Significant Figures Review



Significant Figures Review

Significant figure - _______________________________________________________

Rule 1

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i.e. 10, 1100, 120, 1000, 12500

Rule 2

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i.e. 10.0 3 sig figs

100.0 4 sig figs

Rule 3

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i.e. 25g, 0.025 kg, and 0.0025 mg all have two sig figs.

Rule 4

____________________________________________________________________________________________________________________________________________

i.e. 25.00g Typical lab balance (4 s.f.).

25.000 000g Highly precise microbalance (8 s.f.).

Examples:

How many sig figs in each measurement?

a. 3570

b. 17.505

c. 1.23400 x 108

d. 0.00900

e. 41.400

Math involving sig figs

After MULTIPLYING or DIVIDING numbers, round off the answer to the ____________________________________________ contained in the calculation.

For Example:

2.00 x 3.00000 = 6.00

3 s.f. 6 s.f. 3 s.f.

2.56x105 / 8.1x108 = 3.2x10-4

3 s.f. 2 s.f 2 s.f

After ADDING or SUBTRACTING numbers, round off the answer to the _________________________________________________________________.

ALWAYS perform calculations to the maximum number of sig figs allowed by your calculator.

Since the number with the least number of decimal places is the least precise, we would expect to round to this spot.

For Example:

12 .56 cm The second value is only precise

+125 .8 cm to the 1st decimal place, so the

138 .36 cm final answer is rounded to one

decimal place: 138.4 cm

**When adding/subtracting exponents, the exponents must be the same value

6.0 x 10^4 + 3.25 x 10^2

6.0 x 10^4 + 0.0325 x 10^4

Remember BEDMAS

Examples:

a. 14.34 x 34.678 =

b. 1.245 + 2.34 =

c. 34 / 7 =

d. 5.0 – 2.34 =

e. 365.0 x 2.34 x 50 =

f. 36 / 2.43 =

g. 4.567 + 1.2345 =

h. 25.00 x 0.1000 – 15.87 x 0.103

i. (4.63 x 8.054) + 11.7653

j. (0.341 x 18.64 -6.00) x 3.176

Mole Review

It’s important for you to remember that the mole is “central” to ALL conversions between mass, particles, and volume.

Each calculation goes from ______________ to ________ to ______________.

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Remember: ____________ is the mass of one mole of a substance and is equal to the atomic mass, or molecular mass, expressed in grams.

Examples:

a. What is the Molar Mass of Mg(OH)2?

b. How many grams in 2.9 mol of NaCl?

c. What is the volume occupied by 50.0 g of NH3(g) at STP?

d. What is the mass of 1.00x1012 atoms of Cl?

e. How many Oxygen atoms are contained in 75.0 L of SO3(g) at STP?

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