[C4] Stoichiometry

Question 1

What does it mean if a reactant is in excess

Answer 1

There is more of it than needed to react with other reactants.

Question 2

What is a limiting reactant

Answer 2

The reactant that is used up first

Question 3

What are the steps for calculating reacting masses [5]

Answer 3

1. Identify the 2 substances in the equation
2. Write n,m,M underneath each one and hill in what you know
3. Calculate the number of moles for one of the substances
4. Consider stoichiometric ratios in the equation to calculate the number of moles of the other substances
5. Work out the mass/ volume for the substances in the question

Question 4

What is the equation that relates number of moles volume and concentration ?

Answer 4

Number of moles = volume * concentration

Question 5

What are the units for concentration

Answer 5

g/dm³ or mol/dm³

Question 6

How do you convert cm³ to dm³

Answer 6

1000cm³ = 1dm³

Question 7

Wat is the equation that relates number of moles, volume and molar gas volume

Answer 7

number of moles = volume / molar gas volume (24dm³ at RTP)

Question 8

What is the molar gas volume at RTP

Answer 8

The number of moles that a gas occupies at room temperature and pressure is 24dm³

Question 9

What equation relates number of moles mass and relative atomic mass

Answer 9

Number of moles = mass/relative atomic mass

Question 10

What is a mole

Answer 10

An amount of substances containing 6.02 * 10²³

Question 11

Define relative atomic mass [Aʳ]

Answer 11

The average mass of naturally occurring atoms of an element on a scale where the ¹²C atom has a mass of exactly 12 units

Question 12

What is the empirical formula of sodium oxide?

Answer 12

1. Establish what ions are formed by each component of the ionic compound.
   Na atom → Na+ ion.
   O atom → O2- ion.
2. Calculate the simplest ratio of these 2 ions that results in a net charge of zero.
   Na+ : O2- = 2 : 1.
3. Convert this ratio into a formula.
   Na2O.

Question 13

Calculate the relative formula mass (Mr) of magnesium carbonate (MgCO3).

Answer 13

Ar of Magnesium (Mg) = 24; Ar of Carbon (C) = 12; Ar of Oxygen (O) = 16

=84

Question 14

What happens when we electrolyse molten copper oxide (CuO)?

Answer 14

Positively charged copper ions (Cu2+) are attracted to the cathode.
A pinkish coat of copper will appear on the cathode.
Negatively charged oxygen ions (O2-) are attracted to the anode.
Oxygen atoms will form at the anode and combine to give O2 gas bubbles.