4 Moles Flashcards
4.4 moles of iron are reacted with excess oxygen. How many moles of oxygen reacted?
Mole ration of Fe to O2 is 4 : 1
4.4 / 4 = 1.1 moles of oxygen reacts
The apparatus below is used to find the empirical formula of magnesium oxide.
2Mg + O2 –> 2MgO
- Measure the mass of the crucible + lid
- Add a coiled piece of magnesium metal
- Measure the mass of the crucible + lid + magnesium metal
- Heat the crucible using a roaring flame - be sure to lift the lid every minute and replace it
- When all the magnesium turns white, turn off the Bunsen burner and allow it to cool
- Measure the mass of the crucible + lid + Magnesium oxide.
- Repeat the heating and measuring the mass when cool until constant mass is reached.
How would the mass of oxygen be calculated from the data?
{Mass of crucible + lid + magnesium oxide} - {Mass of crucible + lid+ magnesium}
Below is the set up that can be used to work out the formula for the water of crystallisation of copper (II) sulfate.
What measurements must be taken to work out the ratio of CuSO4 to H2O at 1 :5?
- mass of evaporating basin
- mass of evaporating basin + hydrated copper sulfate - before heating
- mass of evaporating basin + anhydrous copper sulfate- after heating
The apparatus below is used to find the empirical formula of magnesium oxide.
2Mg + O2 –> 2MgO
- Measure the mass of the crucible + lid
- Add a coiled piece of magnesium metal
- Measure the mass of the crucible + lid + magnesium metal
- Heat the crucible using a roaring flame - be sure to lift the lid every minute and replace it
- When all the magnesium turns white, turn off the Bunsen burner and allow it to cool
- Measure the mass of the crucible + lid + Magnesium oxide.
- Repeat the heating and measuring the mass when cool until constant mass is reached.
Why is the heating repeated until constant mass is acheived?
To ensure all the magnesium has reacted
Below is the set up that can be used to work out the formula for the water of crystallisation of copper (II) sulfate.
The following measurements were taken:
- mass of evaporating basin
- mass of evaporating basin + hydrated copper sulfate - before heating
- mass of evaporating basin + anhydrous copper sulfate- after heating
Why must the crystals be heated until constant mass is reached?
To ensure that all the water has been removed- When all the water has been removed, the mass will no londer change.
How is molecular mass different from molar mass (relative formula mass)
Molecular mass is the relative mass of one molecule of a substance measure relative to carbon-12 just like realtive atomic mass is the relative mass of one atom of an element
However, molar mass or relative formula mass is the mass of one mole of that substance measured in g/mol.
Rearrange the equation to make mass the subject of the equation
mass = n x RFM
What does Mr stand for?
Relative molecular mass- mass of one molecule of a substance compared to 1/12th the mass of a carbon-12 atom and taking into consideration the abundance of the isotopes of the atoms the molecule is made of.
Below is an example calculation for the empirical formula of Fe2O3
List the steps taken to determine the empirical formula of a substance
- Calculate the moles of each element
- Divide by the smallest (1 : 1.5)
- multiply up to a whole number (2 : 3)
- Assign the ratio to show the empirical formula (Fe2O3)
What is a mole?
The measure of amount of substance
Below is the set up that can be used to work out the formula for the water of crystallisation of copper (II) sulfate.
The following measurements were taken:
- mass of evaporating basin
- mass of evaporating basin + hydrated copper sulfate - before heating
- mass of evaporating basin + anhydrous copper sulfate- after heating
How can you calculate the mass of water in hydrated copper sulfate?
mass of water = (mass of evaporating basin + hydrated copper sulfate) - (mass of evaporating basin + anydrous copper sulfate)
Below is the set up that can be used to work out the formula for the water of crystallisation of copper (II) sulfate.
The following measurements were taken:
- mass of evaporating basin
- mass of evaporating basin + hydrated copper sulfate - before heating
- mass of evaporating basin + anhydrous copper sulfate- after heating
Why must the crystals not be overheated?
