Chemistry Calculations & Equations

Question 1

What equation links mass, moles and relative atomic mass?

Answer 1

Mass (g) = Moles x Relative atomic mass (Mr)

Question 2

How can you calculate concentration in g/dm?

Answer 2

Concentration(g/dm3) = Mass(g)/Volume(dm3)

Question 3

What is the Avogadro constant?

Answer 3

The number of atoms, molecules or ions in one mole of a given substance.
The value of the constant is 6.02 × 1023.

Question 4

What formula links the Avogadro constant, moles and number of particles?

Answer 4

Number of particles = Avogadro constant x Moles

Question 5

How do you calculate Rf values?

Answer 5

Rf =Distance travelled by substance/Distance travelled by solvent

Question 6

What is the ionic equation for a neutralisation reaction?

Answer 6

H+ (aq) + OH- (aq) → H20 (l)

Question 7

What are the products when an acid reacts with a metal?

Answer 7

Salt and hydrogen
acid + metal → salt + hydrogen

Question 8

What are the products when an acid reacts with a metal oxide?

Answer 8

Salt and water
acid + metal oxide → salt + water

Question 9

What are the products when an acid reacts with a metal hydroxide?

Answer 9

Salt and water
acid + metal hydroxide → salt + water

Question 10

What are the products when an acid reacts with a metal carbonate?

Answer 10

Salt, water and carbon dioxide
Acid + metal carbonate→ salt + water + carbon dioxide

Question 11

Write the chemical equation for the reaction that occurs when calcium reacts with cold water?

Answer 11

Ca + 2H2O→ Ca(OH)2+ H2

Question 12

Write the chemical equation for the reaction that occurs when zinc reacts with steam?

Answer 12

Zn+ H2O→ ZnO +H2

Question 13

What is the chemical equation for the reduction of iron with carbon?

Answer 13

2Fe2O3 + 3C → 4Fe + 3CO2

Question 14

How can you convert concentration in g dm-3 to mol dm-3?

Answer 14

Concentration(mol dm-3) =concentration(g dm-3) ÷Mr

Mr - molecular mass

Question 15

How do you calculate percentage yield?

Answer 15

Percentage yield =
(Actual yield ÷ Theoretical yield) × 100

Question 16

How can atom economy be calculated?

Answer 16

Atom economy =(Mr of desired product ÷ Mr of reactants) x 100

Mr - molecular mass

Question 17

How can the molar volume of a gas be calculated? What are the units?

Answer 17

Molar volume = volume (dm^3) ÷ moles of gas

Question 18

How is the salt ammonium nitrate formed? Write a chemical equation for the reaction taking place?

Answer 18

React ammonia with nitric acid
NH3+ HNO3→ NH4NO3

Question 19

What is the chemical equation for the formation of ammonium sulfate from ammonia and sulfuric acid?

Answer 19

2NH3 + H2SO4 → (NH4)2 SO4

Question 20

Write an equation for the overall reaction that takes place in a hydrogen-oxygen fuel cell?

Answer 20

2H2 + O2 → 2H2O

Question 21

Write a balanced symbol equation for the reaction of sodium with water?

Answer 21

2Na + 2H2O→ 2NaOH + H2

Question 22

Write a balanced symbol equation for the reaction between bromine and sodium?

Answer 22

Br2+ 2Na → 2NaBr

Question 23

Write a balanced symbol equation for the reaction between chlorine and calcium?

Answer 23

Cl2+ Ca → CaCl2

Question 24

Write a word equation for the reaction between iodine and potassium?

Answer 24

lodine + potassium → Potassium iodide.
Remember: the ion of a halogen ends with -ide.

Question 25

What is the equation for rate of reaction?

Answer 25

Rate of reaction =Amount of reactant used or product formed/Time (s)

Question 26

How can the energy change of a reaction be calculated from bond energies?

Answer 26

Energy change (kJ mol) =Total energy of bonds broken - total energy of bonds made.

Question 27

What is the equation to calculate the surface area to volume ratio?

Answer 27

Surface area to volume ratio = Surface area ÷ Volume