Matter/Isotopes/Molarity

After two elements react in a closed container, the ratio of their masses in the container will be the same as before the reaction. Which law describes this principle?

• Law of definite proportions

• Law of multiple proportions

• Law of conservation of mass

• Law of conservation of energy

Magnesium can react explosively with oxygen to form magnesium oxide. Which is NOT true of this reaction?

• The mass of magnesium oxide produced equals the mass of magnesium consumed plus the mass of oxygen consumed.

• The reaction describes the formation of a new susbtance.

• The product of the reaction, magnesium oxide, is a chemical compound.

• Magnesium oxide has physical and chemical properties similar to both oxygen and magnesium.

Which method would best for separating alcohol from water? (ethanol boils at 173°F, water boils at 212°F)

• Filtration

• Chromatography

• Magnet

• Distillation

If 45.98 g of sodium combines with enough chlorine to form 116.89 g of sodium chloride, what mass chlorine gas is used in the reaction?

• 35.45 g

• 70.91 g

• 45.98 g

• 116.89 g

Carbon dioxide is a gas that is produced as a waste product of cellular respiration in cells. What is the percent by mass of carbon in 44.0 g of carbon dioxide? (hint - look at periodic table)

• 73%

• 27%

• 44%

• 12%

An isotope of iron (Fe) has a mass number of 56 amu. How many neutrons are found in the nucleus of this isotope?

• 82

• 56

• 30

• 26

Calculate the average atomic mass of an unknown element-X. Then, using that data and the data below plus the periodic table, determine the identity of the element.

First isotope of X = mass of 6.015 amu, percent abundance 7.59%

Second Isotope of X = mass of 7.016 amu, percent abundance 92.41%

• Hydrogen

• Lithium

• Nitrogen

• Carbon

Which subatomic particle identifies an atom as that of a particular element?

• Proton

• Neutron

• Electron

• Positron

Ethanol is a common ingredient found in beer and wine. It is a product of fermentation in yeast. Calculate the molar mass of ethanol (C₂H₅OH).

• 30.67 g/mol

• 46.07 g/mol

• 92.14 g/mol

• 100.05 g/mol

11.0 g of calcium chloride (CaCl₂) is dissolved in 500.0 mL of water to make a solution. What is the molarity of the resulting solution?

• 2.00 M

• 0.20 M

• 0.40 M

• 4.00 M