Chemistry - Chapter 2 Measurements and Calculations

Model

Explanation of how phenomena occur. Not real.

Theory

Broad generalization that explains a body of facts or phenomena

Hypothesis

educated guess of the cause of the problem or answer to the question.

Experiment

designed to test the hypothesis

Which stages of scientific method involve data?

all

What might be wrong if repeated tests don’t support hypothesis?

hypothesis might be wrong

Two parts of a metric system:

A prefix and a base unit

what does a prefix tell you?

how many times to divide or multiply by 10.

In SI measurment, dont use what?

Don’t use commas because this means a \n decimal point in some countries. Use a space instead. 75,000 is written as 75 000. (with a space)

deci d =

1/10 (10 to the -1)

centi c =

1/100 (10 to the -2)

milli m

1/1000 (10 to the -3)

micro μ

10 to the -6

a derived unit

the properties of base unit ( cm squared, square unit)

In a beaker, there are 8 different substances which substance is denser?

the one on the bottom (its heavier)

What state of matter is mercury?

liquid

What state of matter is ice?

solid

D = mass/volume can be simplified to

g/ml or g/cm 3 (cubed) Note: 1 mL = 1 cm 3 (cubed)

What is the density of osmium if 50g of the metal occupies a volume of 2.22cm 3 cubed?

22\.5 g/cm3

8 cm 3 (cubed) =

8 mL

48g/8mL to density (g/cm3)?

6 g/cm3

Water freezes at what temp?

0 C

Celsius formula

C = K - 273

Kelvin formula

K = C + 273

Dimensional Analysis

a **method of analysis in which physical quantities are expressed in terms of their fundamental dimensions of length, mass, and time**

How many m 3 (subed is 1500 cm 3 (cubed)

0\.0015m 3 (cubed)

6 ft =

1 fathom

Accuracy

how close the measurement is to the actual value

Precision

how well can the measurement be repeated

How many sig figs in 12400?

3

How many sig figs in 0.045?

2

How many sig figs in 3440. cm?

4

How many sig figs in 0.006 700 0 kg?

5

Do measurements have sig figs?

Yes, Only measurements have sig figs

Counted numbers

exact (infinite significance)

ex: a dozen donuts, a paper measured 11 inches

Is gold melting at 1064°C exact or measured?

measured

Is 1 yard = 3 ft exact or measured?

exact

How many sig figs in 250 pencils

Infinite because its counted

Round 45.462 to four sig figs

45\.46

Round 45.462 to three sig figs

45\.5

Round 45.462 to two sig figs

45

Round 45.462 to one sig fig

50

If rounding from a “final 5”, then round to an

even number

Round 78.65 to 3 sig figs

Rounds down to 78.6 (even number)

Round 78.75 to 3 sig figs

Rounds up to 78.8 (because its an even number)

Round 4.652 to 2 sig figs

4\.7 (its not a final 5)

When add/subtracting sig figs,

The # with the lowest decimals value determines the place of the last sig fig in the answer

27\.93 + 6.4 (sig figs)

34\.3

When mult/diving sig figs,

the # with the lowest sig figs determines the answers amount of sig figs

3\.6 x 653

2400 (rounded

4\.5/6.245

0\.72

9\.8764 x .043

0\.42

Problem solving step 1

\
Analyze: Identify the unknown

\

Problem solving step 2

Plan a solution

The “heart” of problem solving

Break it down into steps.

Look up needed information

Problem solving step 3

Compute (calculate) - cancel units, sig figs

Problem solving step 4

Evaluate-

Sig Figs correct,

Units correct,

Check your work,

Reread the question, did you answer it,

Is it reasonable? Estimate (check order of magnitude)

Direct proportions formula

y/x=k or y=kx

Indirect proportions formula

xy=k

In sig figs if there is a 5, round up only if

the number before the 5 is odd

In sig figs if there is a 5, let the number be (dont round up) only if

the number before the 5 is even

Convert 31.95 x 10^3kg to Scientific Notation

3\.195 x 10^4

Convert 500,000 cm 3 (cubed) → m3 (cubed)

0\.5 cm 3

Convert 2.4 x 10 to the 8th cm 3 (cubed) → m 3 (cubed)

2\.4 x 10 to the 2nd m 3 (cubed)

Convert 8.92m 3 (cubed) in cm 3 (cubed)

8,920,000 cm 3 (cubed)