Unit 1 - Reaction Quantities

Question 1

What is meant by the gram formula mass (GFM) of a substance?

Answer 1

The GFM is the mass of one mole of a substance.

Question 2

How do you calculate the Gram Formula Mass (GFM) of a compound?

Answer 2

Work out the formula then add all the mass numbers for the atoms in the compound together.

Question 3

What is the GFM of Carbon Dioxide?

Answer 3

CO2

12 + (2x16) = 44

Question 4

To calculate the mass of a number of moles an equation is used - what is the equation?

Answer 4

mass = moles x gram formula mass

Question 5

How many moles are present in 25 g of calcium carbonate? (GFM=100)

Answer 5

number of moles = mass/GFM

25/100 = 0.25 moles

Question 6

Calculate the mass of 0.25 moles of butane (C4H10)

Answer 6

mass = number of moles x GFM

mass = 0.25 x 58

mass = 14.5g

Question 7

If the number of moles of solute and the volume of solvent used is known, the concentration of the solution can be calculated. What equation is used?

Answer 7

Concentration = moles / Volume (in litres!)

Question 8

How many of moles in 400cm3 of 0.2 mol l-1 sodium hydroxide (NaOH) solution.

Answer 8

Number of moles = concentration x volume

Convert volume to litres by dividing by 1000

= 0.2 x 0.4

= 0.08 moles

Question 9

Calculate the concentration of the solution formed when 0.75 moles of sodium chloride are dissolved in 500 cm3 of water.

Answer 9

Concentration = number of moles/volume.

Convert volume into litres by dividing by 1000.

Concentration = 0.75/0.5

Concentration = 1.5 mol l-1

Question 10

Calculate the volume of sodium hydroxide used in 0.6 mol l-1 solution containing 1.2 mol of solute.

Answer 10

Volume = number of moles / concentration

= 1.2 / 0.6

= 2 litres

Question 11

Equations can be described as being balanced. What does this mean?

Answer 11

A chemical equation is said to be balanced when there are the same number of the same type of every atom on both sides of the equation.

Question 12

How can you balance an equation?

Answer 12

Balancing is adding BIG numbers. You cannot change any of the small numbers in a chemical formula. If balancing is required, put the number in front of the substance.

Question 13

How would this equation be balanced?

Cu + O2→ CuO

Answer 13

2Cu + O2 →​ 2CuO

Question 14

Balance this equation

C4H8 + O2 → CO2 + H2O

Answer 14

Balance Carbons

C4H8 + O2 → 4CO2 + H2O

Balance Hydrogens

C4H8 + O2 → 4CO2 + 4H2O

Balance Oxygens

C4H8 + 6O2 → 4CO2 + 4H2O