To prevent the crystals from reacting and forming other products- only the water must to be removed- over heating may create dangerous fumes which should not be breathed in.
Below is the set up that can be used to work out the formula for the water of crystallisation of copper (II) sulfate.
The following measurements were taken:
- mass of evaporating basin
- mass of evaporating basin + hydrated copper sulfate - before heating
- mass of evaporating basin + anhydrous copper sulfate- after heating
How can you calculate the mass of copper sulfate in the sample?
mass of copper sulfate = (mass of evaporating basin + _anhydrous_ copper sulfate) - (mass of evaporating basin)
What equation links moles, mass and RFM?
What is the mole ratio of methane to chlorine ?
1 : 4
What is the mass of one mole of carbon?
12 grams
What is water of crystallisation?
It refers to the water molecules that form an essential part of a crystalline structure.
Eg. Copper sulfate has 5 water molecules bound to it
Define relative atomic mass (Ar)
The average mass of an atom relative to 1/12th the mass of a carbon-12 atom taking into consideration the abundance of its isotopes.
What is molar mass?
The molar mass is the relative formula mass (RFM) of a substance, measured in g/mol
What does the symbol Ar stand for?
Relative atomic mass - mass of one atom of an element compared to the 1/12th the mass of an atom of carbon-12 taking into consideration the abundance of its isotopes.
The apparatus below is used to find the empirical formula of magnesium oxide.
2Mg + O2 –> 2MgO
- Measure the mass of the crucible + lid
- Add a coiled piece of magnesium metal
- Measure the mass of the crucible + lid + magnesium metal
- Heat the crucible using a roaring flame - be sure to lift the lid every minute and replace it
- When all the magnesium turns white, turn off the Bunsen burner and allow it to cool
- Measure the mass of the crucible + lid + Magnesium oxide.
- Repeat the heating and measuring the mass when cool until constant mass is reached.
How would the mass of magnesium be calculated from the data?
{Mass of crucible + lid + magnesium} - {Mass of crucible + lid}= mass of magnesium
To find the formula for hydrated crystals such as hydrated copper sulfate the following steps are taken to find the ratio of CuSO4 to H2O:
- Calculate the mass of anhydrous crystal AND mass of water from the experimental data
- Calculate the number of moles of each by dividing mass by the RFM
What are the last two steps?
- divide both by the smallest moles value to find the ratio (e.g. 1 : 5)
- assign the empirical formula (e.g. CuSO4 •5H2O)
Find the molecular formula of a substance with a relative formula mass of 87 and an empirical formula of C2H5
RFM of C2H5 = 12+12+1+1+1+1+1=29
87/29 = 3
molecular formula is (C2H5)x 3 = C6H15
What is an empirical formula?
the simplest whole number ration of atoms in a substance
Below is an example calculation to find mass of a substance produced in a reaction.
List the steps you take to complete this calculation
The apparatus below is used to find the empirical formula of magnesium oxide.
2Mg + O2 –> 2MgO
- Measure the mass of the crucible + lid
- Add a coiled piece of magnesium metal
- Measure the mass of the crucible + lid + magnesium metal
- Heat the crucible using a roaring flame - be sure to lift the lid every minute
- When all the magnesium turns white, turn off the Bunsen burner and allow it to cool
- Measure the mass of the crucible + lid + Magnesium oxide.
- Repeat the heating and measuring the mass when cool until constant mass is reached.
Why is the magnesium coiled?
The magnesium is loosely coiled to give the magnesium a large surface area and ensure all the magnesium reacts with the oxygen.
The apparatus below is used to find the empirical formula of magnesium oxide.
2Mg + O2 –> 2MgO
- Measure the mass of the crucible + lid
- Add a coiled piece of magnesium metal
- Measure the mass of the crucible + lid + magnesium metal
- Heat the crucible using a roaring flame - be sure to lift the lid every minute and replace it
- When all the magnesium turns white, turn off the Bunsen burner and allow it to cool
- Measure the mass of the crucible + lid + Magnesium oxide.
