Chemical calculation

Chemical calculation

(A): Writing & Balancing Chemical Equations

(1): Sodium + Water \to Sodium hydroxide + Hydrogen gas

Step 1: Convert the word equation into a chemical equations by replacing all the reactants & products with their corresponding chemical symbols.

Na+H_{2}O \to NaOH+ H_{2}

Step 2: Balance the equation by ensuring the number of each type of atoms is the same on both sides of the equation.

2Na + 2H_{2}O \to 2NaOH + H_{2}

(2): Sodium chloride + Fluorine \to Sodium fluoride + Chlorine gas

NaCl + F_{2} \to NaF + Cl_{2} (Unbalanced)

2NaCl + F_{2} \to 2NaF + Cl_{2} (Final equation)

Practise Questions:

Write the chemical equations for the following equations:

(A): Calcium hydroxide + Hydrochloric acid ? Calcium chloride + water

(B): Sodium + Zinc fluoride ? Sodium fluoride + Zinc

(C): Iron + Copper (II) sulphate ? Copper + Iron (II) Sulphate

(D): C_{3}H_{6 }+ O_{2} ? CO_{2 }+ H_{2}O

(E): Ca(OH)_{2} + H_{2}SO4 ? CaSO_{4 } + H_{2}O

Relative Atomic Mass is the average mass of 1 atom of an element as compared with 1/12 of the mass of 1 atom of carbon-12 .

Relative Molecular Mass is the average mass of one molecule of the substance compared with 1/12 of the mass of 1 atom of carbon-12 .

Calculate the relative atomic mass & relative molecular mass of the following:

(i) Sodium Chloride

(ii) FeCl_{3} (Iron (III) chloride)

(iii) Na_{2}CO_{3} (Sodium carbonate)

(iv) CaF (Calcium fluoride)

The mole is defined as the amount of substance that contains as many particles (atoms/molecules/ions) as the number of carbon atoms, in 12 grams of Carbon-12.

12 grams of carbon atoms (1 mole of carbon) has a total of 6.0 X 10 23}atoms. Hence 1 mole of oxygen gas has a total of 6.0 X 10 23} oxygen molecules. 1 mole of water has a total of 6.0 X 10 23}water molecules. Questions: (1) Calculate the number of molecules in 2 moles of oxygen gas. (2) Calculate the number of moles of CaCl_{2}present in 18 X 10 23} molecules of CaCl_{2}.

(3) Calculate the number of hydrogen atoms present in 2 moles of water.

Molar mass

The mass in grams of 1 mole of a substance is called the molar mass .

mole = mass of sample molar mass

The molar mass of an element is the equivalent of relative atomic mass but with an unit (g).

Note: Relative atomic mass (or relative molecular mass) does not have units while molar mass has a unit of g/mol.

Questions:

(1) Calculate the mass of 2 moles of sulphur dioxide.

(2) Calculate the mass of 1.5 moles of oxygen gas.

(3) Calculate the number of moles present in 60g of hydrogen fluoride.

(4) Calculate the mass of 18 X 10 23}$ molecules of chlorine gas.

(5) Calculate the number of moles of oxygen atoms present in 2 moles of sulphur trioxide.

% Composition

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