RC

What does the Law of Conservation of Mass state?

• Matter cannot be gained or lost in a chemical reaction.

• Matter can only be lost in a chemical reaction.

• Matter can only be gained in a chemical reaction.

• Matter can be gained and lost in a chemical reaction. 

Tags

NGSS.MS-PS1-5

A teacher is demonstrating physical and chemical changes to her class. Which action should she use to demonstrate a chemical change?

• cutting a piece of paper

• folding a piece of paper

• tearing a piece of paper

• burning a piece of paper

Tags

NGSS.MS-PS1-2

Which of the following could be the chemical formula for sulfuric acid (shown in the picture)? (8.5D)

• HSO

• HSO₄

• H₂SO₄

• HS₂O₄

Tags

NGSS.MS-PS1-1

A student observes some sugar as it is heated and burns. The student concludes that a chemical reaction has occurred. Which of the following observations about the burning sugar provides evidence of a chemical reaction? (8.5E)

• Heat is added to the sugar crystals.

• The sugar melts and becomes a liquid.

• The temperature of the sugar increases.

• Gas is produced as the sugar turns black.

Tags

NGSS.MS-PS1-2

Coal contains carbon and other elements. Carbon dioxide forms when coal burns in the presence of oxygen. Which of these is the best evidence that a chemical reaction occurs when coal burns?

• The shape of the coal changes

• Oxygen is present

• A new substance is produced

• Coal is made up of more than one element

Tags

NGSS.MS-PS1-2

Four students performed four different investigations by combining different substances. Which of the observations is most indicative of a chemical reaction?

• investigation 1

• investigation 2

• investigation 3

• investigation 4

Tags

NGSS.MS-PS1-2

NGSS.MS-PS1-5

You know that a chemical reaction is occurring here because you see __________________ . (Pick 3)

• purple color

• smoke

• ice formation

• fire

• a yellow precipitate

Tags

NGSS.MS-PS1-2

Which of the following describes a precipitate?

• a liquid forms when a block of metal is heated

• a solid forms when one liquid is poured into another

• a gas forms when a solid is placed in a liquid

• bubbles form when an acid is poured on a rock

Tags

NGSS.MS-PS1-2

Which pair of properties describes the elements in Group 18?

• They are chemically stable and liquid at room temperature.

• They have eight valence electrons and are flammable.

• They are magnetic and boil at low temperatures.

• They are gaseous at room temperature and chemically stable.

Answer explanation

The elements of Group 18 are nonreactive (chemically stable) gases.

A student is studying Calcium (Ca), a highly reactive element that humans need for strong bones. Which characteristics of calcium is most closely related to its chemical reactivity?

• The 20 protons in each atom of calcium

• The density of calcium which is 1.54 g/cm³

• The atomic mass of calcium which is 40.078 amu

• The 2 valence electrons in each atom of calcium

Answer explanation

The number of valence electrons in the atom determines the reactivity of the element.

Tags

NGSS.HS-PS1-1

NGSS.HS-PS1-2