- Repeat the heating and measuring the mass when cool until constant mass is reached.
What are the possible inaccuracies in this method?
- The magnesium ribbon is impure magnesium
- The magnesium ribbon has an oxide layer at the start
- The magnesium ribbon has not fully reacted- some magnesium at the centre of the ribbon is not exposed to oxygen, lid not lifted enough
- Experiment was not repeated until constant mass was achieved.
If 0.2 moles of methane reacted with excess chlorine, how many moles of hydrogen chloride would be produced?
1 : 4 mole ratio
0.2 x 4 = 0.8 moles of hydrogen chloride would be produced.
How do you find the empirical formula of a substance if you were given the percentage by mass of atoms in the substance?
- Assume 100g of substance
- Calculate the moles of each element
- Divide by the smallest to get the ratio
- Multiply up to get whole number
How many moles of H2O would be produced if 0.25 mol of O2 was reacted with excess hydrogen?
1 : 2 mole ratio
0.25 x 2 = 0.5 mol
Therefore 0.5 mol of H2O would be produced
How many molecules are there in 2 moles of oxygen?
2 x 6.03 x 1023 molecules
OR 12.6 x 1023 molecules
Show that the RAM of chlorine is 35.5, if a sample of chlorine contains 75% Cl-35 and 25% Cl-37.
[0.75 x 35] + [0.25 x 37] = 26.25 + 9.25 = 35.5
The apparatus below is used to find the empirical formula of magnesium oxide.
2Mg + O2 –> 2MgO
- Measure the mass of the crucible + lid
- Add a coiled piece of magnesium metal
- Measure the mass of the crucible + lid + magnesium metal
- Heat the crucible using a roaring flame - be sure to lift the lid every minute
- When all the magnesium turns white, turn off the Bunsen burner and allow it to cool
- Measure the mass of the crucible + lid + Magnesium oxide.
- Repeat the heating and measuring the mass when cool until constant mass is reached.
Why is the lid lifted every minute during the heating process?
To allow oxygen in to react with the magnesium- this ensures that all the magnesium has reacted.
4.4 moles of iron are reacted with excess oxygen. How many moles of iron oxide are made?
Mole ration of Fe to Fe2O3 is 4 : 2 or 2 : 1
4.4 /2 = 2.2 moles of Fe2O3 are made
What is the mass of 2 moles of carbon?
2 x 12 g/mol = 24 g
What is a molecular formula?
The number of atoms in a substance
How many moles of H2O would be produced if 0.5 mol of H2 was reacted with excess oxygen?
2:2 mole ratio
Therefore 0.5 mol of H2O would be produced
The apparatus below is used to find the empirical formula of magnesium oxide.
2Mg + O2 –> 2MgO
- Measure the mass of the crucible + lid
- Add a coiled piece of magnesium metal
- Measure the mass of the crucible + lid + magnesium metal
- Heat the crucible using a roaring flame - be sure to lift the lid every minute and replace it
- When all the magnesium turns white, turn off the Bunsen burner and allow it to cool
- Measure the mass of the crucible + lid + Magnesium oxide.
- Repeat the heating and measuring the mass when cool until constant mass is reached.
Why is the lid replaced after lifting each time?
To ensure that no product is lost
If 4.2 moles of methane reacted with excess chlorine, how many moles of tetrachloro methane would be produced?
1 : 1
4.2 moles of tetrachloromethane would be produced
What does the empirical formula MgO tell you about the compound?
MgO
There is 1 atom of Mg for every 1 atom of oxygen
In MgO there are 1 mole of Mg atoms for every 1 mole of O atoms.
What is the mole ratio of O2 to H2O
1 : 2 mole ratio
How many atoms are there in a mole of substance?
6.02 x 1023 atoms
This is called Avogadro’s number
