Practice Quiz: Balancing Equations & Calculations

Sodium (Na) burns in oxygen (O₂) to form sodium oxide (Na₂O).

What is the balanced symbol equation for this reaction?

• 4Na + 2O -> 2Na₂O

• 4Na + O₂-> 2Na₂O

• 2Na₂ + O₂ -> 2Na₂O

• 2Na₂ + 2O -> 2Na₂O

Solid sodium metal (Na) reacts with water (H₂O) to form an aqueous solution of sodium hydroxide (NaOH) and hydrogen gas (H₂).

Which symbol equation is correct?

• 2Na_(s) + 2H₂O_(l) -> 2NaOH_(l) + H_2(g)

• 2Na_(s) + 2H₂O_(g) -> 2NaOH_(aq) + H_2(g)

• 2Na_(s) + 2H₂O_(l) -> 2NaOH_(aq) + H_2(g)

• 2Na_(s) + 2H₂O_(aq) -> 2NaOH_(aq) + H_2(g)

Germanium, Ge is extracted from Germanium(IV) oxide by heating with hydrogen.

Balance the symbol equation below for the reaction by writing the missing coefficient.

GeO₂ + _H₂ -> Ge + 2H₂O

Ethanol (CH₃CH₂OH) burns in oxygen (O₂) to form carbon dioxide (CO₂) and water (H₂O).

Which one shows the balanced symbol equation for this reaction?

• CH₃CH₂OH + O₂ -> CO₂ + H₂O

• CH₃CH₂OH + 2O₂ -> 2CO₂ + 3H₂O

• CH₃CH₂OH + 3O₂ -> 2CO₂ + 3H₂O

• CH₃CH₂OH + 5-> 2CO₂ + 6H₂O

Which of the following shows a balanced symbol equation for the reaction of nitrogen (N₂) and hydrogen (H₂) forming ammonia (NH₃)?

• N₂ + H₂ -> NH₃

• 2N₂ + 3H₂ -> 2NH₃

• N₂ + 2H₂ -> 2NH₃

• N₂ + 3H₂ -> 2NH₃

What is the relative formula mass (M_r) of Mg(OH)₂?

Calculate the relative formula mass (M_r) of ammonium phosphate, (NH₄)₃PO₄.

(A_r: N =14, H = 1, P = 31, O = 16)

Calculate the percentage composition by mass of nitrogen in ammonium phosphate, (NH₄)₃PO₄.

(A_r: N =14, H = 1, P = 31, O = 16)

Round off your answer to two significant figures.

(Example 1: 14.6 is rounded off to 15)

(Example 2: 12.1 is rounded off to 12)

Calculate the percentage composition by mass of Aluminium, (Al) in Aluminium oxide, Al₂O₃?

(A_r: Al = 27, O = 16).

Round off your answer to two significant figures.

• 26

• 53

• 54

• 63

Strontium carbonate, SrCO₃ is a compound used in red fireworks display.

Strontium is the element responsible for the red colour.

Calculate the percentage by mass of Strontium (Sr) in Strontium carbonate (SrCO₃)

Ar: Sr = 88, C = 12, O = 16

Round off your answer to two significant figures.

(Example 1: 14.6 is rounded off to 15)

(Example 2: 12.1 is rounded off to 12)