is a chemical property: acidity or solubility?
Acidity.
Solubility is a physical property; acidity is a chemical property.
Breaking chemical bonds requires more energy than forming new bonds releases. Is the overall reaction endothermic or exothermic?
Endothermic.
More energy is absorbed than released.
Why must chemical equations be balanced?
To show the same number of atoms of each element on both sides.
Atoms are rearranged, not created or destroyed.