Mole concept

Question 1

Atomic, Molecular and formular mass

Answer 1

Atomic mass - mass of an atom (share the same value of molar mass (mass of mole substance ))

molecular mass - mass of an individual molecule (share the same value of molar mass (mass of mole substance ))

formula mass - mass of ionic compound

Question 2

molecular and empirical formula

Answer 2

molecular - types and no. of atoms in the molecule

empirical - simplest formulation - indicate mole ratio of element present in a compound

Question 3

Mole concept

Answer 3

large no. of atoms , molecules or ion to arrive at a measure able term for subatomic particles

Moles - amount of substance that contains as many elementary entities as they are in exactly 12g or carbon 12

moles : mass/ mm

moles : no. of particles / Na

Question 4

percentage composition by mass

Answer 4

list of percent by mass of each element in a compound :

calculated by

% mass of element = ((no. of atom in element x atomic mass of element ) / molecular formula mass of the compound ) x 100

Empirical formula can also be determined by percentage composition by mass :

• ensure all mass add up to 100
• find mole
• mole ratio

value of mole ratio will be value of the subscript in empirical formula

Question 5

chemical reaction , and some of the common chemicals reaction

Answer 5

• irreversible reaction, a reaction that proceed to completion

common chemicals reaction :

• combination (two or more reactant combine tgt )
• decomposition (breaking down of reactant to form more product )
• combustion ( burning substance containing C,H,O in oxygen to produce CO2 and H2O

Question 6

Combustion analysis

Answer 6

can be used for determining empirical formula

substance containing C,H,O ( or C,H - O is optional ) going thru combustion (reacting with O2 ) will form CO2 and H2O

Question 7

balance chemical equation and steps

Answer 7

based on law of conservation of mass :

• mass is neither created nor destroyed in ordinary chemical changes
• number of mole of atoms of each element must be the same on both sides of the equation

steps :

• write chemical formula for all reactant and product including state symbol
• identify most complicated compound
• select and balance the element that appear in only one reactant and product
• balance the remaining atoms of each kinds on both side
• fractional coefficient , to multiply both sides of the equation by denominator to make coefficient a whole number

Question 8

stoichiometry and coefficient and calculation

Answer 8

Stoichiometry shows the quantitative relationship of reactant and product using balanced chemical equation under the assumption of reaction is completed

stoichiometric coefficient is useful to establish mole ratio between reactant and product

in calculation, balance chemical equation are used to predict how much other reactant will be needed or product will be formed from a given amount of a certain reactant

Question 9

Limiting and excessive reagent

Answer 9

Limiting reactant : reactant that is used up first in a reaction, and there will be no product form after limiting reactant has been used up. the limiting reactant will also determine the amount of product that is produced

excessive reagent : reactant that is in greater quantity than necessary to react with the quantity of the limiting reactant . they are commonly supplied to ensure the more expensive or important reactant is convert completely to the desired product

consequences of : excess reactant getting left over at the end of the reaction

Question 10

percent yield

Answer 10

the percentage of the actual yield / theoretical yield

theoretical- stoichiometric amount of product form when all limiting reactant reacts to form desired product

actual yield - amount of product actually obtained from reaction ( this is usually lesser than theoretical yield due to some
reactant never react to form the desirable product , instead they form a diff product (side reaction ) or unreacted)

Question 11

percent purity

Answer 11

How pure a chemical is in the impure substance

%purity = (mass of pure in impure / mass of impure )x 100

Question 12

dissolution, types of solutions

Answer 12

dissolution - when solute place in contact with a solvent and dissolves to form a solution

Types of solution :
unsaturated - solute concentration is less than it’s solubility limit at specific temperature

saturated - solution concentration is at solubility limit at specific temperature

supersaturated - solute concentration is more than solubility limit at specific temperature. this solution is often unstable and crystal may be formed upon cooling

Question 13

concentration and it’s relative units

Answer 13

Concentration- ratio of the quantity of solute to the quantity of solution

units : 
molarity (temp dependent ) 
molality (temp independent ) 
%w/w 
%w/v 
%v/v 
ppm 
ppb 
normality : total reacting unit(H+,OH-,ionic salt)  x molarity

Question 14

Dilution

Answer 14

process to prepare a less concentrated solution from a more concentrated solution

Mc x Vc = Md x Vd

Question 15

diluting factor/ ratio

Answer 15

ratio of vulpine of diluted solution to volume of the less concentrated solution

DF = Vd/Vc

Question 16

Serial dilution

Answer 16

a series of dilutions that may used to prepare a number of increasingly dilute solution .

-the dilution factor remains constant for each dilution , resulting in exponential decrease in the concentration value

Question 17

solution stoichiometry and types of solution stoichiometry

Answer 17

Solution stoichiometry - ionic compound undergo complete dissociation upon dissolution and exist in solution ls entirely as ions

types of solution stoichiometry
- precipitate - two ionic compound form an insoluble ionic compound

Gravimetric analysis(quantitative method) - measurement of mass of ppt after isolation , this is highly accurate , but only applicable to reaction that can go to completion or 100% yield

• acid - base (titration, quantitative analysis ) - produce salt and H2O
  volume of standard solution and unknown solution used and concentration of standard solution we can calculate the concentration of unknown solution
• end point is the permanent colour change
• redox