Question

section 3.4 elements and compounds
in your textbook, read about elements and compounds.
circle the letter of the choice that best completes the statement or answers the question.

1. a substance that cannot be separated into simpler substances by physical or chemical means is a(n)

a. compound.
b. mixture.
c. element.
d. period

1. a chemical combination of two or more different elements is a(n)

a. solution.
b. compound.
c. element.
d. period

1. which of the following is an example of an element?

a. water
b. air
c. sugar
d. oxygen

1. which of the following is an example of a compound?

a. gold
b. silver
c. aspirin
d. copper

1. what are the horizontal rows in the periodic table called?

a. block elements
b. groups or families
c. grids
d. periods

1. what are the vertical columns in the periodic table called?

a. block elements
b. groups or families
c. grids
d. periods
label each substance as either an element or a compound.

1. silicon
2. sodium chloride
3. francium
4. nickel
5. ice

write the symbol for each element. use the periodic table on pages 72 - 73 in your textbook if you need help.

1. neon
2. calcium
3. iron
4. titanium
5. fluorine

in your textbook, read about the law of definite proportions.
use the law of definite proportions and the equation below to answer the questions.
the law of definite proportions states that regardless of the amount, a compound is always composed of the same elements in the same proportion by mass.
mass percentage of an element (%) = (mass of element / mass of compound) × 100%

1. a 20.0 - g sample of sucrose contains 8.4 g of carbon. what is the mass percentage of carbon in sucrose? show your work.

Explanation:

Step1: Recall element - compound definitions

An element is a substance that cannot be separated into simpler substances by physical or chemical means. A compound is a chemical combination of two or more different elements.

Step2: Answer multiple - choice questions

1. An element cannot be separated into simpler substances by physical or chemical means. So the answer is c.
2. A chemical combination of two or more different elements is a compound. So the answer is b.
3. Water ($H_2O$) is a compound, air is a mixture, sugar ($C_{12}H_{22}O_{11}$) is a compound, and oxygen ($O_2$) is an element. So the answer is d.
4. Gold, silver, and copper are elements, while aspirin ($C_9H_8O_4$) is a compound. So the answer is c.
5. The horizontal rows in the periodic table are called periods. So the answer is d.
6. The vertical columns in the periodic table are called groups or families. So the answer is b.

Step3: Label substances as element or compound

1. Silicon (Si) is an element.
2. Sodium chloride (NaCl) is a compound.
3. Francium (Fr) is an element.
4. Nickel (Ni) is an element.
5. Ice (solid $H_2O$) is a compound.

Step4: Write element symbols

1. Neon: Ne
2. Calcium: Ca
3. Iron: Fe
4. Titanium: Ti
5. Fluorine: F

Step5: Calculate mass percentage

1. Given mass of element (carbon) $m_{element}=8.4$ g and mass of compound (sucrose) $m_{compound}=20.0$ g.

Using the formula Mass percentage of an element $(\%)=\frac{mass\ of\ element}{mass\ of\ compound}\times 100\%$.
Substitute the values: $\frac{8.4}{20.0}\times 100\% = 42\%$.

Answer:

1. c. element
2. b. compound
3. d. oxygen
4. c. aspirin
5. d. periods
6. b. groups or families
7. element
8. compound
9. element
10. element
11. compound
12. Ne
13. Ca
14. Fe
15. Ti
16. F
17. 42%