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Sodium reacts with chlorine to form the compound sodium chloride, or salt. The chemical formula below shows how the two elements combine into a compound.

2Na + Cl2 → 2NaCl

If the total mass of the reactants is 58.44 amu, what will be the total mass of the products?

(1 point)
Responses

60 amu
60 amu

116.88 amu
116.88 amu

58.44 amu
58.44 amu

29.22 amu

11 answers

According to the law of conservation of mass, the total mass of the reactants must be equal to the total mass of the products in a chemical reaction. Therefore, if the total mass of the reactants is 58.44 amu, the total mass of the products must also be 58.44 amu.

The correct response is:

58.44 amu

Which procedure could be used to demonstrate that matter is conserved during a physical change?(1 point)
Responses

Find the mass of a cup of water. Boil the water. Find the mass of the water that remains.
Find the mass of a cup of water. Boil the water. Find the mass of the water that remains.

Find the mass of a piece of ice. Let the ice melt. Find the mass of the liquid water.
Find the mass of a piece of ice. Let the ice melt. Find the mass of the liquid water.

Find the mass of a raw egg. Cook the egg. Find the mass of the cooked egg.
Find the mass of a raw egg. Cook the egg. Find the mass of the cooked egg.

Find the mass of an apple. Cut the apple and remove the core. Find the mass of the remaining apple.

To demonstrate that matter is conserved during a physical change, you want to perform an experiment where you can measure the mass before and after a change that does not involve a chemical transformation.

The best procedure from the options given is:

"Find the mass of a piece of ice. Let the ice melt. Find the mass of the liquid water."

This procedure shows that when ice (a solid) melts to become water (a liquid), the total mass remains the same, demonstrating that matter is conserved during the physical change of melting.

One molecule of bromine (Br2) and two molecules of potassium chloride (KCl) combine in a reaction. How many atoms are in the products?(1 point)
Responses

three
three

four
four

two
two

six

To determine the number of atoms in the products when one molecule of bromine (Br2) and two molecules of potassium chloride (KCl) combine, we first need to break down the composition of each reactant:

  1. Bromine (Br2): This molecule has 2 bromine atoms.
  2. Potassium Chloride (KCl): Each molecule of KCl contains 1 potassium atom and 1 chlorine atom. Since there are 2 molecules of KCl, this contributes:
    • 2 potassium atoms
    • 2 chlorine atoms

Now, let's sum the total number of atoms from all reactants:

  • From Br2: 2 Br atoms
  • From 2 KCl: 2 K atoms + 2 Cl atoms = 4 atoms (2 K + 2 Cl)

Now, we add them together:

  • Total = 2 (Br) + 2 (K) + 2 (Cl) = 6 atoms

So, the total number of atoms in the products is six.

The correct response is:

six

Use the unbalanced chemical equation to answer the question.

2NaHCO3 → Na2CO3 + CO2

Which of the following can be added to the products to balance the equation?

(1 point)
Responses

H2
H 2

CH2OH
CH 2 OH

H2O
H 2 O

O2

To balance the given chemical equation:

Unbalanced equation: \[ 2 \text{NaHCO}_3 \rightarrow \text{Na}_2\text{CO}_3 + \text{CO}_2 \]

Let’s break down the reactants and products:

  • Reactants:

    • 2 Na (from 2 NaHCO3)
    • 2 H (from 2 NaHCO3)
    • 2 C (1 from Na2CO3 and 1 from CO2, total of 2)
    • 6 O (from 2 NaHCO3 contributing 3 per molecule, total of 6)

  • Products:

    • 2 Na (from Na2CO3)
    • 2 C (1 from Na2CO3 and 1 from CO2)
    • 5 O (3 from Na2CO3 and 2 from CO2)

Currently, the equation is not balanced because the number of oxygen atoms on the products side is 5, while there are 6 on the reactant side (according to the breakdown above).

To balance the number of oxygen atoms, we can look for a compound that can provide one additional oxygen atom without disturbing the balance of other elements.

Of the options given:

  • H2: does not provide oxygen
  • CH2OH: does not provide oxygen (it contains 1 O)
  • H2O: provides 1 O, making the total oxygen count 6
  • O2: provides 2 O, which would unbalance the equation further

The correct addition to balance the equation is:

H2O

In 1-2 sentences, explain why creating models, like the one shown in the image above, is important in understanding substances.

Creating models of substances is important because they allow us to visualize and analyze molecular structures, interactions, and behaviors that are not easily observed in real life. These models enhance our understanding of chemical properties and reactions, making it easier to predict how substances will behave under different conditions.

Copper (Cu) reacts with sulfur (S) to form copper sulfide as shown in the equation. A scientist adds 12.7 grams of Cu to 3.2 grams of S to start the reaction. In this reaction, all of the copper and all of the sulfur react. Before running the experiment, the scientist expected the products of the reaction will be a total of 15.9 grams of copper sulfide (Cu2S). In 1–2 sentences, explain the law that the scientist used to predict that the product of the reaction would be 15.9 grams of copper sulfide.

(2 points)

The scientist used the law of conservation of mass to predict the mass of the copper sulfide product, which states that in a closed system, the total mass of reactants before a chemical reaction must equal the total mass of products after the reaction. Since the total mass of the reactants (12.7 grams of Cu and 3.2 grams of S) is 15.9 grams, the scientist expected that the mass of the copper sulfide produced would also be 15.9 grams.