Question

day 3 - 8th grade science staar review
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date

1. which of the following chemical equations for a reaction between carbon, carbon dioxide and water is correctly balanced?

a ( 3co_2 + 6h_2o
ightarrow c_6h_{12}o_6 + 3o_2 )
b ( 6co_2 + 6h_2o
ightarrow c_6h_{12}o_6 + 6o_2 )
c ( 3co_2 + 2h_2o
ightarrow c_6h_{12}o_6 + 3o_2 )
d ( co_2 + h_2o
ightarrow c_6h_{12}o_6 + o_2 )

1. in question #9, what is the mass of the products compared to the mass of the reactants?

a the mass of the products is equal to the mass of the reactants.
b the mass of the products of the chemical reaction is always greater than the reactants.
c some of the mass is lost in the reaction, so the mass of the reactants is greater.
d there is not enough information. it depends on the conditions of the reaction.

1. why is it important for a chemist to have a balanced chemical equation for a reaction?

a she will need to be able to predict the right temperature for the reaction to occur.
b not having the right amounts of reactants will cause the reaction to be dangerous.
c in order to produce the desired amount of product, she will need to know the ratios of the reactants to use.
d unbalanced equations will cause her not to use the right lab equipment.

1. a beaker with two liquid compounds is placed on a hot plate and heated. what question can be best answered from this experiment?

image of a hot plate with a beaker
a at what temperature will the substances boil?
b which substance will float on the other?
c which substance will freeze first?
d will the substances conduct electricity?

Explanation:

Step1: Balance question 9 equation

Reaction: glucose ($\text{C}_6\text{H}_{12}\text{O}_6$) + oxygen ($\text{O}_2$) → carbon dioxide ($\text{CO}_2$) + water ($\text{H}_2\text{O}$)
Balanced: $\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2
ightarrow 6\text{CO}_2 + 6\text{H}_2\text{O}$ (matches option B)

Step2: Answer question 10

Law of conservation of mass: mass of products = mass of reactants (option A)

Step3: Answer question 11

Balanced equations show reactant/product mole ratios, needed for product yield (option C)

Step4: Answer question 12

Heating liquids tests boiling temperature (option A)

Answer:

1. B. $\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2

ightarrow 6\text{CO}_2 + 6\text{H}_2\text{O}$

1. A. The mass of the products is equal to the mass of the reactants.
2. C. In order to produce the desired amount of product, she will need to know the ratios of the reactants to use.
3. A. At what temperature will the substances boil?