Matter and Measurement

Evidence of chemical change

Color change, heat, light, precipitate formation, and gas formation

Phase changes are…

physical changes

Elements

substances that cannot be decomposed into simpler substances (one kind of atom)

Compound

composed of two or more elements; \**two or more* ***kinds*** *of atoms**

Mixtures

combinations of two or more substances in which each substance retains its chemical identity

Examples of homogeneous mixtures

saltwater, coffee, bronze

Examples of heterogeneous mixtures

granite, sand, oil and water, italian dressing, wood

Extensive properties

depends on the amount of sample; mass and volume

Distillation

a process that depends on the different abilities of substances to form gasses; boiling salt water, leaving the salt behind

Chromatography

the differing abilities of substances to adhere to the surfaces of solids can also be used to separate mixtures

Precision

measure of how close individual measurements are with one another (determined by standard deviation)

Accuracy

how closely individual measurements agree with the correct, or “true,” or expected value

There is always uncertainty in the…

last digit of any measured quantity (the uncertain one is also significant)

The final answer should be reported with only ___ uncertain digit

1

What difference exists between 4.0g and 4.00g

4\.0 only has 2 sig figs, so it has MORE uncertainty

Zeros between nonzero digits are…

always significant

Zeros at the beginning of a number are…

never significant

Zeros at the end of a number are…

significant if the number contains a **decimal** point (0.0200g has 3 sig figs)

When a number ends with zeros but contains no decimal point, the zeros are…

not significant

Exponential terms are…

not significant

Sig fig addition/subtraction

the result has the same number of decimal places as the measurement with the **fewest decimal places**

Sig fig multiplication/division

the result contains the same number of sig figs as the measurement with the **fewest number of sig figs**

Sig fig rounding

• If the leftmost digit removed is less than 5, the preceding number is left unchanged (7.248 rounded to 2 sig figs is 7.2)

• If the leftmost digit removed is 5 or greater, the preceding number is increased by 1 (4.735 rounded to 3 sig figs is 4.74)

Intermediate value rules

**don’t round intermediate values**, but remember the number of sig figs it should have, and apply that number of sig figs to the final calculation

Density =

m/v (it can be used a conversion factor)