Chemical Equations and Law of Conservation of Mass Quiz

Isla and Elijah are in the science lab, and they just mixed sodium (Na) with water (H₂O) to see what happens! The reaction is:

Na + H₂O → NaOH + H₂

Can you help Isla and Elijah figure out if this equation is balanced or unbalanced? Justify your answer by counting the atoms on each side!

• Balanced; sodium, oxygen, and hydrogen counts match on both reactant and product sides.

• Unbalanced; hydrogen atoms are not equal between the reactant and product sides.

• Unbalanced; sodium atoms differ between the reactant and product sides.

• Balanced; nitrogen, oxygen, and hydrogen counts match on both reactant and product sides.

Answer explanation

Na + H₂O → NaOH + H₂

Na: 1 Na: 1 😄

H: 2 H: 3 😞

O: 1 O: 1 😄

Since the hydrogen are unbalanced, this equation breaks the law of conservation of mass.

Tags

TEKS.SCI.8.6E

2H₂ + O₂ → 2H₂O

__ g + 15 g → 40 g

According to the Law of Conservation of Mass, how many grams of hydrogen are needed for the reaction if 15 g of oxygen reacts to produce 40 g of water?

Mathematical Equivalence

ON

Answer explanation

__ g + 15 g → 40 g

Subtract 15 g from both sides to get the blank by itself.

40 g - 15 g = 25 g

Tags

TEKS.SCI.8.6E

Abigail is conducting a chemistry experiment. She writes an equation where the atom counts for each element match on both sides. This equation is called (a)   .

Answer explanation

When the number of atoms on the reactant side are equal to the number of atoms on the product side, the equation is balanced.

Tags

TEKS.SCI.8.6E

Emma and Mia are conducting a cool chemistry experiment together!

Take a look at their setup and help them fill in the blanks.

The experiment shows a ​ (a)   system.

The mass at the end of Emma and Mia's experiment will be ​ (b)   the initial mass.

• closed
• open

• equal to
• less than

• greater than

Answer explanation

Since there is a cork on the E. flask, this is a closed system. The matter cannot escape and it should demonstrate the law of conservation of mass because the mass of the reactants should be equal to the mass of the products.

Tags

TEKS.SCI.8.6E

A chemical equation for the reaction between calcium hydroxide Ca(OH)_2, and sulfuric acid, H₂SO₄, is shown. The masses of some of the reactants and products are given in grams.

According to the Law of Conservation of Mass, how many grams of sulfuric acid were used in this reaction?

Mathematical Equivalence

ON

Answer explanation

Step 1: Add the two formulas on the product side together:

136 g + 36 g = 172g

74 g + __ g = 172 g

Step 2: Subtract 74 g from both sides:

172g - 74g = 98g

Tags

TEKS.SCI.8.6E

New substances are formed when the ​ (a)   of substances are rearranged during a​ (b)   reaction. The law of ​ (c)   of mass states that the total number of atoms of each ​ (d)   is not created or ​destroyed during a chemical reaction. Instead, the atoms are ​ (e)   to form new substances.

• atoms
• chemical
• conservation
• element
• rearranged
• compound
• physical
• destroyed
• created

Tags

TEKS.SCI.8.6E

The ​ (a)   states that the same amount of ​ (b)   in the ​ (c)   must be present after a reaction in the ​ (d)   . So, if 2g oxygen react with 3g hydrogen, the water they form will have a mass of ​ (e)   .

• Law of Conservation of Mass
• matter/mass
• reactants
• products
• 5g
• Law of Inertia
• volume
• 1g
• 6g
• Law of Conservation of Energy

Tags

TEKS.SCI.8.6E

Michael, Anika, and Ethan are in a chemistry challenge! Can you help them balance this equation so they can win the prize?

​ (a)   Fe + ​ (b)   O₂ --> ​ (c)   Fe₂O₃

• 3
• 2
• 1

• 4
• 0

Answer explanation

You need the same number of atoms on each side of the equation. You can only change the coefficient .

Find the number factor for the oxygen on both sides, first.

They can both be multiplied a number to equal six (6).

Put a "3" in front of the O₂ on the reactant side and a 2 in front of formula for Fe₂O₃ on the product side for them to both have 6 atoms of oxygen.

This is because 2O₃ = 6 atoms of O; 3O₂ = 6 atoms of O

This now creates 4 atoms of iron (Fe) on the product side since 2Fe₂ = 4 atoms of Fe. To get Fe equal on both sides, you need to put a 4 in front of Fe on the reactant side because 2Fe₁ = 2 atoms of Fe

Tags

TEKS.SCI.8.6E

Match the correct part of the chemical equation with its descriptor.

• Reactants

• A

• Coefficient

• D

• Products

• E

• Yields

• B

• Subscript

• C

Tags

TEKS.SCI.8.6E

Kai is conducting a science experiment where he mixes two different substances, represented by the black and white circles. He observes the reaction and records the models below. Which of the models of a chemical reaction best represents the Law of Conservation of Mass?

• A

• B

• C

• D

Answer explanation

A) Reactant: 4 small black circles and 2 large white circles.

Product: small black circles and 2 large white circles.

This is balanced.

B) Reactant: 3 small black circles; 1 large white circle

Product: 2 small black circles 1 large white circle

This is unbalanced.

C) Reactant: 2 small black circles; 2 large white circles

Product: 4 small black circles; 2 large white circles

This is unbalanced.

D) Reactant: 2 small black circles; 3 large white circles

Product: 3 small black circles; 1 large white circle

This is unbalanced.

Tags

NGSS.MS-PS1-2

NGSS.MS-PS1-5