8th STAAR review Matter and Energy

A chemist is identifying the elements present in a sample of seawater. What characteristic of an element’s atoms always determines the element’s identity?

• The number of protons
• The number of neutrons
• The location of valence electrons
• The number of valence electrons

A researcher wants to experiment with an element that reacts like phosphorus (P) but has a greater atomic mass. Which element should the researcher select for the experiment?

• Nitrogen (N)
• Sulfur (S)
• Arsenic (As)
• Silicon (Si)

*

• Boron (B)
• Carbon (C)
• Neon (Ne)
• Sodium (Na)

*

• 12CO2 + H20 --light--> C6H12O6 + O2
• CO2 + 9H20 --light--> C6H12O6 + O2
• CO2 + H20 --light--> 3C6H12O6 + O2
• 6CO2 + 6H20 --light--> C6H12O6 + 6O2

Hay is made up of organic compounds. What are the main elements in many organic compounds?

• Helium, Carbon, Sodium
• Sodium, Hydrogen, Nitrogen
• Carbon, Hydrogen, Oxygen
• Radon, Oxygen, Helium

**

• CO
• H2O
• CO2
• H2

**

• one of the original compounds came out of solution
• the solutions reacted chemically
• some of the water froze into ice crystas
• rapid evaporation of water occurred, leaving a solid

What describes the ability of a solid to dissolve in water?

• melt
• dissapear
• solubility
• evaporate

An atom of a certain element has 36 protons, 36 electrons, and a mass number of 84.  At room temperature this element is a very stable gas.  How many neutrons are in this atom?

• 48
• 36
• 84
• 120

An atom has 25 protons, 30 neutrons, and 25 electrons. What is the charge of the atom’s nucleus?

• +25
• +30
• -25
• -30