1. #1 What happens to atoms in a chemical reaction? Atoms are gained.
Atoms are rearranged.
Atoms are lost.
Atoms lose mass.

2. #2 Which of the following is true for ALL chemical reactions?
There are always more atoms before the reaction than after the reaction.
There are always more atoms after the reaction than before the reaction.
The number of atoms after the reaction is always equal to the number of atoms before the reaction.
The number of molecules after the reaction is always equal to the number of molecules before the reaction.

3. #3
When logs burn on a fire, the mass of the ash formed is much less than the mass of the log. Why does this not violate the Law of Conservation of Mass?
Some of the mass is converted to heat.
The ash is denser so the total mass is the same as the log.
The reaction is not a chemical reaction.
Most of the reaction products are gases so their mass is not part of the ash.

4. #4 A chemical reaction is shown below. C6H12O6 + 6O2 → 6CO2 + 6H2O
H2O and O2
C6H12O6 and CO2
CO2 and H2O
O2 and C6H12O6

5. #5 Which procedure BEST represents the law of conservation of mass?
Evaporating salt water leaves 5 grams of salt
Burning 2 kilograms of wood leaves 0.4 kilogram of ash
Using filter paper to separate 2 grams of solid from 10 grams of water
Combining 2 grams of copper and 4 grams of sulfur to produce 6 grams of copper sulfate

6. #6
A scientist wants to study what happens when carbon dioxide (CO2) reacts with hydrogen (H2). The scientists discovers that this reaction produces methane (CH4) and water (H2O). Which equation correctly represents this reaction?
CO2 + H2 → CH4 + H2O
CO H2 → CH4 + H2O
CO2 + H2 → CH4 + 2H2O
CO H2 → CH H2O

7. Calculate the number of atoms in the chemical formula: 4NaOCl 4 3 6 12#7
Calculate the number of atoms in the chemical formula: 4NaOCl 4 3 6 12

8. #8
Calculate the number of oxygen atoms on the product side of the equation below.
Al + CuSO4 → Al2(SO4)3 + Cu 2 8 12 16

9. #9 Name the compound: N2Cl5 Neon pentachloride
Dinitrogen tetrachloride
Mononitrogen tetrachloride
Dinitrogen pentachloride

10. (Hint: Write out the formula for the substance.)
#10
Your friend is very worried by rumors that he has heard about a substance called dihydrogen monoxide in the city’s water system. What could you say to your friend to calm his fears?
(Hint: Write out the formula for the substance.)

11. #11
If 100 grams of vinegar and 5 grams of baking soda are poured in a container, a small amount of gas will be produced. What will the final mass of the products be if the gas is trapped in the container?
100 grams
104 grams
105 grams
110 grams

12. #12
A chemical reaction separates water into hydrogen and oxygen gas. Which of the following statements is true about the mass of the water and the combined mass of the two gases?
The mass of the water is greater than the combined mass of the two gases.
The combined mass of the two gases is much greater than the mass of the water.
The combined mass of the two gases is the same as the mass of the water.
The mass of the water is the same as double the combined mass of the two gases.

13. #13
The conservation of mass can be demonstrated by using chemical equations. Which one below demonstrates the conservation of mass?
2Sn + 4HNO3 → SnO2 + 4NO2 + H2O
I Cl H2O → 2HIO HCl
Cl + 4Na → 4NaCl
4P + 5HNO3 → 5NO + 3H3PO4

14. #14
Carl stirred 50 grams of dry pancake mix into 30 grams of milk to make pancake batter for one pancake. What was the mass of the batter uses to make the pancake?
20 grams
50 grams
80 grams
81 grams

15. Carbon dioxide + Water + Light energy → Sugar + Oxygen
#15
Carbon dioxide + Water + Light energy → Sugar + Oxygen
The chemical equation shown above describes the process of photosynthesis that occurs in plants. A product of this process is
Carbon dioxide
Water
Oxygen
Light energy