mass
'no magic to the mole'
amount
molar mass
concentration
solution volume
gas volume
molar gas volume
Avogadro
constant, L
number of
entities, N
Now try the following question.
C2. CALCULATING AN AMOUNT BY WEIGHING
Coins can be counted by weighing them. If the cashier in a bank is given a bag containing 20 p coins they would not waste time counting them to ascertain the total value but rather, by measuring the total mass and knowing the mass of an individual 20 p coin, they could calculate the total number of coins and hence their value (in practice a calibrated machine does the donkey work).
Suppose a bag containing 20 p UK coins is found to have a mass of 356 g and an individual coin is known to have a mass of 7.12 g. It follows that the bag contains 50 coins.
For m = 178 g, there must be 25 coins present.
The general relationship used between the quantities in these calculations is the expression
The term ‘unit amount’ refers to the counting unit being adopted, e.g., one pair, one dozen, one ream, etc., as in shoes, eggs, paper.
Re-write a relationship similar to that above in order to solve the problem that follows.
Q. One dozen chocolate biscuits has a mass of 180 g.
Calculate the amount (unit: dozen) of chocolate biscuits in a batch of mass 5760 g.