Question

1. the law of ____ states that a single compound is always composed of the same elements in the same proportions by mass. (note: length of blank line does not indicate length of correct answer.) a. conservation of energy b. conservation of mass c. definite proportions d. multiple proportions e. compounds
2. which of the following substances cannot be broken down physically or chemically? a. vinegar b. iron c. salt d. mayo e. water
3. a mixture is a. a combination of pure substances bonded chemically. b. any pure substance with a uniform composition. c. a physical combination of any two or more substances, as long as each substance retains its own chemical properties. d. any group of elements that are chemically bonded to one another.
4. matter that has a uniform and unchanging composition and cannot be physically separated is best defined as a(n) ____. a. compound b. element c. mixture d. pure substance e. colloid
5. a 10.0 g sample of magnesium reacts completely with 15.9 g oxygen to form magnesium oxide. what is the % by mass of oxygen in the product formed? a. 0.614% b. 38.6% c. 61.4% d. 62.9% e. 1.29%
6. which of the following is an intensive property of matter? a. length b. density c. volume d. mass e. these are all extensive properties.
7. an example of a homogeneous mixture is a. purified water. b. brass. c. noodle soup. d. oxygen. e. helium
8. a 76.00 g sample of an unknown compound contains 12.90 g of sulfur. what is the percentage by mass of sulfur in the compound? a. 0.1697% b. 16.97% c. 63.10% d. 88.90% e. 84.21%

Explanation:

Step1: Recall the law

The Law of definite proportions states that a single compound is always composed of the same elements in the same proportions by mass. So the answer to question 1 is c.

Step2: Identify the substance

Elements cannot be broken down physically or chemically. Iron is an element. Vinegar, salt, mayo, and water are compounds or mixtures. So the answer to question 2 is b.

Step3: Define a mixture

A mixture is a physical combination of any two or more substances, as long as each substance retains its own chemical properties. So the answer to question 3 is c.

Step4: Define a substance type

Matter that has a uniform and unchanging composition and cannot be physically separated is an element. Compounds can be chemically separated, mixtures can be physically separated, pure - substances include elements and compounds, and colloids are a type of mixture. So the answer to question 4 is b.

Step5: Calculate mass - percent

The mass of the product is the sum of the mass of magnesium and oxygen, $m = 10.0\ g+15.9\ g = 25.9\ g$. The mass - percent of oxygen is $\frac{15.9\ g}{25.9\ g}\times100\%\approx61.4\%$. So the answer to question 5 is c.

Step6: Identify intensive property

Intensive properties do not depend on the amount of matter. Density is an intensive property. Length, volume, and mass are extensive properties that depend on the amount of matter. So the answer to question 6 is b.

Step7: Define homogeneous mixture

A homogeneous mixture has a uniform composition throughout. Brass is a homogeneous mixture (an alloy). Purified water is a compound, noodle soup is a heterogeneous mixture, oxygen and helium are elements. So the answer to question 7 is b.

Step8: Calculate mass - percent of sulfur

The percent by mass of sulfur in the compound is $\frac{12.90\ g}{76.00\ g}\times 100\%=16.97\%$. So the answer to question 8 is b.

Answer:

1. c. definite proportions
2. b. iron
3. c. a physical combination of any two or more substances, as long as each substance retains its own chemical properties
4. b. element
5. c. 61.4%
6. b. density
7. b. brass
8. b. 16.97%