# Retake Criteria for Unit 4 Assessment 2014 ## Measurements

### Using and Expressing Measurements (section 3.1)

You must…

1.

Complete the extra Section 3.1 WS attached below (scroll down) and check answer key posted in the room

2.

Meet with your teacher and go over this section before retaking.

### Units of Measurement - Density (section 3.2)

You must…

1.

Complete the extra Section 3.2 WS attached below (scroll down) and check answer key posted in the room

2.

Meet with your teacher and go over this section before retaking.

Name Class Date

# Scientific Measurement

Section 3.1

### Using and Expressing Measurements

Essential

Understanding

In science, measurements must be accurate, precise, and written to the correct number of significant figures.

### Scientific Notation

Scientific notation is a kind of shorthand to write very large or very small numbers.

Scientific notation always takes the form (a number ≥ 1 and < 10) × 10

x

.

### Scientific Notation

1.

Why are numbers used in chemistry often expressed in scientific notation?

2.

Circle the letter of the answer in which 503,000,000 molecules is written correctly in scientific notation.

a.

5.03 × 10

−7 molecules

c.

5.03 × 10

8

molecules

b.

503 × 10

6 molecules

d.

503 million molecules

3. Write the following numbers in scientific notation.

2901000000 kg

0.000000510270 mL

300.70 °C

4. Write the following scientific numbers in “normal” numbers.

3.00 x 10

-8

nm

5.210 x 10

3

K

1.097 x 10

15 atoms

_________________________

_________________________

_________________________

_________________________

_________________________

_________________________

### Percent Error

5.

The theoretical value of a measurement is 200 cm, but in the lab, a student measured it to be 198 cm.

Circle the letter of the value that shows the percent error of this measurement.

a.

2%

b. −

2%

c.

1%

d. −

1%

6.

If a student determines the density of aluminum to be 2.97 g/mL and the accepted density value is

2.70 g/cm

3

, what is this student’s percent error?

### Significant Figures

Significant figures include all known digits plus one estimated digit.

The number of significant figures reflects the precision of reported data.

In calculations, the number of significant figures in the least precise measurement is the number of significant figures in the answer.

Significant Figures

Sample number: 0.024050 (5 significant figures)

Not significant

Significant leftmost zeros in front of nonzero digits: a nonzero digit: 0.0

24

0

5

0

0.0

24050 zeros between two nonzero digits: 0.02

40

50 zeros at the end of a number to the right of the decimal point:

0.02405

0

### Significant Figures

7. How many significant figures are in each of the following numbers? a) b)

5.40 ____

210 ____ f) g)

1.8 x 10

3

____

0.00190 ____ c) d) e)

801.5 ____

1,000 ____ h) i)

0.0112 ____

9.010 x 10

-6

____

401.0800 ____ j) 2,370.0 ____

8. Why are significant figures important when taking data in the laboratory?

9) Why are significant figures NOT important when solving problems in your math class?

10. Round the following measurements as indicated. a.

Round 65.145 meters to 4 significant figures.

b.

Round 100.1°C to 1 significant figure.

c.

Round 155 mg to 2 significant figures.

d.

Round 0.000718 kilograms to 2 significant figures.

e.

Round 85.152 Liters to 3 significant figures.

______________________________

______________________________

______________________________

______________________________

______________________________

### Significant Figure Calculations

Solve the following mathematical problems such that the answers have the correct units and correct

13)

14)

12)

number of significant figures:

34 grams / 10.1 mL = 11)

2.61 x 10

6

___________________

joules / 0.0034 seconds = ___________________

349.0 cm x 1.10 cm x 100. cm =

44 m/s x 20 s =

___________________

___________________

Name

# Scientific Measurement

Class

Section 3.2

### Density

Density is a ratio that compares the amount of mass per unit volume. mass

The formula for density is density = volume

.

Density depends on the kind of material but not on the size of the sample.

The density of a substance changes with temperature.

Date

1.

Mass

2.85 g

Volume Density

0.767 g/cm

3

2. 12.05 mL 10.63 g/mL

3. Mercury metal is poured into a graduated cylinder that holds exactly 22.5 mL. The mercury used to fill the cylinder weighs 306.0 g. From this information, calculate the density of mercury.

4. What is the mass of the ethyl alcohol that exactly fills a 200.0 mL container? The density of ethyl alcohol is 0.789 g/mL.

5. A rectangular block of copper metal weighs 1896 g. The dimensions of the block are 8.4 cm by 5.5 cm by 4.6 cm. From this data, what is the density of copper?

6. A block of lead has dimensions of 4.50 cm by 5.20 cm by 6.00 cm. What is the mass of this lead block? (density of lead is 11.34 g/cm

3

)

7. A sample containing 28.5 g of iron shot is added to a graduated cylinder containing 45.50 mL of water. The water level rises to the 49.10 mL mark, from this information, calculate the density of iron.

8. What volume of silver metal will weigh exactly 2500.0 g. The density of silver is 10.5 g/cm

3

.

9. A furniture maker wants to determine if two pieces of wood are of the same type and determines to find the densities of each. The first piece of wood is 30 cm x 14 cm x 2.5 cm and weighs 350 grams. The second piece of wood is 15 cm x 15cm x 10 cm and weighs 900 grams. Are they different types of wood? Explain with words and calculations.

10. If a graduated cylinder initially held 25.0 mL of water and then a 37.81 g piece of iron was placed into it, what would be the final volume reading of the graduated cylinder? What was the volume of just the piece of iron?