Elements
count atoms
chemical reactions
STAAR Release
100
How many elements are represented in the following formula C2H4O?
3 Elements
Carbon, Hydrogen, Oxygen
100
How many Al atoms are in this compound? 4Al2O3
A. 8
B. 2
C. 4
D. 6
A. 8
100
Which statement describes an action that most likely resulted in a chemical reaction?
A. A broken pencil.
B. Gas bubbles formed after adding the mentos into a soda bottle.
C. A liquid was sprayed into the air, and a sweet odor was smelled.
D. An ice cube melting.
B. Gas bubbles formed after adding the mentos into a soda bottle.
100
Based on the reaction shown, which statement best SUPPORTS the Law of Conservation of Mass?
Zn + 2HCl -----> ZnCl2 + H2
A. There are more chlorine atoms in the reactant.
B. There are more hydrogen atoms in the product.
C. The number of chlorine atoms is unequal in the reactants and products.
D. The number of reactant atoms is equal to the number of product atoms.
D. The number of reactant atoms is equal to the number of product atoms.
200
How many elements are found in 2H2(SO4)ClMg?
A. 2
B. 3
C. 4
D. 5
D. 5
200
Boric acid, B(O2H)3 , it is usually encountered as colorless crystals or a white powder, that dissolves in water. Sodium bicarbonate, Na(HC)O2, is commonly known as baking soda.
How many more oxygen atoms are represented in the formula for boric acid than in the formula for Sodium bicarbonate?
A. 5
B. 4
C. 2
D. 1
B. 4
200
Which of these observations is an indication that a chemical reaction has occurred?
A. A solid forms when two clear solutions are mixed.
B. No new substance is formed.
C. Salt dissolving in water.
D. A solid forms when a clear solution is frozen.
A. A solid forms when two clear solutions are mixed.
200
Students are baking a cake. They mix together all the necessary ingredients and pour them into a pan. Then they place the pan into the oven to cook for 40 minutes.
Which statement BEST explains why baking a cake is evidence of a chemical reaction?
A. The state of matter of some of the ingredients changed while being cooked.
B. The total mass of the ingredients was the same before and after they were cooked.
C. The temperature of the ingredients increased as they absorbed thermal energy from the oven.
D. The ingredients formed a new substance after they were cooked in the oven.
D. The ingredients formed a new substance after they were cooked in the oven.
300
What is the number of Elements in the Reactants?
2Na + Cl₂--------- 2NaCl
A. 2
B. 4
C. 6
D. 8
A. 2
300
Which balanced equation represents a reaction that involves 18 atoms of Hydrogen?
F. NH9Cl + KOH9 → N2H9 + B2O
G. 2Na + 2H2O → 2NaOH + H2
H. 2C2H6 + 7O2 → 4CO2 + 6H2O
F. NH9Cl + KOH9 → N2H9 + B2O
300
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?
A. Heat is added to the sugar crystals.
B. Gas is produced as the sugar turns black.
C. The sugar melts and becomes a liquid.
B. Gas is produced as the sugar turns black.
300
A balanced chemical equation is shown.
2Fe + 6HC2H3O2 → 2Fe(C2H3O2)3 + 3H2
How many different elements are in the chemical equation?
A. 2
B. 4
C. 13
D. 50
B. 4
400
What is the number of Elements in the Products?
CH₄ + O₂ → CO₂ + 2H₂O
A. 7
B. 3
C. 4
D. 2
B. 3
400
How many atoms of each element are represented in the formula below?
(Mg4H2O3)
There are 4 atoms of Magnesium, 2 atoms of Hydrogen and 3 atoms of Oxygen.
400
Which of the following is an example of a chemical reaction?
A. Burning wood turns into ashes.
B. Chopping wood into smaller pieces.
C. Cutting paper into smaller pieces.
D. Food coloring in water.
A. Burning wood turns into ashes.
400
A compound secreted by honeybees to paralyze intruders in their hive is known as 2-heptanone. The formula for this compound is shown. CH3C4 H8COCH3
How many atoms of each element are in one molecule of 2-heptanone?
A. 4 carbon atoms, 11 hydrogen atoms, and 1 oxygen atom
B. 7 carbon atoms, 14 hydrogen atoms, and 1 oxygen atom
C. 7 carbon atoms, 11 hydrogen atoms, and 8 oxygen atoms
D. 6 carbon atoms, 14 hydrogen atoms, and 3 oxygen atoms
B. 7 carbon atoms, 14 hydrogen atoms, and 1 oxygen atom
500
What is the number of elements in Acetic Acid?
CH₃COOH
A. 6
B. 9
C. 3
D. 5
C. 3
500
Which chemical reaction involves the fewest Hydrogen atoms?
A.
B.
C.
C.
500
Which statement best describes evidence that a chemical reaction occurs as a cake bakes?
A. The water in the cake batter evaporates.
B. The cake rises as gas bubbles form in the baking cake.
C. The cake takes the shape of the container in which it is baked.
D. The water in the cake batter is used to keep the cake moist as it bakes.
B. The cake rises as gas bubbles form in the baking cake.
500
Students mixed two liquids in a beaker and listed their observations.
Liquid 1 was colorless.
Liquid 2 was colorless.
The mixture of liquids 1 and 2 formed a colorless solution.
Small, solid particles formed and fell to the bottom of the beaker.
Based on these observations, which statement contains the best evidence that a chemical reaction occurred?
A There is a change in shape.
B There is a change in volume.
C The two liquids mix into a solution.
D The two liquids form a new substance.
D The two liquids form a new substance.