CH. 2 SECTION 1-2 ANSWERS

WHAT ARE BASE UNITS?

They are defined units in a system of measurements.

A base unit is independent of other units.

PROVIDE THE SEVEN BASE UNITS OF SI. Seconds for time

Meters for length

Kilogram for mass

Kelvin for Temperature

Mole for Amount of substance

Ampere for electric current

Candela for luminous intensity

WHAT ARE DERIVED UNITS?

They are measurements that combines base units

Volume - cm3

Speed- m/s

Density- g/cm3

DEFINE DENSITY

Density is the ratio that compares the mass of an object to its volume. Density- g/cm3

1. A piece of matter with a mass of 147 g is placed in a 50 mL graduated cylinder. The water level rises from 20mL to 40 mL. What is the density of the metal?

Displacement of water from 20 to 40 gives us the volume of 20 mls.

Density = mass/volume

147g / 20ml = 7.35 g/ml

2. What is the volume of a sample that has a mass of 20 g and a density of 4g/mL?

So we are missing the volume D=m/x 4g = 20g 1ml Xml

Cross multiply and divide 4g xml = 20g/ml = 4g 4g

5 ml

3. A metal cube has a mass of 20 g and a volume of 5cm3. Is the cube made of pure aluminum? Explain you answer. See practice problem help.

Aluminum’s density is 2.7 g/ml 20g = 4 g/cm3

5 cm3

No, this is not pure aluminum

WHAT IS THE KELVIN SCALE, WHERE DOES CHEMISTRY USE THIS MEASUREMENT?

It’s the SI base unit of temperature where 273K is the freezing point of water and the boiling point of water is 373K

Kelvin is used in describing the behavior of gases.

CONVERT THE FOLLOWING

450 °C TO ___________K 25K___________°C

3°C TO _____________K 600K___________°C

0°C TO _____________K 0K___________°C

-60°C TO___________K 375K___________°C

*Celsius to Kelvin add 273*Kelvin to Celsius subtract 273

723

276

273

213

-248

327

-273

102

WHAT IS SCIENTIFIC NOTATION?

Scientific notation expresses numbers as multiple of two factors: A number between 1 and 10 And ten raise to a power, exponent

The exponent tells you how many times the first factor must be multiplied by ten. When numbers larger than 1

Power of 10 is in the positive When numbers smaller than 1

Power of 10 is in the negative

WHAT IS SCIENTIFIC NOTATION?

a. 700m

b. 38000m

c. 4500000m

d. 685000000000m

e. 0.0054kg

f. 0.00000687kg

g. 0.000000076 kg

h. 0.0000000008kg

7x 102 m

3.8 x 104 m

4.5 x 106 m

6.85 x 1011 m

5.4 x 10-3 kg

6.87 x 10-6 kg

7.6 x 10-8 kg

8 x 10-10 kg

WHAT IS THE RULE WHEN ADDING OR SUBTRACTING EXPONENTS?

When adding or subtracting numbers written in scientific notation, you must be sure that the exponents are the same before doing the arithmetic.

14. Read instructions and solve.

a. 5 X 10-5m + 2 X 10-5m = _____________________

b 7 X108m – 4X108m = _______________________

e. 1.26 X 104 kg + 2.5 X103kg __________________

g. 4.39 X 105kg – 2.8 X 104kg ___________________

7 x 10-5 m

3 x 108 m

Change exponents to be the same

12.6 x 103 kg

15.1 x 103 kg

1.51 x 104 kg

Change exponents to be the same

0.28 kg x 105 kg

4.11 x 105 kg

WHAT IS THE RULE WHEN MULTIPLYING OR DIVIDING EXPONENTS?

For multiplication, you multiply the first factors. Then, you add the exponents.

For division, you divide the first factors. Then, you subtract the exponent of the divisor from the exponent of the dividend.

15. Read instructions and solve.

a. 4 X 102cm x 1 X 108cm =

c. 3 X101 cm x 3 X10-2cm =

16b. 8 X 104 g ÷ 4 X101 cm3 =

d. 4 X 10-3g ÷ 2 X 10-2 cm3 =

4 x 1010 cm2

9 x 10-1 cm2

2 x 103 g/cm

2 x 10-1 g/cm

WHAT IS A CONVERSION FACTOR?

A conversion factor is a ratio of equivalent values used to express the same quantity in different units.

A conversion factor is always equal to 1.

