Quantiative Chemistry

Question 1

How to find percentage by mass

Answer 1

Relative atomic mass of element
% mass of element=————————————————— x100
Relative formula of compound

Question 2

Reactant and peoducts are _______

How can mass of reactants be greater then products or less

Answer 2

Balanced

Products may be lost during a reaction (gas of mass of a substances diffuses away). Mass of reactants greater then products. Impurities in reactants or reaction vessels create unexpected products. Mass of products greater then reactants used

If the mass increases the reactants are gas and the products are (s,l,aq). Gas floats in reaction vessel but not accounted for. Gas reacts to form product inside the reaction vessel mass increases inside.

Question 3

How to balance an equation

Answer 3

Make sure each elements in the reactant and products have the same amount of molecules

Question 4

What is 1 mole equal to (Avogadro’s constant)

Answer 4

6.022x10^23

Question 5

What is a mole of a substance equal to

Answer 5

The Relative atomic mass

Question 6

Equation of mole of substance

Answer 6

Mass of substance in grams
Mol=—————————————————
Relative mass of substance (Mr)

Question 7

How to calculate concentration

Answer 7

Moles of solute or
Mass of solute in solution (g)
Concentration=———————————————-
Volume of solvent (dm)

Question 8

How to convert cm^3 to dm^3

Answer 8

Volume in cm^3
Volume in d^3=—————————-
1000

Question 9

Solute, solvent, soluble, insoluble defs

Answer 9

1. Solute: The solid substance which is dissolved in a solution
2. Solvent: The liquid in which a substance is dissolved to form a solution
3. Soluble: A compound that can be dissolved in a given solution
4. Insoluble: A solution that can’t be dissolved in a given solution

Question 10

How to calculate mass of products formed in a reaction by using the mass of the limiting reactant and balanced equation

Calcuate mass of aluminium oxide formed when 135g of aluminium is burned in the air?

Answer 10

1) write the balanced equation 4Al + 3O2 -> 2Al2O3

2) Find the (Mr) of reactants and product Al=27 x 2 + 3 x 16 = 102

                                                                                     135g 3) Number of moles in mass substance Al=135g -------------=5
                                                                                      27

4) Calcuate ratio of mole in equation 4mol AL = 2 mol Al2O3 —> 5mol Al =2.5mol Al2O3

5) Calcuate mass of 2.5 mole of aluminium oxide mass=mole x Mr = 2.5 x 102=255g

Question 11

Calculating gas volumes from equations

Answer 11

Hcl(aq)+ NaHCO3(s) -> NaCl(s) + H2O(l) + Co2(g)

Hcl and NaHCO3 to CO2 is 1:1

If we know the mass of either we can calculate the volume of Co2 evolved

Question 12

Calculation for relationship between volume and moles

Answer 12

Volum of gas at 20°c and 1 atm = 24 X Moles of gas present