Accuracy and Precision

In this class, for those of the people in physics, we reviewed accuracy and precision followed by significant digits.

Precision - how reproducible a measurement is compared to other similar measurements

EG: bounces of a basketball on one spot

Accuracy - how close the measure(or average measurement) comes to the accepted or real value.

EG: 2 + 2 = 4 (not 4.1 or 4.2 etc)

SIGNIFICANT FIGURES


-measured or meaningful digits
-more precise = more significant digits
-The last digit is considered uncertain(it could be one digit higher or lower).
-Includes all certain digits and the first uncertain****

Note: Leading 0's are not counted

EG: 0.00000000005 <--- only one significant digit
-Trailing 0's are counted

EG: 10.9029000
-If there is a decimal, count the zero as a significant digit.


EG: 100000.

EXACT NUMBERS


-Some quantities are defined exactly a certain amount and no rounding is required
-Exact numbers have an infinite amount of sig figs.


ROUNDING RULES


1) Look at the digit after the position of rounding
2) If >5 round up
3) If <5 keep it the same
4) If = 5 and more non-zero digits, round up
5) If = 5 and ends at five, round to make it even.

MATH RULES FOR SIG FIGS


-When adding or subtracting, round to the fewest number of decimals.
-When multiplying or dividing, round to the fewest number of sig figs.

MULTIPLYING AND DIVIDING

- When multiplying and or dividing, round to the fewest number of sig figs

E.g. 12.54 x 1.3 = 16.302 <-- you must round that to 16.30.

12.540/1.3 = 9.64 <-- you must round to 2 sig figs (2<4) or the first uncertain digit.

Chromatography Lab

During a lab, remember to follow the rules and also be safe!

1. In this lab, we've observed how chromatography works.
2. By putting a blob of food colouring on the strip of chromatography paper and placing it in water, one could observe the different colours that make up the original food colouring.
3. After observing, we measured the distance between the solvent(d1) and the solute(d2) and got the Rf value.

• The Rf value is d1/d2.
• The Rf value cannot be less than 0 or greater than 1.

Naming/Writing Ionic , Covalent , Acidic Compound

Ionic Compound:

Ionic compounds are formed when a metal gives up its electrons to a non-metal. So , to name the ionic compound we apply these rules :

The metal ion's name + the non-metal's name ends in ide.

Ex:

AlCl₃ = aluminum chloride

Na₂S = sodium sulfide

K₂O = potassium oxide

MgH₂ = magnesium hydride

Way to write the formula of an ionic compound

We have to make sure that the sum of charges = 0

Ex: Ca⁺² and P^-3

One of each would create a sum of 2 + (-3) = -1. To get a sum of zero, we need three Ca⁺² ions and two P^-3 for a total of 3(2)+ 2(-3) = 0.

So the answer is Ca₃P₂

Polyatomic Ions

Polyatomic Ion	Name
OH-1	hydroxide
SO4-2	sulfate
PO4-3	phosphate
NO3-1	nitrate
CO3-2	carbonate
HCO3-1	hydrogen carbonate or bicarbonate
ClO3-1	chlorate
NH4+1	ammonium

Ionic Compounds formed by a metal which has more than one charge

We apply this rules :

Metal element's name + ( charge in roman number ) + name of non-metal element + ide

Example:

Cu₂O = Copper (I) oxide

CrCl₃ = chromium (III) chloride

Covalent Compound: These are formed from non-metals that share electrons.

We apply these rules:

Prefix + First element's name + Prefix + Second element with “ide " ending.

For this we use a set of prefixes:

mono di tri tetra penta hexa hepta octa nona deca

1 2 3 4 5 6 7 8 9 10

Examples: CO = carbon monoxide (note we don't say monocarbon monoxide)

CO₂ = carbon dioxide

N₂O₅ = dinitrogen pentoxide

PCl₃ = phosphorus trichloride

Acid :

1. Naming the simple acid :

Hydro + name of the second element with “ ic “ in the end + acid

Ex: HCl = Hydrochloride acid

HBr = Hydrobromide acid

2. Naming the complex acid :

- Change the suffix of the polyatomic ion:

If the suffix is ate, change to “ic “

If the suffix is ide, change to “ous “

- Add acid in the end

Ex:

H2SO4 : sulphuric acid

HClO4 : perchloric acid

H2SO3 : sulphurous acid