Transcript Practice questions Module 1

Practice questions
Module 1
Basic skills
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Mr and moles to grams
Grams and moles to Mr
Mr and grams to moles
Concentration and volume to moles
Concentration and moles to volume
Volume and moles to concentration
Read equation, use it to calulate moles
Gas equation – derive any one value from the
others by changing subject and substituting in.
e.g. 1 What will you do?
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HCl + NaOH  NaCl + H2O
500 ml of acid was spilt. 670ml of 1 molar alkali
was needed to neutralise it, so what was the
concentration of the original acid?
Suggested steps:
Moles of alkali from volume in dm3 x
concentration
Equation shows this equals moles of acid
Find concentration from volume and moles
If you’re clever you can do it in one go. I don’t.
e.g. 2 What will you do?
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H2SO4 + 2NaOH  Na2SO4 + H2O
180 ml of alkali was spilt. 275ml of 0.25 molar
acid was needed to neutralise it, so what was
the concentration of the original alkali?
• Suggested steps:
1. Moles of acid from concentration x volume
(don’t forget this needs to be in dm3)
2. Equation shows this equals half the moles of
alkali so double it
3. Find concentration from volume and moles
e.g. 3 What will you do?
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H2SO4 + Na2CO3  Na2SO4 + H2O + CO2
210g of sodium carbonate was reacted with an
excess of 0.5 molar acid. What volume of
carbon dioxide was evolved (assume 298K and
101kPa, R=8.31)?
Likely steps:
Moles of carbonate from mass and Mr
Equation shows this equals the moles of CO2
Could use 24 litres per mol or use ideal gas
equation
Change subject of ideal gas equation
Use IG equation to find volume of this many
moles of gas.
e.g. 4 What will you do?
• H2SO4 + 2NaHCO3  Na2SO4 + 2H2O + 2CO2
• 4.90g of sodium hydrogencarbonate was
reacted with an excess of acid. What volume of
carbon dioxide was evolved?
• Likely steps:
1. Moles of carbonate from mass and Mr
2. Equation shows this equals the moles of CO2
3. Multiply moles by 24 dm3 to find volume of this
many moles of gas.
e.g. 5 What will you do?
• 2H2(g) + O2(g)  2H2O(g)
• 1.2 dm3 of hydrogen was placed in a
balloon at 110kPa and 293K and ignited.
What mass of water vapour was
produced?
1. Moles of hydrogen from ideal gas equation
2. Equation shows this equals the moles of
H 2O
3. Find mass of this many moles of gas.
e.g. 6 What will you do?
• Some glucose (C6H12O6) is burnt in a school
laboratory. Write a full balanced equation for
this
• C6H12O6(s) + 6O2(g)  6H2O(g) + 6CO2(g)
• The mass of the glucose was 14.3g. What
volume of carbon dioxide was evolved?
1. Moles of glucose from mass and Mr
2. Equation shows the moles of CO2 are 6 times
this, so multiply by 6
3. Assume normal temperature and pressure –
100kPa, 298K. (or could use 24 litres per mole)
4. Use ideal gas equation to find the volume of this
many moles of gas.
e.g. 7 What will you do?
• Some propanol (C3H7OH) is burnt in a school
laboratory. Write a full balanced equation for
this
• 2C3H7OH (l) + 9O2(g)  8H2O(g) + 6CO2(g)
• The mass of the propanol was 119g. What
mass of carbon dioxide was evolved?
1. Moles of propanol from mass and Mr
2. Equation shows the moles of CO2 are 3 times
this, so multiply by 3
3. Find the mass of this many moles of gas.
e.g. 8 What will you do?