19. HOW MANY SECONDS ARE THERE IN 24 HOURS?

24 hours

1 hour

60 minutes

Place starting amount here

--------

--------------

Place the units you want to get rid of across from each other

= 86,400 sec8.64 x 104 sec

Place conversion

factor here

Place conversion

factor here

1 minutes

60 seconds--------------

--------------

20. A CAR IS TRAVELING 90.0 KILOMETERS PER HOUR. WHAT IS ITS SPEED IN MILES PER MINUTE? ONE KILOMETER = 0.62 MILES.

90 km

1 km

0.62 miles

Place starting amount here

--------

-------------

Place the units you want to get rid of across from each other

= 0.93 miles/min9.3 x 10-1 miles/min

Place conversion

factor here

Place conversion

factor here

60 minutes

1 hour

--------------

-------------

1 hour

The Metric System

Base Units

Length meter

Mass gram

Time seconds

Prefix

kilo 1000hecta 100deca 10Base 1deci 0.1centi 0.01milli 0.001

Put in the prefix Prefix + base = measureme

ntmeterkilo- 1000 meters

liter

centi-

0.01 liters

deca- gram 10 grams

Conversions

Basedecahectakilo deci centi milli

300. centimeters = hm

Move the decimal point toward the prefix you want.

The decimal moved to the left 4 times

3000.03 hm 00

Practice

Basedecahectakilo deci centi milli

25 kilograms to _______________ decigrams

Where do we start?KiloWhere do we end?deciHow many spots and which direction?4 to the

right

250000

Practice

Basedecahectakilo deci centi milli

0.0043 grams to _______________ hectagrams

0.000043

38508 meters to _______________ kilometers1.34 milliliters to _______________ liters

975.6 liters to _______________ kiloliters

38.508

0.00134

0.9756

SCIENTIFIC NOTATION

Used to express really big or small numbers

Really big- power of 10 is in the positive

Really small- power of 10 is in the negative

You move the decimal point behind the first NON ZERO number.

PRACTICE

1392000 km Is this a big number or small? Is my power of 10 in the positive or

negative? Where does the decimal go? 1.392 x 106 km

PRACTICE SCIENTIFIC NOTATION

0.000003457 grams 3.457 x 10-6 grams48000 meters 4.8 x 104 meters0.0002563 meters 2.563 x 10-4 meters0.00000000967meters 9.67 x 10-9 meters8,900,000,000,000 kilometers8.9 x 1012 km

ADDING & SUBTRACTING SCIENTIFIC NOTATION

Make sure that the exponents are the same! 1.3 x 10-2 kg + 2.5 x 10-2 kg =

3.487 x 104 kg + 3.785 x 105 kg = Change them to match (doesn’t matter

which) 0.3487 x105kg + 3.785 x 105 kg =

3.8 x 10-2

kg

4.1337 x 105kg (is this correct??)4.134 x 105kg (is this correct??)

PRACTICE

5 x 10-5 m + 2 x 10-5 m =

1.26 x 104 kg + 2.5 x 103 kg =

7 x 10-5 m

1.5 x 104 kg

9 x 102 m -- 7 x 102 m =

2 x 102 m

5.36 x 10-1 km – 7.40 x 10-2 km =

4.62 x 10-1 km

MULTIPLYING SCIENTIFIC NOTATION

Multiply the factors first!! Then add the exponents Take care in assigning the sign to the

exponent Adding +3 to +4 = 7 but +3 to -4 = -1 Subtracting -6 from -4 = 2 but -4 from -6

= -2 (2 x 103 kg) X (3 x 102 kg) =

Rule 1 = 6 Rule 2 =1056 x 105 kg2

PRACTICE MULTIPLYING SCIENTIFIC NOTATION

4 x 1010 cm2(4 x 102 cm) (1 x 108 cm) =

9 x 10-1 cm2(3 x 101 cm) (3 x 10-2 cm) =

5 x 102 cm2(1 x 103 cm) (5 x 10-1 cm) =

DIVIDING SCIENTIFIC NOTATION

Divide the factors first!! Then subtract the exponent of the

divisor from exponent of the dividend (9 x 108 kg) ÷ (3 x 10-4 kg) = Rule 1: 9 ÷ 3 = 3 Rule 2: 8 - -4 = 12

3 x 1012 kg

PRACTICE DIVIDING SCIENTIFIC NOTATION

3 x 101 g(6 x 102 g) ÷ (2 x 101 g) =

3 x 106 cm(9 x 105 cm) (3 x 10-1 cm) =

2 x 10-1 cm(4 x 10-3 cm) (2 x 10-2 cm) =